Whether you colour the concrete or toss in additives such as glass, the concrete making up your concrete countertop will still cure dull, and remain so unless you shine it to a polish. Polishing your concrete countertop is as simple as applying a series of wet sanding pads. Each pad helps to smooth out the concrete; removing the slightest imperfection until the countertop begins to shine. To maintain the shine, you'll need to apply a protective layer of concrete sealer. The seal forms a wear layer, absorbing the scratches or dings that can dull the shine. The process takes time, but the result is a glossy finish that transforms the dull concrete countertop into a shining, attention-grabbing centrepiece.
- Skill level:
Things you need
- PH-neutral cleanser
- Nylon scrub brush
- Orbital sander
- Rigid backer pad
- Polishing pads, 400-3,000 grit
- Wet/dry sandpaper 400-3,000 grit
- Concrete sealant
Clean the countertop of any dirt or debris using a pH-neutral cleanser and warm water with a sponge or nylon scrub brush. Rinse the cleanser off with clean water.
Use an orbital sander to polish a shine into the countertop. Attach a rigid backer pad to the sander to hold the polishing pads horizontal while polishing the countertop, then attach a 400-grit pad to the backer pad. Saturate the concrete surface with water using a damp cloth. The water will wet the concrete surface to prevent dust from rising as you use the pads. Turn on the sander and then place the pad onto one of the countertop surface corners. Keep the countertop saturated with the water.
Run the pad in rows along the countertop to smooth the counter, removing any irregularities in the surface. Move the sander in small circles, keeping the pad horizontal to prevent creating swirls in the concrete finish. After grinding the surface you'll notice a series of pinholes in the countertop.
Use concrete slurry created from thin concrete mixed in a bucket to the consistency of toothpaste to fill in the pinholes. Spread the slurry over the countertop using a rubber-gloved hand, working it into the pinholes. Scrape the slurry along the top using a plastic putty knife, then allow it to set overnight. Polish the slurry with the 400-grit pad again to remove the layer from the countertop, leaving the holes filled.
Switch the pad to 800-grit and repeat the process of running the pad across the countertop surface, smoothing the concrete still further. Switch again to 1,500-grit and run the sander across the countertop a third time, after which the counter will develop a slight shine.
Switch to a 3,000-grit pad for the final run across the countertop to increase the shine of the concrete to a gloss. Turn off the sander and then wipe down the countertop with a damp cloth to remove any sanding residue.
Polish the countertop edges using wet/dry sandpaper on handheld blocks following the same procedure used with the top of the counter, as well as the same sandpaper grits. Keep the sandpaper wet to keep down concrete dust as you work, then wipe the countertop after achieving the glossy finish with a damp cloth. Allow the countertop to dry overnight.
Brush a layer of concrete sealant onto the countertop to protect the glossy finish from scratches and stains. Use a paintbrush to apply the sealant in even rows, covering the countertop with a moderate layer of the sealer. Allow the sealer to sit and penetrate the counter for about two hours, and then brush on a second lighter layer to make sure you covered the counter's entire surface. Wait 24 hours before using the countertop normally.
Tips and warnings
- Make sure you use a GFCI electrical socket when working with a wet surface to make sure any electrical faults in your sander will immediately result in an interruption of the flow of electricity rather than in an electrical shock.
- Wait at least 21 days after pouring a new countertop in place before polishing it to allow the countertop to cure completely after installation.
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