As polished concrete increases in popularity, many people are discovering that it is harder to keep up than they thought. The concrete floor was once common only in garages, but over the last decade, industrial buildings in large cities have been turned into lofts and condominiums. Their concrete floors are polished to a marble-like luster that is garnering much attention from design magazines and home improvement enthusiasts.
Today, polished concrete slab is being used not only as flooring, but also as a cheap alternative to stone counter tops. If you want the polished look, however, and want to avoid the high cost of hiring a professional polisher, you will need to learn how to polish concrete yourself. Other places where you may need to polish concrete are patios, lanais, driveways, walkways and pool decks.
Is Your Concrete Ready to Polish?
Almost all concrete slab can be polished. If you are laying your own concrete floor or countertop however, it is important that it is completely dry before you start the polishing process. In most cases wet concrete will have to sit for three days before it is dry enough to polish. To test it for dryness, use a power sander on a small, out-of-the-way segment. If the sander kicks up large pieces of sand, wait another twenty-four hours before trying again.
Some concrete slab has been painted, lacquered or otherwise finished. It is important that your concrete be completely free from finishes or inlays before you start polishing. Although the polishing process will remove the finish as you go, it can be difficult to see how deep you are going if you are not starting out with a clean slate. Any inlays in your concrete slab can result in an uneven finish with rough, unpolished patches.
Once your concrete floor is dry and all finishes have been removed, it must be thoroughly cleaned, patched and sealed. You should use an industrial strength solution made out of butyl cleaner and degreaser to clean the floor. Make sure that the cleaner has dried completely before you start patching any holes, chips or cracks.
As far as patching goes, the best material for the job is a concrete adhesive patch. Using a chisel, you can cut out and shape any existing holes so that they are larger on the bottom than on the top of the concrete slab. Mix the adhesive according to the instructions on the package, and apply the patching compound to each hole, using a trowel to smooth it out even with the surface of the floor.
If you are refinishing a floor, use a layer of self leveling concrete instead of individual patching. Self levelling concrete quickly allows you to refinish a concrete floor that has become uneven or pitted from traffic, weather, or subfloor movements.
After patching, it is recommended to apply concrete sealer. This will protect the bare concrete against wear and corosion. There are several types of concrete sealer, but the two most popular are acylic and epoxy.
Acylic concrete sealer forms a thin film resin membrane on top of the bare concrete, and results in a finish that will enhance the look of your concrete and protect it against UV sun damage. Not only will it block surface moisture from above, it will also protect against moisture from below, since it penetrates the cement pores. It tends to make floors slippery when wet, so you may want to consider add an anti-skid compound to the finish. ALthough not as long lasting as epoxy concrete sealer, it is less expensive and easier to apply, making it the best choice in most cases. Acrylic is also available as a wet look sealer which is good for stained concrete projects.
Epoxy concrete sealer is very strong and durable. In fact it is so tough that it can trap moisture beneath itès surface, resulting in eventual cracking and bubbling in the finish. This makes is somewhat more difficult to apply than acylic sealant. But if your primary consideration is durability rather than appearance, epoxy sealants are a better choice. A concrete shower, for example, may be better to finish with epoxy selaer.
Other types of concrete finishers include silanes, silicates and siliconates. These are sometimes applied to the bare concrete substrate as a primer for the topical epoxy or acrylic finishes.
How to Polish Concrete to Shine like Marble
Those wondering how to polish concrete without an orbital sander polishing machine are probably not going to want to hear this, but unless you are prepared for weeks of intensive manual labor, the only viable option is to use a power sander. Fortunately, concrete polishing kits are becoming increasingly common. Plus a number of hardware and flooring stores have started to rent out orbital sanders to consumers.
An orbital sander is a sanding machine where the motor turns a rotating disk, as opposed to a belt or drum sanding machine. A more recent improvement in orbital sanders is the random orbit sander. The random orbit sander features dual rotation, of the both the sanding disk and the driving head. As a result, random orbit sanders have the high sanding spped of a belt sander, combined with the ability to produce a fine, polished finish of a traditional orbit sander.
When polishing a concrete floor, you will want to start out with 50-grit diamond disks on the machine. As you grind the floor, the disks will slowly wear down, so it is important to check on their condition frequently and to replace them as needed.
Wet the floor before you start with enough water to keep the surface of the concrete wet. Slowly push the grinder from behind, walking in straight lines back and forth across the room. When you are done, the floor will be covered in a paste made from water and ground concrete powder. Rinse the floor and inspect it carefully. Redo any sections that you missed, then rinse the floor again.
You will now need to repeat the entire process, replacing the 50-grit disks with 100-grit disks. Make sure to keep your steps even and deliberate, to avoid creating unnecessary swirls or unevenness in the floor. Once you are done with the 100-grit disks, you can further smooth out any imperfections by first using 200-grit disks, then upgrading to 400-grit disks.
Although a standard grinder can easily polish the main part of the concrete floor, it often has trouble reaching into corners and getting to the ends of edges. To finish the entire floor, you will need to use a right-angle grinder. Starting with 50-grit, then upgrading to 100 grit sandpaper, 200-grit and, finally, 400-grit disks, run the right-angle grinder around the edges of the room, paying special attention to any rough areas that the standard grinder could not reach. Even though the process can be tedious and time-consuming, you will be left with a beautiful, lustrous floor, the knowledge that you know how to polish concrete, and the satisfaction of a job well done.
Photo of polished concrete patio by supremecrete, Creative Commons Attribution