Texturing techniques
There are several techniques for texturing concrete. One is stenciling, which will be addressed in a future column. Another is exposing the aggregate to create a natural-looking, visually interesting surface that is also slip-resistant and hides marks and spills. This texturing technique is even more attractive when the concrete is integrally colored to complement the aggregate.
A simple, natural-looking alternative to sandblasting to expose aggregate is to remove the top layer of cement paste by hosing or scrubbing. Applying a top surface retarder makes this process more predictable and results in a higher quality finish. The viscous liquid retarder is sprayed, brushed or rolled onto freshly placed concrete and slows the set of the surface without affecting the setting rate or strength gain of the underlying concrete. This surface can then be hosed off during the next 8-20 hours, revealing the underlying aggregate. In contrast to sandblasting, a top surface retarder exposes the aggregate without abrading or scarring it. A unique look can be achieved by hand-seeding aggregate to harmonize with colored concrete and other landscape elements. A top surface retarder also allows the contractor to vary the surface, exposing the aggregate only in selected areas.
Contractors and designers have even more options when they use imprinted or "stamped" concrete. Using embossing skins or imprinting tools to texture concrete adds significant value to the project in the customer's eyes. A gray concrete driveway is just a driveway, but an imprinted driveway with a decorative look upgrades the appearance of the whole house.
A successful imprinted project begins with the pour. A contractor should order a "stamp" mix from the ready mixed supplier with coarse aggregate of 1/2 to 3/4 inch and a slump of 4 inches to reduce bleed. Care should be taken to ensure framework is square if the imprinting pattern to be used is square. Also, the tops of the stakes should be even with or lower than the top of the framework for consistent tool placement. Most importantly, be sure not to pour more concrete at a time than can be imprinted before it sets. For a contractor new to imprinting, a pour of 4 to 5 yards is a good size. Experts familiar with the tools can often imprint up to 20 yards. Best results will be achieved by being patient and taking adequate time.
Adding color
Color is an important element for enhancing the effect of imprinted concrete. A simple, efficient way of using color is to introduce an integral color admixture to the mix. Integral color admixtures deliver consistent color throughout the slab while adding strength and hardness to the concrete.
Another popular way of coloring concrete for texturing is applying dry shake color hardeners. These materials offer a wide color range, including bright, opaque colors. They also enhance the strength and hardness of the concrete surface.
Release agents also can add color to the project. These are required to allow the imprinting tool to be lifted without pulling up the cement paste. There are two types - powder antique releases and clear liquid releases. Liquid releases are cleaner than powder and the finished effect is visible as soon as the texturing tool is lifted. However, they do not add color by themselves. Powder or "antiquing" release agents are the most popular for adding single or multiple additional colors to a project. The fine powder settles in the deeper parts of the imprint, so what remains after the surface is washed is a color that complements the integral or dry-shake color of the concrete and adds a natural, dimensional look. One caution: applying a powder release too liberally will prevent a crisp, sharp imprint.
Finally, color can be added using a chemically reactive stain. Typically available in earth tones, a stain used over an embossed surface makes the imprint come alive and take on the appearance of natural stone. Stains also can be applied by hand to small sections of an imprint to add an accent.
Texturing tools
Of course the most important element in an imprinted design is the texturing tool itself. The simplest tools to use are embossing skins. Embossing skins have no "grout joints," only face texture. They are thin, flexible mats that are placed randomly in any direction for an overall look of natural stone such as slate or limestone. They give the illusion of large sections of stone. Control joints can be placed wherever they are required without diminishing the appearance.
Rigid, interlocking imprinting tools are available to create regular running patterns such as brick or tile, or more random looking patterns such as pebbles or fractured stone. Rigid or "platform" tools have not only face texture but they also have grout joint impressions. Interlocking tools fit together like a jigsaw puzzle. In a set, all of the tools have the same outside dimension but the grout joint placement might be different. These tools must be locked together in a predetermined fashion for the pattern to look realistic. Select tools that fit tightly together to prevent "squeeze" lines formed by gaps.
Tools should be set in place, not dropped or slid. The imprint is created by applying weight, either by standing on the tool, also known as walking it in, or using a tamper. The pressure should be applied evenly to get a realistic impression from the tool and to avoid birdbaths or blowouts.
Curing, sealing
To make sure the finished project looks its best for a long time, colored, textured concrete should be properly cured and sealed. Using a concrete curing compound engineered to be compatible with the color compounds is the most reliable way to ensure proper cure. Adding water or simply air curing can leach soluble salts from the concrete and cause efflorescence or lighten the color. Plastic coverings should never be used to speed the cure of colored concrete as they can leave marks or cause discoloration.
Imprinted concrete will stay nice longer if it is sealed. Sealers protect it from damage caused by weather, water stains, petroleum products, deicing salts and abrasion. They also make cleaning and maintenance quicker and easier. Sealers adhere best to a clean surface, which allows a good bond to develop with the concrete surface after full cure has been achieved. Pressure washing risks damaging the fresh imprint and removing the antiquing release by blowing off the top surface. A better method for cleaning is a water hose with low pressure and a soft broom. It is slower, but very controlled.
This is a basic overview of texturing concrete. A contractor new to these techniques has a wonderful opportunity to add value and increase profits, but he or she should remember three things.
First, be patient. Take the time to learn and practice with each new coloring or texturing method. Practice with imprinting tools on a sand base to get the right tool placement and layout and to get a feel for the tools before using them on concrete. Build enough time into a project to avoid rushing.
Second, do not promise more to customers than you can deliver. Better to do a few patterns well and gradually build skill and reputation than to experiment on each job than run the risk of committing costly errors.
Finally, take full advantage of training offered by tool manufacturers. This gives you and your crews practice and experience in a risk-free environment and teaches far more details than can be included in an article like this one.
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