Polyaspartic polyureas are fairly new in the marketplace and have great potential for decorative concrete because their many unique qualities differentiate them from other coatings on the market. Contractors are currently using them as clear coats over finishes such as stamped, stained, colored, and stenciled concrete and pigmented coatings, including decorative media. There is also some experimentation with applications on exterior slab-on-grade decorative work.
Aspartic esters were invented and patented by Bayer Corporation in the 1990s. Aspartic resins followed, and the manufacturer found that very dense and shiny films could form, leading to the creation of polyaspartic aliphatic polyureas. Now several companies have introduced formulations that contractors can use commercially. Their formulations share several common properties, but there are also benefits and cautions unique to each product on the market.
Polyureas are 2-component materials. The system works when a resin is mixed with a catalyst, usually a polyisocyanate, which causes a reaction and develops a polymer compound.
The benefits of a polyaspartic floor coating put traditional epoxy floors to shame. Not only are they of higher quality, longer-lasting, and way more damage resistant, but polyaspartic/polyurea floors cure in a fraction of the time it takes an epoxy floor to cure. The latest coating technology has brought many new floor coating chemicals with remarkable features compared to traditional materials:
- Depending on the product, they can be applied at temperatures as low as -30°F and as high as 140°F, depending on the product. In hot and cold climates, contractors can install them all year long.
- When cured, they can tolerate temperatures as high as 350°F.
- They are UV light stable, providing "water clear" finishes.
- Polyureas have much greater abrasion and impact resistance than epoxy or urethane coatings.
- They do not blush or whiten.
- Curing is quick, and work can be turned over to owners for use within a couple of hours after application.
- High ambient humidity does not restrict the application, although some products set more quickly in high humidity.
- Polyureas have superior wetting and penetrating characteristics, which means they form exceptional bonds to concrete. They don't stain, resist fat and oil penetration, and protect concrete from mild acids.
There are different thoughts among applicators about the preparation required for concrete applications. The type of application also matters. But it can't be argued that the excellent "wetting" ability of polyaspartic polyureas and the way they penetrate concrete makes low profile preparation for decorative concrete possible.
These "wetting" characteristics allow concrete penetration on the first application, delivering amazing bond strength.
Some contractors profile their concrete with grinders using 40 to 80 grit diamond pads. Thoroughly cleaning with a power washer may be adequate for decorative concrete receiving a thin film coating. We recommend removing the cement paste from the surface and neutralizing all soluble salts.
You know the preparation is good when the primary coat absorbs completely into the surface. Many applicators have found that applying a citric acid wash and pressure washing with a turbo tip to prepare slabs before staining. To date, we have not heard of any scaling, debonding, or other problems involving polyurea coatings.
Moisture content in concrete?
The weakest link for concrete is the sealer. Polyaspartic polyureas solve this issue. They are heat-resistant, waterproof, stain and acid resistant, and don't soften with fats or oils. Polyureas don't transmit water vapor, so they are considered waterproof. Aspartic ester polyureas "wet out" and penetrate concrete surfaces to achieve a superior bond. This bonding ability may prevent moisture vapor transmission issues. The moisture content of the concrete shouldn't exceed 3 pounds per 1000 square feet using the calcium chloride test at the time of application to ensure that the primer application will penetrate the surface properly.
The application process comprises three coatings; a primer (which penetrates the surface but is not always necessary), a "build coat" containing the decorative application if it's more than a clear coat, and a topcoat. It should consist of 20 to 25 mils in thickness when you include vinyl chips in your finish. 6 to 8 mil thicknesses are normal and provide "hiding capacity" when pigments are added.
Polyaspartic polyureas are sold as 100% solids material, with solvents added or recommendations for adding solvents. With the addition of solvents, the material is less dense, pot life is increased, and increased penetration into a slab.
Another advantage of polyaspartic polyureas is that the material doesn't outgas. Concrete still traps air, though, and it can escape into a coating after it's applied. It's best to apply coatings when ambient temps are declining. But because they set so quickly, there is less likelihood of trapping air in polyureas.
Humidity accelerates setting time. When this product is applied at 40% humidity, the setting time might be 30 to 40 minutes. But at 90% humidity, it can decrease to 15 minutes.
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