You now have a finished kitchen concrete countertop and although you could place it in position on top of the base cabinets, weI highly recommend that you grind and polish the surface.
Side Note: For some reason, which I am at a loss to explain, when we deal with wood we finish the surface by sanding it. When we deal with concrete we finish the surface by grinding it and/or polishing it. It is basically the identical process, using very similar tools.
Grinding and polishing does a number of things to the aesthetics and functionality of the countertop:
- Grinding will expose some of the sand and aggregate which will give the concrete countertop a "life".
- By raising the patterns in the concrete any staining that may occur during normal use will be much harder to see.
- The countertop will be flatter, as any high spots will be leveled.
- Any surface problems with the countertop such as water spots, which are not uncommon, will vanish.
Note: You should consider doing the grinding, providing you have used our recipe for the concrete, about 8 to 10 days after the pour.
Safety: Wear goggles, ear plugs, rubber boots and make sure that your electrical tools are plugged into a GFCI circuit.
Note: Grinding is one of the messiest parts of creating the concrete countertop. Grinding concrete requires a continuous flow of clean water. This water will cover your workbench and end up on the floor.
Note: Grinding, like many other workshop processes, requires some practice to get it right. No one can explain how much pressure to apply, or the exact speed of movement that works right for the operator. If you have never used a grinder on concrete, I highly recommend that you practice on a test piece prior to undertaking the grinding of your finished concrete countertop.
Concrete countertop grinding techniques
The techniques used with an orbital sander are the same techniques used with a concrete grinder.
- Allow the grinder’s diamond pad to do the work. You do not have to push hard on the grinder to have the diamond pad remove the surface of the concrete.
- The diamond grinding pad should sit flat on the surface of the concrete. If you angle the pad you will see noticeable swirls in the concrete.
- Grind in all four directions and do not allow the grinder to sit in one spot it must be continually moving.
- Do not try to over reach the area you are grinding. Always work on areas that are comfortable, then stop the grinder and reposition yourself to tackle additional areas.
- When grinding concrete it is imperative that there is sufficient water under the diamond grinding pad.
Clean the top of the countertop using clean water, then using a squeegee remove the water, which in turn will remove any dust, dirt and particles that may be on the surface of the concrete.
This is another situation where some experience makes a big difference and that is choosing the grit of the first diamond grinding pad to use.
The courser the grit of the first grinding pad chosen, the more sand and aggregate you will expose. If you want to expose as much sand and aggregate as possible choose a 50 or 100 grit diamond pad. If you would prefer a more subtle look, less sand and aggregate exposed, then start the grinding process with a 200 grit pad.
Attach the diamond pad that you have chosen to the grinder. Plug the grinder into the GFCI circuit and turn on the water supply. Make sure your safety goggles and ear plugs are in place and commence the grinding process.
Grind the entire surface, including the exposed sides, with that diamond pad, when you believe you have completed that level of grinding, stop the grinder and turn the water off. Using the squeegee remove the excess water and grit from the surface of the concrete countertop and inspect your work. Note any spots that require additional grinding to obtain a uniform finish. Re-work the surface grinding and removing the water and grit with the squeegee until you are completely satisfied with the grinding process and that you have a uniform finish over the entire concrete countertop.
Change the diamond grinding pad to the next level up in fineness. As examples; if you started with a 50 grit your next grit would be 100. If you started with a 100 grit your next grit would be 200.
Grind the entire surface using the next finest diamond grit pad in the same manner as you did in Step 3. Remember to use the squeegee often to remove the water and grit that is left on the surface of the concrete countertop.
Repeat the Step 4 grinding process increasing the grit fineness until you have used the 800 grit diamond pad.
Note: It may be necessary to use diamond sanding blocks to get into the exposed inside corners of the hole for the sink. Follow the same procedure as you did with the grinder. Start with the course diamond sanding blocks (the same grit that you used for the grinder) and proceed using finer sanding blocks, finishing with the same grit in both cases.
Note: Someone who has little experience grinding concrete can expect to take a couple of days completing the entire grinding process.
How to Make Concrete Countertops - Index