Decorative Concrete Sealers

One of the challenges for a high quality architectural concrete installation is the selection of the right sealer. From chemical staining, discoloring, and the day-to-day abuses these surfaces receive, choosing a sealer can make or break the entire project. So, what do you need to look for in a sealer, and how do you match the right sealer to your type of project and environment?

Architectural concrete is conventional concrete that has been colored, stained, stamped, saw-cut, or sandblasted to create a creative effect or to simulate tile, stone or brick. It can also be polymer-modified -- the addition of a 1/8 to 1/2 inch decorative overlay topping — which can also be colored, stamped or stained to create the desired finish and look. Clear sealer finishes for these surfaces come in many different formulations and levels of durability, and can be applied to both architectural concrete and to polymer-modified cement overlays.

Concrete sealers provide added protection and may, if applied properly, extend the usable life of an installation. There are many sealer options made from gum resins, linseed oil, silicone derivatives (e.g., silane, siloxane, and siliconate), epoxy, acrylic, urethane, and polyurethane. Less common, and generally more expensive, hybrids like methylmethacrylate (MMA) and polyurea sealers are also options. Both water-based (typically low-solid penetratives) and solvenated (typically high-solid, high-build) coating solutions are available. Single-component and two- (or three-) component mixes are also options to be considered.

Choosing the Right Sealer
The unique characteristics of concrete and other cementitious surfaces make the selection of a sealer a serious matter. Several questions need to be asked before selecting the appropriate sealer:

• To what conditions will the concrete surface be exposed? (e.g., hot, cold, wet, night condensation, interior or exterior, ultraviolet light, etc.) Will there be heavy foot or vehicular traffic?
• What is the condition of the concrete? (i.e., new, old, moisture problems.)
• What are the schedule and budget for the project? (i.e., an accelerated application, or adequate time; sealer factored into cost of project, or required as an afterthought.)
• Are there slippage liability issues to be considered? (i.e., pedestrian traffic in potential wet conditions.)
• Are there environmental "green" building conditions that need to addressed? (e.g., local Department of Environmental Quality standards are required to be met.)

Sealer Selection Options
There are two major purposes for sealers. The first is to protect the concrete surface from moisture intrusion. The second is to help create the finish appearance desired for the application. In addition, there are other benefits to using a sealer, including lower maintenance, easier cleaning, efflorescence prevention (i.e., the appearance of white powder residue caused as residual water in the concrete evaporates leaving the dissolved salts on the concrete surface), and slippage protection.

There are two main types of concrete sealers. Those designed to penetrate the concrete, leaving it looking dry, yet water repellent, and those that form a film on the surface, giving it a wet look. Penetrating sealers are low viscosity materials that fill the surface pores of the substrate, but do not leave a polymer film above the peaks of the concrete.

Coating sealers provide better protection of the substrate and are easier to clean than penetrating sealers. However, they create a smoother surface that is more likely to present a slip hazard under wet conditions. The incorporation of aggregate particles in the coating material can help alleviate this potential liability, but requires a careful understanding of the correct size and amount of the aggregate relative to the sealer type selected for the project.

Most penetrating sealers are made from by-products of silicone called silanes, siloxanes, or siliconates, and are designed to penetrate concrete pores. Once applied, they react with the alkaline materials in the concrete mix and the moisture present to form a silicone seal, making concrete water-repellent. Penetrating sealers usually cost more, but generally last longer before repair or reapplication is required. Another reason penetrating sealers are popular is, that when properly applied, they do not change the concrete's appearance.