Concrete

Concrete Stain:

Stain manufacturers differ on when to apply stain. Some say that a new slab must cure for 28 days before work is started. Others suggest 14 days. Installers sometimes prefer to do their work as soon as possible after the concrete is placed.

When choosing how to apply stain, keep the following things in mind:

  • Colors are more intense if stain is applied soon after concrete is placed. Stain diluted with water and applied immediately can often achieve the same results as full-strength stains applied later.
  • Water drives the chemical-stain reaction. To achieve color consistency, make sure the moisture content of the concrete is roughly the same for every placement colored. If one concrete placement is stained 2 days after its placed, then other placements should be stained when they are 2 days old for color consistency.
  • Staining, sealing, and covering finished work before other construction trades return to the area saves on cleanup, achieves a better-looking installation, and makes damage repair during the rest of construction easier to handle.
  • More Concrete Staining Issues

There are many ways to apply stain, with each method providing a different final appearance.

Sprayers often are used to apply stains, but they should be rated for acid and have no metal parts. Acid will quickly destroy metal parts, which can affect the color of the stain. Miller advises using a spray tip with a circular pattern, spraying in a pattern that goes from left to right and then right to left, with someone scrubbing the stain into the surface using a medium-bristle brush in a circular motion just behind the spray. It's important to scrub in the stain and not just push it around. An additional spray pass just behind the scrubbing removes brush marks. This method ensures good penetration and minimal marking from either the sprayer or brush.

The increased interest in chemical-stain finishes is in the direction of more subtle effects. Installers frequently dilute stains with water to produce less intense effects. For example, one contractor often applies the stain the day after the concrete is placed, starting with a 3% stain dilution (3 parts commercial stain to 97 parts water by volume), and then adding more acid to increase the strength to 10%. In this manner, the contractor can gradually build up color to meet owner expectations. Second and third colors can also be added in the same fashion to create color overlays. Sometimes a stained overlay is the best solution for concrete surfaces that show damage or have been abused during construction. Commercially available overlay materials can be integrally colored, textured, and stained to provide a new range of decorative possibilities. The overlays have high flexural strength and wear resistance. As with everything involving stains, however, it's wise to create a sample to ensure compatibility of the overlay cement with the stain and to get owner approval for the result.

Concrete Epoxy:

There's a good reason why concrete is used almost exclusively for floors in basements and garages, warehouse facilities and manufacturing and food processing plants -- it's one of the few materials durable enough to stand up to the heavy traffic, abrasion, chemicals, and moisture exposure these surfaces are often subject to. However, that doesn't mean concrete slabs are indestructible. Left untreated without a concrete coating the porous materials that concrete is made of can succumb to extreme abuse, such as tire traffic, exposure to harsh chemicals and deicing salts, and frequent moisture contact.

That's where a good protective coating comes into play, giving concrete that extra layer of protection it needs to endure constant wear and tear. In addition to its protective function, a coating can also dress up a drab surface, simplify maintenance and improve skid resistance.

Concrete Sealing: 

You've finally installed the concrete masterpiece of your dreams. Maybe it's a pattern-stamped pool deck or patio, an interlocking paver driveway, an acid-stained floor, or an exposed-aggregate walkway.

Protecting and properly maintaining that concrete will keep it looking spectacular for many years to come while extending its service life. And even if the surface begins to show wear after years of exposure to traffic and the environment, you can often restore its original beauty with special cleaning, stain removal, and polishing products.

Broom Finish Concrete:

Concrete finishers have been broom finishing their surfaces for about as long as there has been concrete. Typically decorative concrete surfaces are not broom finished, although dyes and stains can be applied very successfully to broomed finishes. Even stamped finishes can be broomed, although that's a bit difficult—impossible if you are using a powdered release agent. There are better ways to make stamped surfaces slip resistant, which we will get into later.
The typical process for a broom finish is:

  • Pour the slab
  • Strike off with a screed
  • Bull float
  • Wait for the bleed water to evaporate—although with low water-cement ratio exterior concrete with the proper amount of air, there might not be much bleed water. Bleed water is a result of the wet concrete settling and with entrained air, it doesn't settle much and therefore little water comes to the surface. The proper amount of air is always critical in any exterior concrete that will be exposed to free-thaw action. For concrete with ¾ or 1-inch aggregate, order the concrete with 6% entrained air (plus or minus 1%)—and make sure you are getting it, otherwise the surface will spall. For smaller aggregate you need more air—7% for ½ inch and 7.5% for 3/8 inch.
  • Trowel—there's some disagreement here. In many cases, today's finishers won't trowel a slab that's getting a broom-finished surface, just bull float and broom. One veteran finisher, however, told me "I like to use a fresno to get the bull float lines out." Bob Simonelli, with Structural Services Inc., says that some troweling is OK, "but be careful not to over-finish the surface and work some of the air out." Advice in a 1996 edition of Concrete Construction's Problem Clinic, however, says you can trowel twice before brooming, but be sure to keep the trowel flat during the second troweling and begin brooming "immediately after the second troweling." If you get the surface troweled hard, it will be difficult to get much texture. PCA's Cement Mason's Guide says to use a damp broom after troweling.
  • Broom the surface by running a concrete broom perpendicular to the slope, if there is one. On concrete that's intended to drain, though, broom marks should be run towards the drain. One thing to note is that a broom-finished exterior surface is just as durable as a smooth finish.
  • Cure the concrete—You can (and must) cure broom-finished concrete with sheets of polyethylene or by spraying on curing compound. For plain gray concrete, a curing agent with some color (typically white) in it helps you to see where it's been applied. The color dissipates after a few weeks. For decorative concrete, use a cure & seal. Don't forget the curing!

