Polished concrete has become a popular flooring option due to its modern, attractive design aesthetic and durable, low maintenance finish. It requires no waxing or special sealers, and is simple to clean. Like anything in the construction industry, special care must be paid in order to utilize this finish in an effective manner. When considering polished concrete, several things should be discussed with the project team before construction begins.
1. A level surface is key.
The levelness of a pour is key to a uniformly polished floor. To maintain a consistent aggregate exposure and sheen, the slab shouldn’t vary more than one-sixteenth of an inch across the surface. Flatness is measured in levels (referred to as the FF rating). An FF rating of 50 is advised, since the finish-grinder is relying on a flat surface to achieve a uniform grind that will expose the aggregates (salt & pepper sprinkled effect). If the areas are not precisely leveled, differences will be evident in the appearance of the aggregate.
2. Big spaces are easier to level.
Buildings with smaller rooms (e.g., residential spaces) require pours to be broken up by room and must be leveled by hand. In larger spaces (e.g., breweries or stadiums) the pour will be smoother since a laser screed can be used to help level the floor. In this case, the cost of the laser screed technology will need to be built into the budget. If the space is too small to utilize a laser screed, research can be done to find a local concrete contractor that can deliver FF 50 ratings via hand finishing. While an option, hand finishing isn’t always recommended. To ensure maximum finish consistency, employing laser screed technology is suggested.
3. Protection should be high-priority.
During construction, slab protection becomes critical to preserve the integrity of the concrete until finishing can begin. Since the concrete slab is typically poured at the beginning of a project, the slab is exposed throughout the duration of construction. From the moment the concrete is poured until the moment it gets polished, it must be protected from damage. Depending on the desired class of aggregate exposure, some topical damage (spilled paint, for example) may not be ground away. To protect the slab, plywood mats below man-lifts, temperature control measures, and plastic boards with sealed joints can all be used. Since the concrete will cure and evaporate moisture once it has been poured, ‘breathable tape’ (not duct tape) is recommended for joints. Using tape that doesn’t breathe could result in trapped moisture that would leave lines on the slab after temporary protection is removed. Moisture lines could catch finishing stain and sealer and potentially ruin the slab.
4. Cracking can be expected.
Due to the nature of the product, concrete slabs can crack as the building settles into place; but with proper care, cracking can be controlled. Adding fibers to concrete pre-pour can help reinforce the material, and strategically placing control joints to isolate slabs can account for the shifting of the building’s steel support columns. Additionally, while the industry standard for concrete depth is four inches, it can be increased in order to gain stability.
In the right setting, a polished concrete finish can offer long-term durability and sophisticated beauty. By taking special notice of space, protection and attention to detail, even the most intricate polished concrete project can go a little smoother.
This blog post was a collaboration between Gibson Luck and Ryan Byrd, both of which were involved in polished concrete application during the Hope Church project.
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