After all the creative energy, time, work and money spent producing a beautiful decorative concrete floor, too many contractors and building owners stop short of finishing the job with a coating that will protect that beauty and prolong the floor's service life. Sometimes they stop short of spending the time to select the right topcoat for the way the floor will be used. Sometimes they stop short of investing in a material that will last. Sometimes they stop short of doing the extra work or developing the skills required to install a high-performance coating.
In any case, the result of stopping short is that the artisan's work of staining, stamping, stenciling or sandblasting is compromised and largely wasted, often in an uninformed attempt to save some money in the short term.
There are many products used to finish decorative concrete. The words "sealer" and "coating" are sometimes used interchangeably, but there are differences. Sealers are typically lower-solids materials that penetrate the concrete, with minimal buildup on the top. They can protect the concrete from moisture and stains, but they do not provide a wear surface. Coatings are characterized by the visible protective film they leave on top of the concrete.
The most important consideration in choosing a coating must be the end use of the floor, including abuse, traffic, maintenance, location (interior or exterior) and desired appearance. Contractors also must consider performance, longevity, cost, application requirements and their own experience, training and preferences.
Coating materials can be classified into four general categories based on chemistry - acrylics, epoxies, polyurethanes and polyaspartic aliphatic polyureas, often simply called polyaspartics. Retailers should be prepared to offer contractors some basic information on each that will help them select the correct coating material and surface profile for a job. This article will help you distinguish between the four.
A salon floor featuring Westcoat Liquid Dazzle in EC-38 Marine.
Product description: Acrylics are one-part materials that cure by air-drying. They are available in solvent-based or water-based formulations. They are often used as sealers, as they penetrate the concrete. They leave a negligible film build on top of the floor. Acrylics are popular because they are easy to apply and have the lowest initial cost of the options available. While they do offer some protection from stains and abrasion, they are not tough enough to serve as a long-lasting wear coat.
Properties: Most (but not all) acrylics are UV stable, so they won't yellow with exposure to light. They are very clear, allowing the concrete below to show through with minimal alteration to its appearance. They are also breathable, allowing moisture to escape from the concrete below.
Limitations: Because of their low film build, most manufacturers and contractors agree that acrylics simply do not provide long-term protection. They either need to be reapplied frequently or protected by wax.
Handling: Acrylics require no mixing. Water-based formulations eliminate solvent disposal issues.
Application: Acrylics can be brushed on, rolled on, or applied with a low-pressure sprayer. Uses: Acrylics are a low-cost choice for areas where little wear is expected. They are not suitable for use where there will be traffic from cars, machinery, furniture or even heavy pedestrian use. Because of their UV stability, acrylics can be used indoors or outside.
Product description: Epoxies are two-component materials (resin and curing agent) that are sold as 100 percent solids, either solvent-cut solutions or water-based emulsions. The versatile chemistry of epoxies allows manufacturers to formulate products for a variety of specific application and performance parameters. A 100 percent solids coating can achieve a film thickness of 10 mils to 15 mils in a single coat.
Properties: Epoxies are known for resistance to stains, chemicals and wear and good adhesion to concrete and to other coating materials. Epoxies may be formulated into thin or thick topcoats, protective coatings, or epoxy polymer concrete. Adding materials such as glass, sand, stone or color chips creates a decorative composite polymer overlay from 1/8 inch to 1 inch thick. Epoxies resist mold and mildew, are allergen-free and are easy to clean. When UV exposure is not an issue, they are often the product of choice.
Limitations: Most epoxies yellow under exposure to ultraviolet light. They also show scratches, so their gloss may dull with wear.
Handling: Epoxies cure through a chemical reaction that begins in the mixing container as the two components are mixed. Pot life ranges from 10 minutes to two hours. Contractors should plan their work so as to use an entire batch before it cures. Follow manufacturers' instructions for proper mixing ratios and techniques, as products vary.
Application: Epoxies can be poured onto the floor and spread with a trowel, gauge rake or squeegee to the desired thickness, then immediately backrolled with a short nap roller to smooth out high and low spots.
Uses: Epoxies are used as clear or pigmented protective coatings and as opaque floor systems over a concrete slab. Long used in institutional and industrial settings as well as residential garages, they are increasingly popular as clear coatings in places like restaurants and beauty salons because of their chemical resistance and cleanability. Epoxies are seldom used to coat exterior applications.
Product description: Polyurethanes, often just called urethanes, are also two-component materials and are also available in 100 percent solids formulations or as emulsions carried in solvent or water. Solvent-borne urethanes deliver the best performance in terms of wear, color retenÂtion and stain resistance. They usually build a film of 3 mils to 4 mils in a single coat.
Properties: Urethanes will not yellow with exposure to light. They have a long pot life - mixed material can even be stored and used later. They cure to a hard, durable surface.
Limitations: Advances in 100 percent solids and waterborne technology have not yet caught up with the high performance of solvent-borne urethanes, with which VOCs and odor can be issues.
Application: Urethanes may be applied with standard brush, roller or airless spray equipment. Applying two coats of 3 mils to 4 mils each is preferable to trying to reach a thicker film build in a single coat. Applying two coats allows contractors to achieve a more uniform thickness and cure. It also allows solvent to evaporate more efficiently.
Uses: Urethanes can be used over any decorative concrete floor, though the solvents in solvent-borne urethanes can potentially change the look of acid stains. Because of their lower film build and slightly higher cost, they are often used in conjunction with other materials - for example, as a UV-stable topcoat over a thicker epoxy wear coating.
Product description: Polyaspartic aliphatic polyurea coatings are based on chemistry developed and patented by Bayer MaterialScience LLC. The two-component material is typically applied in three coats: a prime coat, a mid-coat that can be pigmented or flooded with color chips, and a topcoat for wear protection. Polyaspartics deliver high-performance protection at thinner coating levels Â- 5 mils to 10 mils.
Properties: Polyaspartics are known for their rapid cure times. (Three coats can be applied and the floor opened to vehicular traffic in 24 hours.) They may be applied across a broad range of temperature and weather conditions. They are UV stable and deliver excellent chemical and abrasion resistance. Polyaspartics have low VOC content and low odor. They produce an effective moisture barrier. The material is easily repairable, and damaged areas can be cut out and patched seamlessly.
Limitations: The biggest challenge in working with polyaspartics is the rapid cure time. The material must be applied within just a few minutes of mixing while it is still capable of thorough wetting. Most manufacturers require contractors to be trained and certified before they can buy polyaspartic materials. Polyaspartics telegraph imperfections in the surface below, so the concrete needs to be smooth if a contractor wants the coated finish to be smooth.
Handling: The two components of polyaspartic coatings should be mixed in small batches and applied quickly. Check manufacturer's directions for mixing - some recommend hand mixing.
Application: Concrete needs to be open and porous. Manufacturers recommend grinding the surface to a profile between 50 grit and 100 grit to achieve uniform wetting and penetration of the pores. Polyaspartics can be applied by roller, squeegee or spray.
Uses: Polyaspartics usually have the highest price tag per gallon, so they are most profitably used in situations where this cost can be offset by benefits offered by their rapid cure time or their ability to cure across a wide range of temperatures. In particular, polyaspartics can be applied in colder temperatures than other coatings. What's more, they deliver high-performance protection in harsh environments like auto dealerships, laboratories and commercial kitchens.