A good broom finish is something of an art. You can even create decorative effects by running the broom texture in various directions. Typically the broom should be run from side to side of the concrete without stopping. With a standard broom, you should pull the broom towards you, then lift it and set it back on the far side to pull it across again. Marion Brush makes a brush (the Auto Glide) where the head automatically tilts to the correct angle, so you can get a good broom finish whether you are pushing or pulling the broom.

Hard Trowel Finish Concrete:

Troweling produces a hard, smooth, dense surface and should be done immediately after floating.Troweling can be done by machine or by hand .If done by hand, the finisher will float and trowel and area before moving his knee-boards.

Salt Rock Finish Concrete:

As the name implies, a salt finish is traditionally achieved with the same coarse rock salt sold for use in water softeners or as a deicer in winter. Concrete finishers broadcast the salt particles over wet concrete and then press the grains into the surface with a float or roller. After the concrete sets (typically after 24 hours), they power wash the salt away, revealing a speckled pattern of shallow indentations left by the dislodged salt particles.

Natural rock salt finish:

While salt imprinting is relatively quick and easy to master, there are newer methods that can speed up the process by doing away with the salt altogether (see "Ways to Produce a Salt Finish, Without the Salt").

Salt finishes are more commonplace in the warmer western and southern regions of the country. The reason: In areas subject to freezing weather, water tends to collect in the indentations and freeze, potentially causing spalling. But if you like the look and use good-quality concrete protected by a waterproofing sealer, a salt finish should be durable enough to endure any climate.

Concrete Overlay:

A stamped overlay offers all the aesthetic benefits of conventional stamped concrete but is less time- and labor-intensive to install. The overlay mix is usually applied by a gauge rake (a tool with an adjustable depth gauge for achieving a uniform topping thickness) and then imprinted with stamping mats or texturing skins. These semi-flexible stamping tools are available in dozens of patterns, allowing overlay installers to duplicate the beauty and texture of natural stone, brick, slate, wood planking, and other materials. Overlay thicknesses range from 1/4 to 3/4 inch, depending on the depth of the imprint.

Microtoppings & Skim Coats:

These ultra-thin decorative toppings are applied by a trowel or squeegee in layers as thin as 20 mils, or a mere 0.02 inch. They can go on silky smooth and taken down to a featheredge. Or you can apply several coats to create a textured broomed or troweled finish. Some systems come pretinted in a wide range of colors while others can be custom tinted by mixing in the desired amount of liquid coloring agent. Interesting color variations can be achieved by applying layers of different hues.

Spray-down systems:

These versatile systems offer a wide array of finish options. Usually they are sprayed evenly onto concrete with an air-powered hopper gun, but they can also be applied as a splatter coat to create a textured, slip-resistant surface or "knocked down" with a trowel to create a smoother finish. A popular decorative technique is to use paper or adhesive stencils to produce designs ranging from decorative borders and medallions to tile patterns to embossed or inlaid motifs.
Self-leveling overlays

These flowable polymer-modified toppings have the ability to self level without troweling, making them ideal for smoothing and leveling worn or uneven concrete surfaces. Installers simply pour or pump the material onto the surface and then use a spreader to distribute it evenly. The overlay can be left seamless (except at control joints) or used as a canvas for sawcut or engraved designs. Or you can incorporate decorative inlays, such as strips of wood or metal, by adhering them to the base concrete and then pouring the overlay to the level of the inlay. Self-leveling overlays can also be enhanced by staining or dying. In some applications, they serve a purely utilitarian purpose as an underlayment for tile, carpet, or other floor coverings.

Epoxy Terrazzo Toppings:

This mosaic-like floor topping is known as thin-set epoxy terrazzo, a poured-in-place topping for concrete substrates that goes on at a thickness of only ¼ to 3/8 inch. It is excellent for multi-colored patterns and designs because of the epoxy resin matrix. It can be pigmented, like paint, to achieve an unlimited spectrum of colors. It can also be colored with aggregates, including chips of marble or granite, recycled glass, mother of pearl, and various synthetic materials. Read more about epoxy terrazzo toppings.

Cleaning Concrete:

A wide variety of cleaners are available that are designed to clean or remove contamination from concrete surfaces. Understanding what these different cleaners do and how they work can save you time and money on your next cleaning project.

First, without going into complex chemistry, let's discuss how a basic soap works. We all know that oil and water do not mix. Soap consists of fatty acids that emulsify oil, grease, and dirt, allowing the particles to be removed with a water-based solution. Without soap, just plain water doesn't have much cleaning ability. By surrounding and entrapping stubborn oil or organic-based dirt, a soap or cleaner allows the grime to be rinsed away more easily.

The origin of basic soap goes back hundreds of years, and today there are a multitude of modern detergents and cleaners to choose from. Some utilize complex chemistry to target specific types of contamination and dirt in a wide variety of environmental conditions.

Even with the best cleaner, good old-fashioned elbow grease and patience really make the difference when removing a stubborn stain from concrete. Concrete is porous, holds dirt well, and can be a tough surface to clean. Doing some research and trying a few different systems can really pay off. Once you find the cleaner that really works, you will cut your time for concrete surface preparation or maintenance in half.

Acid Staining:

One of the most popular ways to achieve color is through acid-staining. Chemical stains can be applied to new or old, plain or colored concrete surfaces. Although they are often called acid stains, acid isn't the ingredient that colors the concrete. Metallic salts in an acidic, water-based solution react with hydrated lime (calcium hydroxide) in hardened concrete to yield insoluble, colored compounds that become a permanent part of the concrete.Several companies manufacture chemical stains that are variations of three basic color groups: black, brown, and blue-green.

