Self-leveling overlays can be installed very quickly. You can place and finish more product per day, per worker than with any other cast-in-place decorative product. Kirk Dalton, an owner in his family's contracting business SSI 2000 Inc., Hayward, Calif., says they've installed as much as 30,000 square feet in a single day with seven crew members. He thinks this is partly because manufacturers have improved their products, making them easier to install.
Self-leveling overlays are especially useful when substrate conditions are less than ideal: old or worn concrete surfaces, unflat or unlevel floors, and concrete surfaces that are damaged by other floor treatments. Typical applications include commercial building lobbies and corridors, retail spaces, residential floors, restaurants, and warehouse floors.
Success equals good preparation
Self-leveling overlay products are sensitive to ambient conditions. For this reason, most applications are in controlled indoor environments. Certain jobsite conditions must be managed in order to achieve good results, which include:
- Maintaining even temperature
- Controlling air movement to eliminate drafts
- Eliminating direct sunlight from reaching the work area
- Providing even relative humidity throughout the jobsite
It's very important to achieve a good bond between the subfloor and an overlay, so proper mechanical preparation of the existing slab is very important. Bead-blasting equipment and diamond grinders are the most frequently used tools but scarifiers are used as well, especially for thicker placements. Dalton says the size of a project determines the size of the equipment needed—it's all about productivity. Over time, his company has purchased both large and small bead-blasters and grinders so they can be productive on any size job. “The high voltage and amperage power requirements for these tools can be a problem also, so we now own trailer-mounted 60- and 85-kilowatt generators to provide the power we need on our jobsites,” he says.
High moisture conditions in a subfloor also can cause floor covering failures so check this before any work begins. According to Dalton, they use both calcium-chloride test kids and relative humidity (RH) probes—RH being the more accurate way to determine moisture content. “A slab with a 95% RH is too moist and you can't successfully cover it with any vapor-resistant product,” he says. “Today, it's especially important to know the moisture content of a slab because of the push toward fast track construction.”
Bruce Burton, a business development manger for Mapei, Deerfield Beach, Fla., says self-leveling overlay products are engineered blends of cement, fine aggregates, pozzolans, and admixtures that include superplasticizers, polymers, shrinkage compensators, and other ingredients. Manufacturers' mixing instructions require applicators to mix a precise amount of water with each bag of material in order to achieve the desired properties.
From the time the material is first placed on a subslab, the average working time is only about 12 minutes, followed by rapid strength development. Burton says that typical application thicknesses start at about ¼ inch but can exceed 2 inches without shrinkage or cracking problems. The hardened product is very dense and durable, has compression strengths of approximately 6000 psi, and achieves good flexural strengths.
When integral colors are added to self-leveling overlays, the final product shows strong color with no efflorescence, according to Burton.
Placing and finishing
The size of a project determines the size and type of equipment needed. A mixing drill and a 5-gallon pail might be all that's needed for a small job, while a large project can require high-volume mixers and pumps for placement. Dalton says a typical decorative project is about 1000 square feet. If product is placed with a pump, the job can be completed in an hour or less. The trick is to place new material against previously placed overlay before initial set.
The entire process of mixing and placing self-leveling overlay proceeds very quickly. Workers first apply a primer on the subslab and place the mixed material to the approximate thickness required for an area. If a floor is close to being flat, a gage-rake can be used to spread the material to the right thickness. After four or five minutes, workers wearing cleats on their shoes walk into the placed material and while standing, use a smoothing trowel on a long handle to quickly apply the final finish. Dalton says they set pins to precise elevations for projects that require very level, flat applications. “A skilled person working at the pump nozzle can place overlay material to a precise elevation without the need of a gage rake,” he says.
Sealing the finished product
Like all concrete, the finished product is susceptible to staining and attack from acid-based products, so finished work should be sealed and maintained. Burton says that any sealer for concrete that is tolerant of high pH levels is acceptable, including acrylics, epoxies, and urethane-based products. According to Dalton, stain finishes also can be applied to surfaces. His company uses a variety of spraying equipment to apply sealers, including high-volume low-pressure, airless, and pump-up sprayers.
Working in this market
Dalton's family started their business to install floor coverings, but many floors weren't flat or level. So when they realized that they were spending more time preparing floors and installing concrete underlayments than they were installing floor coverings, they refocused their business accordingly. They also discovered the advantage of using decorative overlay products to restore floors and provide a finished surface at the same time. But most of their efforts on a jobsite are spent preparing floors for overlays so they've invested in these types of tools and equipment.
Dalton knows the technology and the industry is growing and changing, and so does his competition. He keeps up with contractor friends around the country, sharing ideas and learning as much as he can about current problems and solutions. He also keeps in contact with product manufacturers he uses because they are a wealth of information.