Article No: 167

2006-05-03 09:20:34
Decorative Concrete
By: Cindy Rizzo with Jan Bloom


photo sourtesy of L.M. Scofield Company

In today's hot residential real estate market, developers are running short of well-located vacant land. That's one of the reasons buildings in declining older areas of American cities are being redeveloped. Residential loft conversions in former industrial buildings are among today's most fashionable urban homes.

Clearly, the faster a renovation is completed, the sooner it can be occupied. That's one key reason architects and contractors specify self-leveling cementitious overlayments. In addition to using self-leveling overlays to resurface floors in renovated properties, these fast-drying toppings are also used to correct construction errors in new buildings. Whether it's new construction or a renovation, many contractors choose self-leveling overlays for custom floors.

Reusing old spaces in new ways
Renovating older buildings usually involves resurfacing and refinishing the floors. And in these situations, the advantages of single component cementitious toppings can really make a difference. The F.J. Cooledge and Sons Company-Hastings' Seed Company building is a perfect example of early 1900s industrial design that has been converted for new uses. The four-story brick structure was built in 1913 and used as an industrial building to house glass, paint and seed companies.

In 1940, the building was sold to the H.G. Hastings Company, publisher of the seed catalog, who used the building to ship and receive seeds and gardening materials. It also operated a retail store at this location. They sold the building in 1982 but it remained vacant until it was sold to its current owners who converted it into loft apartments and gallery space. The rehabilitation project won an Award for Excellence from the City of Atlanta Urban Design Commission in the category of adaptive use and historic renovation.

While some of the residents of this historic building kept the original tile floor, others wanted a custom floor. When a custom floor is what the client wants, polymer-modified cementitious toppings provide standout looks and performance. Designed exclusively for interiors, they offer an infinite variety of looks that are suitable for virtually every type of residence--apartments, town houses and single-family homes. These thin toppings are ideal for installation in rooms that have existing thresholds, fixtures or equipment.

Distinctive custom floors
Self-leveling cementitious overlays offer the uniqueness of a custom concrete floor but are easy and relatively quick to install--particularly when compared with the time and labor required to lay tile, marble or granite, or install terrazzo. Depending on the size of the room, overlayments can be completely installed in as few as three days, including surface preparation, material application, staining or stamping, and sealing.

Fresh, clean and monochromatic perfectly describe what's popular in American homes. Self-leveling overlays are an ideal surface on which to use decorative chemical stains to create these stylish looks. With them, contractors can produce subtle variegated color as well as more dramatic graphics. And they can stain it quickly. Typically the staining is done the next day, 24 hours after the overlay installation is completed. In fact, staining should be done within two days of installation for optimum color development.

Unlike most carpeting, cementitious toppings are non-allergenic and environmentally friendly. Some are formulated without formaldehyde or protein, don't emit noxious chemicals during or after curing, and don't create an environment friendly to bacterial growth. Not only will cementitious toppings last a long time, when they're properly sealed and maintained, they're stain resistant. In fact, they'll last for many years as long as the floor is maintained properly.

Surface preparation
As is true with just about any decorative concrete floor, nothing is more important to success than proper surface preparation. Because overlays will delaminate, crack, or the sealers will fail, don't install overlay on sub-floors made from gypsum-based materials, wood, damp concrete (or concrete with a high moisture vapor emission rate), or uncured concrete. Also be sure to remove any mastics or contaminants from the substrate surface because they'll prevent the overlay from adhering properly.

Self-leveling overlays look and perform best when they're installed over non-moving substrate that is free from surface contaminants. Because they form a thin, rigid layer on top of the sub-floor, any movement in the sub-floor will produce fine cracks in the topping. And, as with most cementitious products, cracks or joints in the sub-floor will be reflected in the topping. Make sure you place joints on top of those already in the substrate through the full depth of the topping by dry saw cutting or using forms. Wet saw cutting can stain the overlay surface.

When you're certain that there are no contaminants or coatings on the substrate surface, clean the floor and fill all the spalls with a patching material or mixture of epoxy and sand. Most self-leveling overlays require that you prime the sub-floor with a layer of epoxy and embedded silica sand before laying the topping. The primer seals the sub-floor surface and prevents the topping from losing water. It also improves the leveling performance of the cured topping surface. The embedded sand provides a high-strength mechanical bond between the primer and the overlay.

Once the sub-floor is ready, mix the epoxy primer, and pour it onto the surface spreading it evenly. Immediately distribute fine silica sand onto the wet primer so that the surface is completely covered. After the floor has been completely covered with the epoxy and sand, let it cure overnight. Then sweep any sand that isn't bonded with the primer up with a broom followed by vacuuming to remove loose particles.

Applying the topping
Always check the overlay manufacturer's technical information and follow it carefully when installing self-leveling cementitious overlays. Most toppings perform best when they're installed within a precise temperature range and if the temperature varies more than 20 degrees during the installation, it's possible that the surface will experience micro cracks. Even though these toppings are self-leveling, most require some spreading and leveling during the installation process. In most cases, you'll also need to smooth the surface to release any entrapped air. But don't over water the topping mix or overwork the surface because doing so will lead to problems in its final appearance.

Versatile and cost-effective
From single-family homes to stylish apartments in converted warehouses, cementitious overlays offer a unique and attractive alternative to traditional flooring materials. They can be installed in almost any color or design from the lightest of tints to brilliant opaque hues and their versatility enables them to mimic natural materials. By saw-cutting the topping, adding color with chemical stain, then grouting the saw cuts, a skilled contractor can emulate the appearance of ceramic tile or inlaid stone faster and at a lower price.