"Designers are waking up to the fact that there's more than wood, carpet, and tiles. There's nothing that can't be done."
-Richard Smith, Richard Smith Custom Concrete

The acid in chemical stains opens the top surface of the concrete, allowing metallic salts to reach the free lime deposits. Water from the stain solution then fuels the reaction, usually for about a month after the stain has been applied. Other factors that affect the outcome include:

  • Cement properties and amount
  • Admixtures used
  • Type of aggregate used
  • Concrete finishing methods
  • Concrete age and moisture content when stain is applied
  • Weather conditions when stain is applied
  • Efflorescence

Decorative Concrete:

New developments in decorative concrete are offering architects, designers, builders, homeowners and contractors more choices to creatively customize each project for any style, building type or decor. First, we are seeing improved installation efficiencies that reduce costs adopted in response to economic realities today. Second, more products are going green since that has become the most significant influence on buying decisions. Third, a greater diversity of creative choices are stimulating interest and demand. This year, there are better products with innovative installation methods for use in different areas of the home. Let’s take a look at the top trends that are redefining decorative concrete.

TOP TREND # 1: Expanding the range of green and gorgeous colors.

The palette of decorative concrete color choices just exploded. Dramatic light reflective metallic effects are the latest trend. Dyes are available to achieve intense color accents. New environmentally-sound, water-based concrete stains are gaining converts by making it possible to choose from a range of vivid colors or pastels. The water-based stains also reduce installation time and costs by eliminating the messy neutralizing and residue removal steps required with acid stains. Whether used alone or alongside the earth tones that have long been popular, these new concrete coloring options are appealing for artisans and property owners alike.

According to concrete artisan Shellie Rigsby, “Stunning finishes for concrete are changing the scope of creative options for interior design. Metals can produce an edgy high-tech modern look or may be used to produce an aged patina. For rustic or traditional decor, there are many excellent choices for ceilings, walls or other architectural details. The new avant-garde color trends are ideal for special effect finishes such as iridescent, true metals, shimmers, reflective elements and other effects made possible by new products.”

TOP TREND # 2: Concrete countertops have escaped the kitchen.

With improved materials choices, the same process used for forming concrete countertops is now being applied to furniture and fixtures in areas beyond the kitchen – indoors and out. Concrete countertop mixes can be used to achieve unique, custom shapes for benches, occasional tables, desks, fireplace surrounds, bars and entertainment areas. The latest trend is to use GFRC, glass fiber-reinforced concrete, in the mix to provide strength, so no extra reinforcing is necessary.

A variety of shapes can now be custom-made and there are almost limitless design possibilities using stains, dyes, pigments, colored aggregates and other materials made popular in decorative concrete.

TOP TREND #3: Concrete patterns are replacing carpeting for accent areas.

Concrete floors can even be produced in glorious patterns that rival area rugs for artistic beauty. The decorative arts and decorative concrete are converging as artisans elevate stenciling to a skilled craft. Easy-to-use Modello stencils set the industry standard. The company offers a stencil library of thousands of sophisticated patterns that can be ordered custom-sized and cut to order for either grand or petite projects.

“Modellos,” the brainchild of Melanie Royals, provide a reliable means of transferring custom designs onto floors, walls or ceilings using adhesive-backed patterns popular with decorative painting and decorative concrete contractors. Why are homeowners choosing concrete instead of rugs? In areas where indoor air quality and hygiene are of paramount importance, concrete floors offer the environmentally sound solution and provide superior durability. Concrete “carpets” stay where they are put down, and won’t harbor dust mites and other allergens like carpets, can’t mold or mildew, and won’t out-gas like polyvinyl and some composite materials.

TOP TREND #4: Concrete polishing just got easier.

The environmental benefits of concrete polishing are now attainable for residential use due to recent innovations in products and equipment. Although light-colored, light-reflective monochromatic polished floors are often selected to reduce energy demand, many color choices are available for polished concrete. Low-VOC, environmentally-friendly coloring products can be used during the process to add elegant colors that harmonize with other building materials.

Architects are often surprised by the variety of appearances that can be achieved by specifying exactly the level of reflectivity to be produced during polishing. Different sizes and colors of aggregates or recycled glass chips can be selected for use in the concrete mix, and then exposed when the top surface is removed during grinding. The amazing results rival granite and terrazzo in appearance and durability, but win on price. Grinding and polishing concrete first became popular for retail and commercial settings subjected to food or petro-chemical spillage. The hard and dust-free concrete surface that is produced when a densifier is used dramatically have reduced maintenance costs and liability claims from slip-fall hazards in big box stores.

Since then, new equipment has made installation more efficient. The process has been widely adopted for schools and child-care facilities because it ends the use of harsh chemicals for cleaning and eliminates the cost of additional floor coverings on top of the existing concrete slab. For all these reasons concrete polishing has been accepted as an innovation in materials use that improves indoor air quality to meet LEED criteria for green building, as set by the United States Green Building Council.

TOP TREND #5: The new direction is vertical.

Vertical decorative concrete offers the newest opportunity for skilled artisans to provide homeowners something wholly personal. There are many creative techniques for artistic walls and features to suit any home. The craft of artificial rock forming is one that is reaching a new level.

Stamp Concrete:

If imitation is the sincerest form of flattery, then stamped concrete, sometimes referred to as patterned concrete, flatters like nothing else can, with its amazing ability to closely replicate, in both color and texture, popular paving materials such as cobblestone, brick, fieldstone and slate, to name a few. Yet stamped concrete surpasses these traditional favorites in many ways, offering greater versatility, economy, long-term performance and ease of installation. Here's an introduction to the proliferation of possibilities with stamped concrete and some pointers on ensuring a high-quality installation that will last for decades.

Stamped concrete may have built a reputation as a consummate copycat, but today it's gaining respect for its design flair. Unlike masonry pavers or natural stone, cement offers myriad options for customization because it can be shaped, imprinted, textured and colored to achieve almost any look imaginable. With concrete, stone that looks like the natural material can be economically recreated when patterns are pressed into the concrete. Stamping concrete can also blend harmoniously with just about any landscape or architectural scheme, making it suitable for all types of exterior hardscaping—and some interior applications as well.

