POLISHED CONCRETE

Concrete is fast becoming the ultimate no-wax flooring material.

Thanks to recent advances in polishing equipment and techniques, contractors are now grinding concrete floor surfaces—whether new or old—to a high-gloss finish that never needs waxes or coatings. Factor in the superior durability and performance of concrete, and it's no wonder why more retail, warehouse, and office facilities are opting for polished concrete flooring as an alternative to marble, granite, tile, linoleum, or coated concrete. Even homeowners are catching on to the appeal of these smooth, high-luster floors, which can be stained to replicate the look of polished stone.

 

 

Polishing Basics

Simply put, polishing concrete is similar to sanding wood. Heavy-duty polishing machines equipped with progressively finer grits of diamond-impregnated segments or disks (akin to sandpaper) are used to gradually grind down surfaces to the desired degree of shine and smoothness.

The process begins with the use of coarse diamond segments bonded in a metallic matrix. These segments are coarse enough to remove minor pits, blemishes, stains, or light coatings from the floor in preparation for final smoothing. Depending on the condition of the concrete, this initial rough grinding is generally a three- to four-step process.

The next steps involve fine grinding of the concrete surface using diamond abrasives embedded in a plastic or resin matrix. Crews use ever-finer grits of polishing disks (a process called “lapping”) until the floor has the desired sheen. For an extremely high-gloss finish, a final grit of 1500 or finer may be used. Experienced polishing crews know when to switch to the next-finer grit by observing the floor surface and the amount of material being removed.

During the final polishing step, some contractors spread a commercial polishing compound onto the surface to give the floor a bit more sheen. These compounds also help clean any residue remaining on the surface from the polishing process and leave a dirt-resistant finish.

Standards for Polished Concrete

There are not published standards for polished concrete, but it is generally agreed that the concrete must be polished through the sequence of disks ending with 1800-3500 grit diamonds to be considered polished concrete. At this level the concrete will exhibit a glossy sheen and high reflectivity without the use of a topical coating.

Polished concrete in not simply exposing the rock in the concrete mix then applying a sealer.

Benefits of Polished Concrete

During the polishing process an internal impregnating sealer is applied. The sealer sinks into the concrete and is invisible to the naked eye. It not only protects the concrete from the inside out, it also hardens and densifies the concrete. This eliminates the need for a topical coating, which reduces maintenance significantly (versus if you had a coating on it).

When the concrete is brought to a full polish- there is no need to apply a topical coating or wax. Waxing the surface would be defeating the purpose of a fully polished floor- because the concrete floor itself is already shining, so there is no need to put something on the floor that would then need to be maintained.

Options with Polished Concrete

If the decision is made to polish concrete in advance of the concrete being poured, there is a stunning array of available options:

· Colored aggregate can be applied to the concrete mix or “seeded” into the top layer of the mix. The polishing process will reveal these aggregate.

· Integrally colored concrete can be used.

· Glass can be “seeded” into the mix. The polishing process will reveal the glass pieces.

· Nails, bolts, computer chips, or any other objects can be seeded into the mix and then polished smooth.

· Of course, any of these options can be combined together or into a pattern.

Not Polished, but Still Awesome

As noted earlier, polishing concrete required a series of polishing steps culminating with the use of 1800-3500 grit diamonds. Each step in the process increases the shine and reflectivity of the concrete.

There are other options, which though they stop short of 1800-3500 grit diamonds, are still beautiful:

Two steps of grinding to expose the aggregate, then applying a topical sealer, might be called the “exposed aggregate, sealed look.” While still taking on a polished look, the polish is a result of a topical coating (still beautiful, but requiring more maintenance).

A “honed finish” stops at 220 grit diamonds. This “honed finish” has some surface shine, but is still smooth and easy to clean.

It is usually a good idea for the customer to review the floor at the 400-800-and 1800 grit diamond level of shine if the customer is unsure if they want a fully polished look (though most clients do want the floor fully polished). Clearly, there are many levels of floors that stop short of truly being “polished concrete”, but are beautiful in their own right.

Wet vs. Dry Polishing

Contractors can polish concrete using wet or dry methods, but typically they use a combination of both. The wet process uses water to cool the diamond abrasives and eliminate grinding dust. Because the water reduces friction and acts as a lubricant, it increases the life of the polishing abrasives, particularly the resin-bonded disks, which can melt at high temperatures. A disadvantage of the wet process is the mess. Crews must collect and dispose of the slurry that's generated, which slows productivity.

Dry polishing requires no water. Instead, contractors use machines equipped with dust-containment systems that eliminate virtually all of the mess. Typically dry polishing is used for the initial grinding steps, when more concrete is being removed. As the surface becomes smoother, and crews switch from the metal-bonded to the finer resin-bonded diamond abrasives, they generally change to wet polishing. However, some manufacturers have introduced resin-bonded disks that are designed to withstand the friction of dry polishing, allowing the entire process to be done dry. This is rapidly becoming the method of choice for most contractors.

Can All Concrete Be Polished?

Almost any structurally sound concrete floor, whether new or old, can be polished. But there are some exceptions. For new floors, no special mix design is required to achieve good results. However, the floor should be in place at least 28 days before polishing begins to ensure adequate curing. Some retail and warehouse facilities that plan to polish their floors after placement may specify the installation of as smooth a floor as possible to minimize the polishing steps required.

Existing floors typically require some surface preparation prior to polishing to remove dirt, grease, coatings, or blemishes. However, floors that are wavy, need extensive patching, or are extremely porous may not be good candidates for polishing. An experienced contractor can usually determine a floor's suitability.

To help solidify and densify polished concrete surfaces, some contractors apply penetrating hardeners to the concrete, normally after the first step of the grinding process. These products, which can be applied to new or existing floors, work by reacting chemically with the concrete to form a hard, crystalline structure. They also prevent dusting of concrete and offer extra protection from water penetration and staining.

Applications for Polished Concrete

Because polishing is a multistep process, customers can choose the level of sheen—from satin to high-gloss—that meets their maintenance and aesthetic requirements. This versatility makes polished concrete an ideal flooring material for a variety of applications. Polishing contractors say their primary customers include:

· Large warehouses and warehouse outlets

· Retail stores

· Hotels and restaurants

· Office buildings

· Auto showrooms

· Private residences

Ease of maintenance is the key reason many warehouses and retail facilities are opting for polished concrete. Not only are polished floors easy to clean, requiring only occasional damp mopping, they hold up well to heavy forklift and foot traffic. They also eliminate the need for messy waxes or coatings—as well as the associated labor, time, and expense to apply them. What's more, the glossy surface resists the marks of forklift truck tires and staining from oil and chemical spills.

The high light reflectivity of polished concrete is another important benefit, especially for office buildings, hotels, restaurants, and other public facilities that want to project a bright, clean, professional image. Some customers simply want a look that's unique. Polishing can give concrete a higher degree of shine—similar to polished marble or granite—than can be achieved with a high-gloss coating. This makes polished concrete a particularly good alternative for homeowners or businesses that can't afford marble or granite floors but want the same brilliant, mirror-like finish. To replicate the color of stone, it is possible to apply stain to the concrete during the polishing process or polish concrete that has been integrally colored. It's also possible to produce a terrazzo look by grinding through the top few millimeters of the concrete surface to expose the aggregate.

Copyright © 2005 SurfaceTechs