How to Polish Concrete Countertops

• Polishing concrete countertops is not dangerous, but water and electricity do not mix well. If your polisher doesn’t have a Ground Fault Circuit Interrupter, be extremely careful to avoid electrocution. Even with a GFCI, it’s a good idea to wear rubber gloves to help insulate yourself.
• Wear a particle mask if you’re doing any kind of dry grinding, concrete dust is caustic.

Step 2 – Cast Finish, Light Polish, Ground Finish

• From a single piece of concrete, a range of finishes are available depending on if you polish, and how deep you polish.
• Uniform Finish – The concrete has a uniform color, because when it’s being cast, there is a thin layer of cement paste that forms on the inside surfaces of the form work.
• Light Polish – As soon as you begin polishing the surface, the thin layer of cement is removed, and the fine sand aggregate is exposed.
• Ground Finish – As you polish deeper into the concrete, you begin to expose the larger aggregate in the concrete mix.

Step 3 – Grinding vs Polishing

• Grinding can be thought of as the roughest way to flatten a concrete surface. Polishing is when you take that ground surface to a progressively smoother, shiny finish.
• When doing pre-cast concrete projects, it’s not usually necessary to use a grinder. Since the formwork is doing most of the shaping, the only place you would need to use a grinder would be on a part of the project that is hidden (like the back side of a concrete countertop).

Step 4 – Variable Speed Polisher

• A variable speed wet polisher is a versatile tool that can be used on any kind of decorative concrete work, and can also be used on glass or other stone work.
• The Alpha polisher shown uses normal wall power (110V in USA) and should be plugged into a GFCI. The GFCI a breaker that will stop power to the tool if the risk of electrocution is present.
• The water feed line is just like a normal gardening hose and threads onto a standard spout. There is a valve that controls the rate that the water is fed through the center of the arbor. In some polishers, the water feed line is actually cooling the bearings inside the tool, and running it dry can toast the bearings.

Step 5 – Types of Polishing Pads

• Soft Pads – Require a rubber backer that screws onto the polisher. Soft pads are better for beginners because they’re more forgiving. They’re also able to polish contoured surfaces. Usually used with a water-fed concrete polisher.
• Rigid Pads – Require a quick-release mechanism that attaches to the polisher. Rigid pads polish more quickly than soft pads, but they can also gouge the surface if the pad isn’t held perfectly flat. Usually used with a water-fed concrete polisher.
• Wet / Dry Pads – Require a quick-release mechanism, but unlike other pads, these are safe to use on a high speed angle grinder.

Step 6 – Wet Polishing Preparation

• Have a good idea of what you want to achieve before beginning the polishing process. It’s always possible to remove more material, but you can’t put it back, so work carefully.
• Wear rubber gloves
• Consider wearing a rubber apron and rubber boots.
• Elevate the piece on scrap 2″ foam.
• Polish outdoors, in the shade if possible, or indoors with a polishing table.
• Build a polishing table (sloped table covered with a plastic tarp, 6″ high walls, water drains to a plastic bin, pump to recirculate water, plumbing for water hose valves).

Step 7 – Initial Polish

• For a ground finish, start with the lowest grit pad you have, usually 60 grit. Polish the piece evenly, until a uniform amount of aggregate is exposed, then continue up to the next pad.
• For a light polish, start with mid-range pad, like a 300. You can always remove more material, but you can’t go back, so be careful not to start too low if you don’t want a fully ground finish.
• Tape off anywhere you don’t want to polish with a few layers of masking tape.

Step 8 – How to Polish

• Turn on the water feed.
• Lift the polisher above the surface and turn it on.
• Lower the polisher onto the concrete and let the weight of the tool do the work. Keep the pad as flat as possible.
• Move around the piece evenly, in circular motions. Don’t start or stop in one place for too long.
• If you have a large area to polish, focus on small sections rather than trying to do too much at once.
• Progress to the next pad when the surface is uniformly polished.

Step 9 – Fill Holes with Slurry

• Halfway through the polishing piece (around 400-grit), fill the exposed holes with slurry (cement paste, pigment, and water).
• Resume polishing after the slurry has dried for a day.
• Read the How-To Slurry Guide for more information.