The best news is that because stamped concrete is a customized product, it can be tailored to suit your individual design goals and budget, whether you want to achieve a natural look or be wildly innovative.

Pea Gravel Finish Concrete:

Step 1 - Planning

Don’t underestimate the amount of time and effort required to do a good job of finishing concrete in exposed aggregate. I think it takes a DIYer about double the amount of time it would take to apply a conventional finish, not including acid washing, and clear-coating. Don’t attempt to do too much in one day, or without an adequate number of workers. I have found that using two helpers (total 3 workers), with everyone working pretty hard all day, we could do about 125 square feet on a hot day at the very most. On a cool cloudy day, we could manage about 50 square feet more. On a very hot day, the concrete sets nearly as fast as we could mix and pour it, and it was taxing to manage 80 – 100 square feet per day. Using less than two helpers drastically reduces the amount of surface that can be poured and finished in a day. Make sure your equipment and material is at the job site before you begin. Make sure all forms are fully set, and that you are not going to be distracted by last-minute details like cutting and installing rebar or remesh. Have any ramps and planking necessary for maneuvering wheelbarrows in place beforehand. Clear the workspace of any unnecessary obstacles and hazards. If you are using water from a well, consider whether the well has the capacity to supply the large amounts of water you will need for mixing and washing the finished surface (also consider the upshot of underestimating this). Also consider that you will need water for cleaning tools, and after a hard day’s work, you’re going to want a shower. If your project requires you to pour in sections, consider which sections are going to be poured first, and arrange to protect the already finished surface(s) against spills and other workplace damage. Consider where the wash-water is going to go, and try to avoid washing across an already finished surface.

Step 2 - Prepare the aggregate material.

The pea gravel used will have a strong influence on the final appearence of the project. Spend some time selecting the pea gravel that best suits your sense of asthetics. Selection can be based on any combination of shape, colour, texture (smooth, fractured, shiny, dull), and to a lesser extent, size. Some landscape supply outlets may have a range of choices, and may be able to order material to meet your specification. If you are attempting to match an existing exposed aggregate slab, this step will be particularly importent. Thoroughly wash the pea-gravel, about 6-8 gallons at a time in a wheelbarrow, until the water is clear when mixed around with the gravel. Keep the cleaned gravel nearby, and fill the plastic pails with the gravel. This is best done the day before.

Step 3 - Pour the base.

Pour the concrete into the forms, tamping, spreading, etc. as for an ordinary poured surface. If the concrete is being mixed on site in batches, leave about 1" of the forms unfilled. When the forms are completely filled to within 1" of the top, finish filling the forms to within about 1/4" from the top. Use the 2-by-4 screed to level the top surface, and then smooth with the wooden float and the steel trowel.  You want to have a top surface that is flat, and is rich with concrete 'cream'. Work the concrete only enough to bring up a good layer of cream, and avoid excessive working. You will have to use some judgment as to how flat the surface is, as the screed cannot ride on the top edge of the forms as is normally done. The reason for leaving the top surface below the top of the forms is to allow room for the final layer of pea-gravel. The top layer is best poured in as few batches as possible, so that there is a consistent degree of wetness to the entire top surface. This aids in the following steps. Allow the concrete to sit until there is no more water on the surface. You want the surface to be stiff enough to support a bit of weight, like a pail of rocks on your 2-by-2 foot piece of plywood, but soft enough to press the pea-gravel into without too much effort. As the water rises to the surface, you want to take notice of any low areas that tend to accumulate water, and trowel these out so the surface is as flat as possible.

Step 4 - Seed the aggregate surface.

When the concrete has just started to set, it's time to seed the aggregate into the top surface. Fill a pail with the clean pea gravel, and using a gentle sweeping motion, cast a layer of pea gravel onto the wet concrete. The gravel should not sink under it's own weight, but remain on the surface. Use a brush to distribute the gravel evenly, so that the concrete underneath is almost entirely concealed. For a large surface, you may need to set up some type of scaffolding to gain access to the areas away from the perimeter. Try to achieve a very uniform spreading of the gravel, and avoid leaving any areas with too much concrete exposed. Any area of exposed concrete larger than a nickel is too big. Also avoid regions of excess gravel, as there will not be enough concrete cream to bond the pea gravel to the substrate, and this will result in a hollow area with unexposed pea gravel. At this stage, you may notice some areas that do not have enough cream at the surface to bed the pea gravel in. Mix a batch of sand and cement, about 3:1 or 4:1, fairly wet, and apply it over the pea gravel as needed to completely surround any loose gravel.

Step 5 - Press the stones into the concrete.

This step can begin as soon as an area is uniformly covered with the pea gravel. Start by pressing the gravel into the surface with a wood float, or just a block of wood, such as a 12"-18" piece of 2-by-4. Use a pressing or gentle tapping motion. At this stage you may start to see areas that require a few additional stones, so drop a few stones in place as necessary, and start pressing them in. By now, the concrete should be becoming fairly stiff, so that you can lean on it with your hand without leaving an impression. You will probably need to apply some small patches of the mortar mixture in various places as you start placing and pressing the gravel. Make sure there are no lumps of mortar sticking up above the overall surface. Use the brushes to gently spread the mortar over a wide area. Brushes of the right stiffness can be used in a tapping motion, where the ends of the bristles tap the stones into the concrete. This has been found to be an effective way of bringing up a bit of moisture and cream, as well as working any applied mortar around loose stones. When you have pressed the gravel into a large area and are satisfied that there are no voids or piles of excess gravel, begin rolling the gravel into the concrete with a lawn roller. If the weather is hot, you will have to start working fast at this stage. Roll the gravel until it is completely pressed into the concrete, and the roller begins to draw up a thin layer of concrete fines around the pea gravel. Don't worry about the gravel disappearing into the concrete. It should be pressed in so that the top surface looks uniformly covered with the concrete fines. At this stage you should be able to tread gently on the surface to push the roller. Avoid any twisting motions with your feet, and try not to dig in your heels or toes, which may leave impressions in the surface. As you roll the surface, try to avoid steering the roller while it is actually on the concrete, as the twisting motion will tend to lift stones out and leave pits. If the concrete is too soft at this stage you may see ridges forming along the edge of the roller. If this happens, stop rolling and wait a few minutes, until the concrete has stiffened enough to fully support the roller. If the gravel becomes difficult to roll into the concrete, you can give the concrete a very light mist of water to loosen it up slightly. Don't overdo this, as it will substantially reduce the strength of the concrete and reduce the bonding strength of the cement to the stones. All of your workers should be very busy at this stage, pressing, rolling, and always scanning for imperfections. Eventually, the stones will all be pressed into the concrete, and the entire top surface will be covered with a thin layer of cream. No bare stones should be exposed.

