HOW TO GRIND CONCRETE FLOORS TO EXPOSE THE AGGREGATE

Source:www.stonediamondtool.com Date:2020/2/17 Read:296

Concrete is a common building material that is created with a mixture of aggregate, cement and water, along with other additives such as lime and acrylics or latexes to create an additional layer of elasticity to reduce cracking that could occur over time. Aggregate is used to help hold the cement into a specific form and to add consistency to the mix, plus help reduce cracking. It can be sand or pebbles or even small rocks, not all of which show through on the finish surface after it has been troweled and left to dry. To expose the aggregate, you first have to grind down the floor, after which you can polish the surface to give the concrete a mirror-like finish similar to terrazzo or polished marble.

1. Open any windows or doors to the outside if you are working in an interior setting. Remove all furniture or other things blocking the floor if you are working with an existing, lived-in area. Protect all trim and edges of the wall along the perimeter of the floor with foam padding stuck in place with masking tape. Cut down padding with a utility knife.

2. Grind down the edges of the area with an 8-inch grinder with a cup wheel or sanding disc pad attached. Place the grinder on the floor. Hold it with both hands. Pull the trigger and move the wheel/pad over the surface of the concrete to grind down the top layers.

3. Make multiple passes to expose the aggregate below, which will show up as you begin to grind down the stones to expose their interiors. Continue until you are pleased with the finish result. Keep the grinder continually moving in passes, as letting it sit in one area will grind down only in that area.

4. Grind down the overall expanse of the floor the same way as the outer perimeters. Hold the two handles of the disc sander as you stand behind the machine. Pull the triggers on the handle and hold the machine with your hands, guiding it as you walk. Keep the machine continually moving as with the grinder to avoid digging down too much in a single area.

5. Remove the dust and debris with a broom and dustpan or a shop vacuum. Replace the pads on your grinding machines with the first in your set of polishing pads and begin the polishing process, which is exactly the same as the grinding process but with smoother pads.

Tips

§ The rougher the grit, the faster you will grind down the concrete. Start with around a 30 grit and if that doesn't get the look you want, go lower. Polishing is accomplished by smoothing the initial layer down with multiple passes (at least three to five pads/passes) using incrementally finer grits of pads. Start with a 100 grit and go as high as you need for the polish you want. The more passes and the finer the pads, the greater the level of polish.

§ Not all concrete floors have a rough enough aggregate to visibly show after grinding. Aggregate can range in size from grains of sand all the way up to golf-ball sized rocks/pebbles. The finer the aggregate, the less it will show, and if you are dealing with a concrete floor that used sand during the mixture there will be no difference in material look and feel no matter how far down you grind.

§ Flatness is not the same as smooth or level. Level is inherently flat; flat is not necessarily level, and a surface can be smooth without being level or flat. If you want to actually grind down a floor until it is flat, you may need to use a concrete chipper machine, which is similar to the disc sander except that instead of pads it uses diamond-tipped cutting blades to dig into and chip/cut/eat away at the concrete as it passes over. Understand that using such a tool requires the expertise and skill of many years of use and if you need to flatten down a floor you should either expect trial and error or hire a professional contractor who will do it right the first time.

Warning

§ A dust mask is not sufficient for working with concrete grinding. Wear a respirator with a fully sealed face mask to protect your eyes and concrete-rated filters to keep the concrete/additive dust out of your lungs.