Polishing + Slurrying the Countertop

Q1: Do I have to polish my concrete countertop?

Not necessarily. If you like the results straight out of the mold, you don't need to polish at all. Decide what countertop surface suits your project and your aesthetic.  If you are trying to show exposed aggregates and decorative inserts, polishing will be necessary.

Q2: How do I achieve a high-polished look?

You can achieve a high polish by carefully polishing with the Diamond Polishing Pads (50, 100, 200, 400, 800, and 1500 grit). First use the 50-grit pad, then the 100, 200, 400, 800, and 1500, just as marble and granite fabricators do. The 50-grit pad is the most aggressive and should be used to achieve the desired exposure of aggregate. The range of grits, from 100 to 1500, in conjunction with CHENG Concrete Countertop Sealer and CHENG Concrete Countertop Wax, will polish the surface out to a high sheen. For more information, refer to "Grinding and Polishing," pages 136-142, in Concrete Countertops, or "Polish and Slurry," pages 74-81, in Concrete Countertops Made Simple Book and DVD Guide.

If you are a concrete professional in learning how to achieve our proprietary, mirror-like CHENG Geocrete™ finish, you can learn that trade secret and many other advanced techniques at our Advanced Countertop Design Training.

Q3: When, during the process, do I polish the concrete countertop?

Polishing, should wait until the concrete is well cured. If the concrete is too soft, it will appear dull and be more susceptible to scratch and swirl marks during polishing. When using either the CHENG Pro-Formula Concrete Countertop Mix or the NeoMix Original Products, we recommend allowing 4 full days (at 80ºF) of curing before attempting to polish your countertops. Concrete that does NOT include these additives should be given an additional 14 days to cure before polishing.

Concrete over a month old is very hard, and polishing at this point will require more effort and a lot of diamond pads! For more information on polishing, refer to "Grinding and Polishing," pages 136-142, in Concrete Countertops, or "Polish and Slurry," pages 74-81, in Concrete Countertops Made Simple Book and DVD Guide.

Q4: Why do I need hand-finishing pads?

After de-molding a countertop, many burrs and rough spots will appear on the underside edges and corners of your countertop. Because it would be too severe and uncontrollable to hone these spots with a polisher, a Hand-Held Diamond Polishing Pad is the best tool to smooth out these areas. The edge of a sink knockout or other curved and delicate details will require a similar approach. Refer to "Grinding and Polishing," pages 136-142, in Concrete Countertops, or "Polish and Slurry," pages 74-81, in Concrete Countertops Made Simple Book and DVD Guide.

Q5: What type of polisher equipment do I need?

Because polishing at different speeds will be needed, the most important feature of a polisher is the ability to polish at variable speeds. Available in either electric or pneumatic, a polisher should be able to operate between 800-3000 RPMs. Since water is required to polish, a built-in water feed, double-insulated motor and ground fault interrupter, as a safety precaution, are all requirements of an acceptable polisher.

Lastly, if you are interested in using CHENG Polishing Pads, make sure that your polisher has a 5/8" arbor (most standard polishers do) in order to fit CHENG Polishing Pad Holders. The variable speed wet polisher used in our shop is available in the Equipment Section of the Online Store. For more information on grinding and polishing, refer to "Grinding and Polishing," pages 136-142, in Concrete Countertops, or "Polish and Slurry," pages 74-81, in Concrete Countertops Made Simple Book and DVD Guide.

NOTE: Be aware of metal-angle grinders that grind at high speeds that look the same as the polishers we use. These polishers can damage the pad holder or cause excessive wear to your diamond pads.

Q6: Do I need every grit of concrete polishing pad for my project?

Polishing a concrete countertop is very similar in principle to sanding wood. Start with the lowest grit polishing pad and work your way up through each subsequent grit to ensure minimal swirl, or sanding marks. Given this, we recommend the following polishing pad sequence when exposing aggregate: 50, 100, 200, 400, then slurry, 400, 800, and finally 1500.

When not exposing aggregates, we recommend: 800, then slurry, 800, and 1500. For more information on grinding and polishing, refer to the "Grinding and Polishing," pages 136-142, in Concrete Countertops, or "Polish and Slurry," pages 74-81, in Concrete Countertops Made Simple Book and DVD Guide.

Q7: At what speed do I use each grit of concrete polishing pads?

Each polishing pad grit requires a different polishing speed because a concrete countertop can be "over-ground," or over-polished, leaving excessive swirl marks if the polishing speeds are too high. Generally speaking, the lower the grit, the lower the polishing speed; the higher the grit, the higher the polishing speed.

We recommend 800 RPMs for 50 grit, 1000 RPMs for 100 grit, 1500 RPMs for 200 grit, 2000 RPMs for 400 grit, 2500 RPMs for 800 grit and 3000 RPMs for 1500 grit. For more information on grinding and polishing, refer to "Grinding and Polishing", pages 136-142, in Concrete Countertops, or "Polish and Slurry," pages 74-81, in Concrete Countertops Made Simple Book and DVD Guide.

Q8: My concrete countertops have a few small voids (created by trapped air). What is the best way to fill them?

Voids are best filled with a color-matched slurry, containing cement, pigment and an acrylic bonding agent. Large voids should be filled with slurry containing sand while smaller voids should be filled with slurry containing NO sand at all, such as our CHENG Pro-Formula Acrylic Slurry. The CHENG Concrete Densifying Agent is an admixture that drastically minimizes the air bubbles that develop when mixing the concrete.

Q9: When do I apply the slurry?

If necessary, a slurry coat is applied to the concrete countertop after de-molding. We recommend 4 days of curing in the mold if you are using the CHENG Pro-Formula Concrete Countertop Mix. Prior to slurrying, the countertop should be polished, at least minimally, to expose all potential voids prior to filling. If you are exposing aggregate in your countertop, work your way up starting from 50 grit through 800 grit diamond pads before applying slurry.

If you are NOT exposing aggregate, polish your countertop with an 800 grit diamond pad before applying slurry. For more information on polishing, refer to "Grinding and Polishing", pages 136-142, in Concrete Countertops, or "Polish and Slurry," pages 74-81, in Concrete Countertops Made Simple Book and DVD Guide.

Q10: How long do I wait before I continue polishing after slurrying?

After applying CHENG Pro-Formula Acrylic Slurry, allow 24 hours before returning to final polish. Remember to begin final polish with the same grit diamond pad that was last used before slurrying. Larger voids might require multiple applications of slurry.

Follow the same steps as outlined until all voids are filled in as desired. For more information on grinding and polishing, refer to "Grinding and Polishing", pages 136-142, in Concrete Countertops, or "Polish and Slurry," pages 74-81, in Concrete Countertops Made Simple Book and DVD Guide.

Q11: I just opened my CHENG Pro-Formula Acrylic Slurry—why doesn't it look like my countertop color?

The contents of CHENG Pro-Formula Acrylic Slurry may not look like the color of the countertop at first. Because we use powdered pigments that are all blends (i.e. blue plus yellow make green), the contents of the slurry kit may appear to be very different until water is added. When the contents of the NeoMix Slurry Kit are mixed with water, the proper color will be achieved.

Q12: How do I achieve the "veined/pressed" look in my countertop?

Some fabricators deliberately create voids in their finished concrete, which they then fill with a slurry coat of a different color to create the "veined or pressed" multi-colored surface finish. To achieve this look, your countertop mold should be hand-packed with a stiffer concrete mix and not vibrated. This will produce fairly substantial voids that can then be filled and finished with one or more contrasting colored slurry coats.