Sometimes, if the concrete becomes too dry, it will tend to cause the stones to stick to the roller. If this happens, make sure the stones are removed from the surface of the roller before the roller makes a full revolution, or the ‘extra’ stone will cause an indentation in the surface. A very fine mist of water applied to the surface will generally cure this problem. Now that the stones are all pressed into place, get down low to the surface, and sight across it, looking for any ridges left by the roller. If you see any, and you probably will, either roll them out, or get a 2 foot block of 2-by-4 and lay it flat across the high spot. Give it a few whacks with the mason's hammer, up and down the board. Move the board around and repeat until the high spot is flattened. Keep scanning across the surface and get it as flat as possible.
Take a short break. If it is a cool day, this might be as long as an hour. If it is a hot day, it might be only 5 or 10 minutes.

Step 6 - Expose the aggregate.

When the concrete fines on the surface have lost the shiny wet appearance, and have become a dull colour, it is time to start exposing the aggregate. Begin by gently brushing the surface with a soft bristled brush or broom. Gather the fine concrete into small piles, as you begin to reveal the shapes of the stones in the concrete. If any stones get lifted out by brushing, stop and wait a little longer. As you brush, remove just enough material so that the shape of each stone becomes clearly defined, but not so much that the stones are standing up above the surrounding concrete. You aren't trying to remove all of the concrete, just enough to be able to see the shape of the individual stones. The colour is going to remain the colour of wet concrete. To gain access to the interior surface, use the piece of plywood to kneel on. Be sure to keep your toes from digging into the soft concrete, and dislodging any of the stones or leaving impressions in the surface. Brush the piles of sand and cement off of the surface. At this point the concrete should be becoming pretty hard; hard enough to walk on, and the brushing may start to require some effort to reveal the shapes of the stones. Eventually, you will have removed all of the excess material, and the surface texture will have a pebbled appearance (big surprise!), but will still be the color of wet concrete. Next is the moment of transformation. Gently spray the surface with a garden hose sprayer. Wash at a low angle across the surface to reveal the stones, and gently brush with a soft broom to move the remaining bits of sand and cement from the surface. The transformation from the dull grey of the wet concrete to the brilliant wet clean stones is a remarkable sight. Your hard work is being rewarded before your very eyes. As you brush off the last remnants, look for any areas that are not sufficiently exposed. Used a brush to finish these areas and wash it some more. Avoid using a strong spray, as this will dislodge the stones, and leave small pits in the surface. By now, you should be able to walk freely on the surface, but continue to use caution not to kick any stones out of the substrate. If any do get accidentally removed, they cannot be put back in at this point. You will notice the effect of the roller on the stones, at this stage. The stones will have aligned themselves so that a flat section of each stone is at the surface, and the top plane of the finished surface is quite smooth. My patio is quite comfortable to walk on with bare feet.

When the aggregate is fully exposed, it will still have a slightly hazy coating of cement on it. This will weather off over time, but may be etched off using muriatic acid. The aggregate will have a dull grayish coating on it, which will seem to disappear when it is wet. It is a good idea to keep the surface damp for a few days, if possible, after it is poured. This will allow the slab to reach its maximum strength. A variety of clear-coat finishes are available at home centres, plastics suppliers, and some paint stores. These should be applied according to the manufacturer’s directions, which usually stipulates that the surface should be kept dry for some period before and after application. Most will tend to leave a glazed appearance, similar to the effect of water on the exposed aggregate, which most people find pleasing.

Colored Concrete:

For many admirers of decorative concrete, the best attribute is that each installation is totally unique. Concrete can assume nearly any shape, design, pattern or texture. But the one characteristic that most distinguishes decorative concrete is color, whether used subtly to blend with nature or boldly to make a dramatic design statement.

Frankly, unless you're a purist and prefer concrete in its plain-gray state, there's no reason not to enhance it with color. The number of different products for coloring concrete has never been greater, and many manufacturers offer an extensive palette of shades to choose from for colored concrete . And although you'll pay more for colored concrete, the amazing transformation will be well worth the investment. In the hands of a creative contractor, these coloring mediums permit an endless array of decorative effects, from rustic earth-toned sidewalks and patios that harmonize with the surrounding landscape to vibrant multicolored floors that double as works of art.

Ready Mix Concrete:

With all the equipment, tools, and materials you need to purchase for your decorative concrete work, it's easy to neglect the obvious - the concrete itself. Yet ordering concrete should never be an afterthought. Because the material serves as the foundation for all your artistry, its quality and suitability for the job are paramount. By not making this purchase a top priority, you are inviting disaster and risk botching the entire project.

Your first step is to find a reputable ready mix supplier (through sources such as Find a Product) who can supply the material you need at the right time and at a fair price. But that's only the beginning. Placing the actual order is where things get complicated, since concrete is not an off-the-shelf product you can simply shop for out of a catalog.

