How To Sand Thinset

Tiling bathtub or shower enclosures, kitchen backsplashes, countertops and floors is a favorite pastime of the do-it-yourself-set. But things don't always go as planned, especially if you're new. You can mix thinset to the consistency of peanut butter, but it dries very quickly and can be difficult to apply as thinly as its name suggests. Sanding a too-thick layer of thinset once it dries takes some work, but you can do it.

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Thinset is a mixture of cement, sand and an agent that helps the mixture retain moisture. You apply it between drywall, cement board, a concrete slab or a subfloor and tile. Its purpose is to adhere the tile to its designated surface. Beginning tilers should apply thinset in a very thin coat to the back of their tiles rather than to the walls or floor. It is easier to work with it in much smaller amounts when you're first starting out.

Because thinset contains cement, it dries hard. Sanding it down will take time and effort if you decide to do it by hand. Wrap coarse 24-grit to 80-grit sandpaper around a small wooden block. This allows you to apply more pressure to the sandpaper and helps protect your hand from scrapes. Sand up and down first and then side to side. Wear goggles and a dust mask when you sand thinset to ensure that no flecks get in your eyes and no dust particles reach your lungs. Wipe or vacuum away the dust every few minutes, and thoroughly dust or vacuum the area when finished. You can use water to clean thinset, but make sure the area is completely dry before moving on to the next step.

A black block is basically a shaped chunk of lava rock. Use it to sand thinset the same way you would use a sandpaper-wrapped wooden block. First, sand up and down and then side to side using strong, even pressure. Wipe away the dust every few minutes, or use a hose attachment to vacuum it away. Wear protective goggles and a dust mask.

If you have a fairly large area of thinset that needs sanding, consider using a handheld power grinder. Follow the manufacturer's instructions and start with a coarse-grit sandpaper of 24- to 80-grit. Wipe away or vacuum up the dust before installing your tile. Go over the area again with 80- to 100-grit sandpaper if you will be painting the thinset. Clean it thoroughly of all dust so that your paint will dry smoothly.