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May 1, 2009
The most in-demand type of construction product is one that is both environmentally responsible and less expensive than non-green alternatives. By that standard, polished concrete flooring is a product whose time has come. One of the greenest flooring options available anywhere, it boasts other benefits that range from economic to aesthetic.
Demand for polished concrete is rising, driving further advancements in the technology, leading to better results, containment of costs and increasing options.
One recent advance pioneered by a Vancouver-area contractor also makes the polishing process significantly greener. David Loe, a polishing industry veteran of 10 years, recognized the need for a densifier/hardener that was easier to apply and didn’t have the caustic waste disposal problem of existing materials.
Loe began experimenting with colloidal silica, which eliminates caustic waste, is faster and easier than previous products, and actually brings down densifying labor costs. After using it himself for four years, he formed Lythic Solutions (www.lythic.com) and made the material available under the trade-name Lythic Densifier.
One prime reason that polished concrete is both affordable and sustainable is that, in many buildings, concrete is already there as the subfloor. In remodels, the concrete is essentially free: it was paid for when the structure was built. In new construction, it’s built into the budget; the cost usually referred to as “flooring” is the cost of floor-covering over the concrete.
The cost of uncovering and polishing concrete competes with the least expensive floor coverings, yet it can rival some of the most expensive in terms of appearance.
Being “already there” also makes it more sustainable: no additional floor covering materials are consumed. Moreover, concrete does not emit volatile organic compounds, nor does it require installation-adhesives or maintenance with solvents that emit VOCs as many other flooring options do.
The U.S. Green Building Council’s LEED 2009 certification system specifically mentions polished concrete, and it can contribute to LEED points including EQ Credit 3.2 (Construction IAQ Management Plan Before Occupancy), EQ Credit 4.3 (Flooring Systems), and other possible credits based on its reflectivity of light, which reduces energy consumption.
According to Michael Chusid, an architect working as a consultant to Lythic Solutions, ID Credit 11.5 (Innovation in Design) may be made possible by using colloidal silica densifier.
“It eliminates the caustic residue disposal and reduces job-site waste,” Chusid said. “Also, it ships as a concentrate, so it reduces transportation-related energy consumption. All these factors may be considered for credit.”
Sustainable is beautiful
Do the math (or the science) and it’s easy to see why many people are choosing concrete as their floor. A less obvious motivator is polished concrete’s beauty. Environmental and price advantages don’t require a trade-off in appearance. Polished concrete offers a wide variety of looks that can rival the attractions of terrazzo or polished stone, or achieve uniquely concrete appearances.
There are several methods of coloring concrete, and artisans are pushing the envelope, using colors for intricate, creative patterning. If the concrete is being newly made with polishing in mind, it can be designed for special looks for truly one-of-a-kind floors.
The polishing explosion
The 1990s emergence of polished concrete was powered by several technical advances, including improved diamond grinding hardware, optimized chemical densifiers, and advanced techniques for coloring and patterning. These human and technological resources are now broadly available.
The process that evolved, excluding the variables of decorative techniques, is simple and straightforward:
1. Diamond grind for smoothness and evenness
2. Densify for hardness and better impermeability
3. Diamond polish for appearance
Grinding and polishing steps are done with the same large machines tooled with diamond abrasives; the difference is the fineness of the abrasives. Modern machinery grinds and removes dust with high efficiency.
The middle step, densification, is a chemical application that makes the surface harder and less permeable to liquids. Densifiers react with lime in the concrete to fill tiny pores with new cement-like material, making it harder, denser and able to take a better polish.
Closing the pore-structure contributes to polished concrete’s sustainability. The densified surface is more abuse-resistant, extending its useful life, and resists liquid penetration well, making it easier to clean. Simple water-based cleansers are sufficient, avoiding harsh chemicals and solvents, and the VOCs they emit. It minimizes places for microbes or allergens to collect (a big advantage over carpeting), improving indoor air quality. Being inorganic, concrete does not support the growth of mold.
“Densifying makes concrete more sustainable,” observes Lythic Solutions President Loe. “The only environmental issue was with the process, and I think we’ve solved that now. This colloidal silica product is 10 to 100 times less alkaline than the first generation densifiers. Colloidal silica doesn’t need scrub-off, and therefore produces no caustic slurry to dispose of. This completes the sustainable credentials of polished concrete.”
Brad Sleeper, a polishing professional with Sustainable Flooring Solutions in Vancouver, has used many types of densifiers, and believes colloidal silica is an improvement from both environmental and business standpoints.
“The older sodium silicate densifiers have to be scrubbed off scrupulously,” explains Sleeper. “It’s messy and labor-intensive, and anything left behind forms a hard deposit we call ‘whiting’ that can only be removed by regrinding the slab. Colloidal silica makes the job much faster, cleaner and less costly.”
Grinding affords some of the aesthetic choices. Light grinding only cuts into the top layer, providing a finely grained surface with minimal color variation. Deeper grinding to expose aggregate sand and gravel that make up much of the slab’s interior can yield terrazzo-type effects.
A new slab can be made with different colors of aggregate to blend or contrast with the concrete’s color. “Creative” aggregate can be included: colored recycled glass chips, screws, seashells and other durable objects. When ground off, they become eye-catching cross sections that make a unique and expressive floor.
Color is the other main creative control. Integral pigments produce the most consistent color. Stains and dyes can create relatively even coloration, or pronounced mottling. Colors can be combined, patterned or layered.
After densifying and possible coloring polishing with finer abrasives begins. Different levels of polish afford further appearance options, from a light sheen to a deep gloss. Mirror-like reflections are possible.
Reflections in a unique floor
After polishing, the floor is done. It does not need to be sealed or waxed under most conditions. It is likely to stay glossy for many years under normal wear. And, since every slab is a little different, a simple concrete floor can be utterly unique.
Sustainable, cost-effective, practical and aesthetically versatile, polished concrete is a flooring solution that can save a lot of dollars and make a great deal of sense for both new buildings and remodels. Polishing the slab turns a basic component into an added amenity, at the same time as reducing the burden on the planet.
A creative aggregate concrete gallery
If the slab is being newly placed with polishing in mind, specialized aggregate can be used in the mix to create unique effects. Selecting the coarse aggregate rock for its color can create contrasts and harmonies when using ordinary gray cement or with integral color added to the mix. Other objects added to the mix can take on an unexpected and intriguing appearance when they are ground off during the polishing process.
Photos by Steven H. Miller
Steven H. Miller, CDT, CSI, is an award-winning freelance journalist and photographer focusing on construction issues. He is a consultant to Chusid Associates, a technical and marketing firm specializing in construction products.