Aggregates Finish Concrete:

Exposed aggregate finishes are perfect for patios, driveways, walkways, in bands or fields, and many other flatwork applications.
The rock (aggregate) in the concrete mix is exposed by either water pressure, chemical application, or by sandblasting.

The aggregate can be purchased from a material yard for "seeding" in the fresh concrete mix. Or the ready mix supplier may have colorful aggregates suitable for seeding or poured integral in the mix and then exposed by sandblasting.

Ask the ready mix supplier to view the aggregate they have suitable for exposing.

There are a variety of "looks" achieved by exposing the aggregate:

Available aggregates vary widely from region to region, so the look can be different merely by the region of the project.
The amount of aggregate exposure can vary from light to heavy.

Sandblasting aggregates can produce a heavy or fine aggregate exposure. In addition, some fields that are side by side, or in a pattern, can be sandblasted to different exposure levels for an interesting effect.

Timing is critical in exposing aggregate both in how soon the concrete can be "seeded," and in the timing of exposing the aggregates if the water or chemical method is being used.

Cleaning exposed aggregate concrete soon (after 2 weeks) is important to remove any cement paste residue and brighten the exposed aggregates. See cleaning exposed aggregate concrete surfaces.

Sealing exposed aggregate concrete with a clear coating, consisting of acrylic resins, brings out the natural color of the aggregates. See sealing exposed aggregate concrete surfaces.

Properly placed exposed aggregate concrete, in either bands or fields, contrasts beautifully with colored, scored, sawcut, stamped, or textured finishes.

Cured Concrete:  

When most people think of curing, they think only of maintaining moisture on the surface of the concrete. But curing is more than that—it is giving the concrete what it needs to gain strength properly. Concrete strength depends on the growth of crystals within the matrix of the concrete. These crystals grow from a reaction between Portland cement and water—a reaction known as hydration. If there isn't enough water, the crystals can't grow and the concrete doesn't develop the strength it should. If there is enough water, the crystals grow out like tiny rock-hard fingers wrapping around the sand and gravel in the mix and intertwining with one another. Almost sounds like a horror movie—our concrete baby has turned into a monster!

The other important aspect of curing is temperature—the concrete can't be too cold or too hot. As fresh concrete gets cooler, the hydration reaction slows down. The temperature of the concrete is what's important here, not necessarily the air temperature. Below about 50 F, hydration slows down a lot; below about 40 F, it virtually stops. Hot concrete has the opposite problem: the reaction goes too fast, and since the reaction is exothermic (produces heat), it can quickly cause temperature differentials within the concrete that can lead to cracking. And cement that reacts too quickly doesn't have time for the crystals to grow properly so it doesn't develop as much strength as it should.

So in the soon-to-be famous movie, the Cement Monster That Enveloped the World, all the puny earthlings need to do to save civilization is get the concrete too cold, too hot, or too dry and he turns into a weakling. Our objective, though, is to help him envelope the earth and to make him as strong as possible!

Re-Barring:

Smaller Reinforcing Is Better in Thin Slabs

The size of reinforcing steel in a concrete countertop is an important consideration because countertops made with rebar too large in scale for the slab thickness are susceptible to telegraph cracking.

When concrete shrinks due to drying, high tensile stresses develop around proportionally oversized reinforcing. These stresses cause cracks that run along the length of the steel. Smaller-diameter reinforcing has less of an effect on the concrete, so the same amount of concrete shrinkage develops much lower tensile forces, thus dramatically reducing the likelihood of cracks caused by the steel. Because all concrete shrinks to some degree, and shrinkage occurs over a long period of time, the occurrence of telegraph cracking may not appear until long after a countertop is installed.

In addition, oversized reinforcing occupies so much space inside a thin countertop slab that very little cover is left between the steel and the slab surface. Generally, reinforcing is fabricated in a grid arrangement, with strands running along the length of the slab and overlapped strands running across the width of the slab. When stacked, larger rebar can take up half of the total slab thickness, while smaller rebar occupies much less space.

In addition to causing large stress concentrations in the concrete (and therefore increasing the likelihood of telegraph cracking), using oversized reinforcing actually decreases the load capacity of the concrete. In the drawings, the same concrete is reinforced with equal amounts of steel reinforcing (based on cross-sectional area). The top drawing shows one piece of 3/8-inch-diameter (#3) reinforcing steel while the bottom drawing shows four pieces of 3/16-inch structural reinforcing wire. The cross-sectional areas are the same, so the tensile capacity of the steel is the same. But because the four pieces of wire can be located lower in the slab, the load capacity of the wire-reinforced concrete is now 13% (lower reinforcing layer) to 78% (upper reinforcing layer) greater than the slab with the single #3 rebar, even though the same amount of steel is used in the concrete. In actuality, the structural wire has a higher strength than the rebar, so the difference in capacity is even greater.

Rebar that is too big also places a significant amount of the steel closer to the visible surface of the countertop instead of down near the bottom of the slab. For example, a grid made from 3/8-inch-diameter rebar held only 1/4 inch away from the bottom (the bare minimum cover for such a size) places the top of the rebar at the midpoint of the slab, leaving only 1/2 inch of concrete cover between the steel and the visible surface. A grid made from 3/16-inch-diameter wire held 1/4 inch away from the bottom of the slab leaves 7/8 inch of concrete between the surface and the steel, a 75% increase in cover. More cover means less likelihood of telegraph cracking.

Concrete Frame Conversions:

So, how does soil bearing capacity relate to the size of footings? The footing transmits the load into the soil. The lower the bearing capacity of the soil, the wider the footing needs to be. If the soil is very strong, the footing isn't even strictly necessary just the soil under the wall would be enough to hold the building up.

Minimum Width of Concrete or Masonry Footings (inches)

Load-Bearing Value of Soil (psf)

1,500

2,000

2,500

3,000

3,500

4,000


Conventional Wood Frame Construction

1-story

16

12

10

8

7

6

2-story

19

15

12

10

8

7

3-story

22

17

14

11

10

9


4-Inch Brick Veneer Over Wood Frame or 8-Inch Hollow Concrete Masonry

1-story

19

15

12

10

8

7

2-story

25

19

15

13

11

10

3-story

31

23

19

16

13

12


8-Inch Solid or Fully Grouted Masonry

1-story

22

17

13

11

10

9

2-story

31

23

19

16

13

12

3-story

40

30

24

20

17

15

Source: Table 403.1; CABO One- and Two- Family Dwelling Code; 1995.

You can look up the recommended footing size, based on the size and type of house and the bearing capacity of the soil. As you can see, heavy houses on weak soil need footings 2 feet wide or more. But the lightest buildings on the strongest soil require footings as narrow as 7 or 8 inches. Under an 8-inch-thick wall, that's the same as saying you have no footing.

These numbers come from assumptions about the weights of building materials and the live and dead loads on roofs and floors. The allowable bearing capacity of the soil under the footing has to equal the load imposed by the structure. Reading down the table, you see that the code calls for a 12-inch-wide footing under a two-story wood-frame house in 2,500-psf-bearing soil. A 12-inch footing is 1 square foot of area per lineal foot, so the code is saying that the portion of a two-story wood house that bears on the outside walls weighs about 2,500 pounds maybe a little conservative, but reasonable. The same size footing is called for under a one-story house if it has brick veneer the brick is assumed to weigh as much as a whole second story.

If you had an engineer design the footing based on soil testing numbers and your prints, he'd add up the actual weights of the concrete, wood, and brick you'd be using in your building, factor in the required live loads, and come up with an estimate of the weight your actual house puts on the footing. It might be a little less or a little more than the code assumes. Then he would take the known bearing strength of the soil what a square foot of the soil can be trusted to support and design the footing so that the area under the footing multiplied by the bearing strength of the soil would equal or exceed the actual load.

In any case, I wouldn't recommend that builders cut back on their standard footing size even if they know they're building on strong soil. Regardless of bearing requirements, masons and poured-wall contractors want footings for their block or their forms to sit on. But the lesson to take is that when soils are very strong, (4,000-psf capacity or better), the footings may not be strictly necessary from the standpoint of bearing. This means it is less important, for example, whether the wall is correctly placed in the center of the footing.

Antiquing Release:

With stone or brick stencil patterns, the use of a texture roller or seamless texture skins will give the surface a more realistic, slightly roughened profile. With tile patterns, there is no need to texture the slab, Instead, a trowel can be used to smooth over any imperfections.

Before texturing, a liquid or powdered antiquing release agent is applied to the surface. When the slab is firm enough to accept the roller's weight and still plastic enough to receive the texture, workers can begin to go over the slab with the roller. Where the roller creates depressions in the surface, the pigment leaves shadows that mimic natural color variations. Manufacturers offer rollers with different textures to allow contractors to produce a variety of decorative effects.

A powdered antiquing release is cast onto the surface.

A texture roller is passed over the slab.

As soon as the slab has been textured, it's time to remove the stencils. This is when the "wow!" factor comes into play and the pattern is revealed. The last piece of stencil laid is removed first, with a person standing on either side of the slab and lifting the stencil straight up from the ends. After the stencil is completely clear of the surface, it's carried off to the side and disposed of.

Lifting the stencil from the slab surface.

Texturing Skins:

Texturing skins are simply much thinner versions of stamps. They are used to impart texture (such as the roughness of a natural rock face) to the wall surface rather than the deeper, well-defined patterns made by stamps. They can be used alone or to pretexture the wall surface before stamping or carving. In addition to the more commonplace brick and stone patterns, vertical stamps and skins with unique designs and textures are available from the following sources:

  • FossilCrete: Options include bamboo, brick, country cobblestone, cut coral, log cabin, weathered wood, split-face granite, and The Great Wall of China, a stamp set molded directly from the actual centuries-old wall.
  • The Stamp Store: Choose from animal tracks, boulders, fossils, leaves, sealife and tree bark patterns.
  • Tajma Wall: Offers a vertical stamp set that replicates the look of old timbers, complete with knotholes, graining and natural splits in the wood.
  • Rock and Water: A source for texturing skins cast from real rock surfaces and fossils.

Stamping Mats:

Stamped concrete is more popular today than ever before, even though the technique originated on the West Coast way back in the 1950s. Why is decorative stamping now all the rage? One of the main reasons is the availability of better concrete stamp mats and concrete texturing tools that produce very realistic results. Many people can't tell the difference between stamped concrete and pricier paving materials such as natural stone, slate, or brick.

If you were to flip through the pages of a decorative concrete history book, you'd probably come across old photos of the first concrete stamps. These stamps were made from cast aluminum and resembled giant cookie cutters with handles attached. Although these early tools were great for imprinting basic brick or stone patterns in fresh concrete, they didn't impart any texture so the results looked unrealistic in comparison with what you can achieve today. Now, most concrete stamps, or stamp mats, are made of durable polyurethane and molded from the real materials they mimic, resulting in stunningly authentic textural effects.

Concrete stamps are manufactured in hundreds of different patterns that mimic the aesthetic qualities of natural stone and other materials. Stamp patterns include brick, slate, flagstone, cobblestone, fieldstone, fan stone and many more. Patterns are commonly made to resemble stone yet these rubber stamps can also be made to resemble wood, rock salt finishes, broom finishes, fossils, or leaves

Concrete Surface Preparation: 

Preparing concrete surfaces for coatings, overlays, stains or repair materials is a time-consuming task that many contractors perform begrudgingly or are tempted to overlook altogether. But if you've ever skipped this essential first step in the process, you undoubtedly learned the hard way how critical it is to the success of the job.
"Lack of surface preparation causes 90% or more of overlay failures," says technical expert Chris Sullivan. The surface needs sufficient 'bite' for the overlay to bond, otherwise delaminating failure can result." Sullivan contends that for most decorative overlay projects, contractors should devote more time to surface prep than to the actual overlay installation itself.

Fortunately, an arsenal of high-performance equipment is available that can help you make the most efficient use of this time, enabling you to achieve the exact surface profile you need with less effort and mess than ever before possible. The most effective weapons for getting your concrete floors into shape are shotblasters, concrete grinders and scarifiers. Within these equipment categories, you'll find a wide array of models with applications as diverse as the products themselves, from compact handheld units for small jobs or working in tight spots to high-productivity ride-on machines for covering large expanses quickly. Many of these machines also come with an assortment of attachments, allowing you to remove a variety of different coatings and perform profiling tasks ranging from light roughening to aggressive milling. And in many cases, there's no need to worry about dust and debris. Machines that use dry-cutting methods usually have dust-collection capabilities, minimizing the cleanup work necessary before you apply a decorative treatment to the surface.

Concrete Repair:

For some concrete repairs, the best repair material is simply high quality concrete. But manufacturers have developed some excellent repair materials that include various polymers leading to higher bond strength and durability. Most repair materials today are polymer-modified concrete, meaning that the basic material is a portland cement and aggregate mixture with a polymer (typically latex) added. A couple of important factors in selecting a repair material are:

  • Prior to deciding what repair material to use, make sure you know what the intent is: Are you trying to bond a crack together or just cover it up?
  • Does the mortar need to stick to overhead or vertical surfaces? Or can it be very flowable to pour into forms or cracks?
  • How quickly do you want the repair to achieve full strength?
  • Do you want to use a one-part material or are you willing to use a two-component material that may be more difficult to work with but have superior properties?
  • One of the most important characteristics of a good repair material is very low shrinkage. The concrete matrix has already gone through its shrinkage, so if the repair material shrinks, it will debond and the repair will fail.
  • How important is bond strength? Usually very important--most repairs will be considered failures if the repair material doesn't bond to the concrete matrix. A big part of getting good bond is surface preparation.
  • Consider the dimensional characteristics of the repair material: Drying shrinkage can debond a repair. If the repaired area will be under load, the elastic modulus should be similar. Thermal coefficients (the rate at which the material expands or contracts with temperature) should also usually be similar.
  • Does the repair material need to be freeze-thaw resistant?
  • Does the repair material need to allow water vapor transmission? Water vapor pressure from within the matrix of the concrete can create very high pressures—easily strong enough to debond many repair materials.
  • How important is compressive strength or flexural strength? How about abrasion resistance?

Most repair materials are polymer based. Prime Resins

Accent Staining Concrete:

Customers can pick or create designs to add to new concrete or older installation. Just send a picture.
Guidelines:

  • Accent Staining has no size or detail restrictions. A recent order was as large as 17 ft x 12 ft.
  • Accent Staining can be weeded negative (etch the design into the concrete), positive (etch everything except the design) or no weeding. "No Weeding" allows the applicator versatility on the job site to weed out the design as the job progresses.

First...Prepare the Surface

Here are three basic products that open the slab for Accent Staining, and decorative overlayments. The products are most applicable to prepare a slab for sprayable or thin over-lays.

  • Gelled Acid: It bites into existing concrete surfaces removing laitance—the smooth cream on top that prevents other products from bonding. It lifts mastics and glues, opens steel troweled slabs burned almost "black and blue". A gelled Acid creates the profile that readies a slab for overlay material. Use a ventilator suitable for acid vapor and have good ventilation.
  • Tek Gel for Profiling:, the workhorse product is a medium grade prep material—a little less aggressive with the concrete. It is an excellent product to prepare a slab for thin overlay applications. Neutralizer is not necessary because the gelled acid products neutralize with water. Use a fan for ventilation if you are indoors.
  • Tek Gel for Stenciling: is the least aggressive product by design. It is the chief product used for Accent Staining. It offers precision micro etch for designs, logos and lettering without removing all of the top laitance. This benefit allows applicators to use acid based stains as accent coloring after the design is etched and opens the surface enough to allow water based stains to penetrate and bond.

The Accent Staining process is straight forward and the tools required are simple.

  • Complete necessary surface preparation using appropriate products to clean the surface. Make sure the slab is free of loose particles and dry.
  • Have the Stencil ready along with your tools—paintbrush, protective plastic, masking tape, rags, buckets and water for cleanup.
  • Affix adhesive backed Stencil to the concrete.
  • Etch the design into the clean surface using Tek Gel for Stenciling. For secondary accent coloring, do not remove the Stencil. Use a soft paintbrush and lightly brush exposed areas to increase removal of laitance and any acid stain. Clean etching material from the slab. Use a bucket and a rag to sponge off exposed areas. Use caution–do not disturb the bond of Stencil to concrete.
  • Get ready to color.

Concrete Polishing:

Polished concrete is fast becoming the ultimate no-wax flooring material. Thanks to recent advances in polishing equipment and techniques, contractors are now grinding concrete floor surfaces, whether new or old to a high-gloss finish that never needs waxes or coatings.

Factor in the superior durability and performance of concrete, and it's no wonder why more retail, warehouse, and office facilities are opting for polished concrete flooring as an alternative to marble, granite, tile, linoleum, or coated concrete. Even homeowners are catching on to the appeal of these smooth, high-luster floors, which can be stained to replicate the look of polished stone.

Concrete Calculator: http://www.concretenetwork.com/concrete/howmuch/calculator.htm


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