An angle grinder equipped with a concrete-cutting blade makes straight sharp-edged cuts in a concrete block's surface. An angle grinder's design enables it to cut small square holes in a concrete block; a useful trait when installing electrical outlets in a concrete block wall. A concrete-cutting blade for an angle grinder has a diamond-studded rim with ventilation grooves -- a tile-cutting blade uses diamond studs but does not have the grooves. The grooves carry the concrete dust away from the rim, which prevents dust build-up around the diamond studs and cools the blade.
Layout the cut on the concrete block with a tape measure and pencil. Draw a straight line across the block's surface at the measurement marks with a pencil, using a carpenter's square as a guide.
Put on safety goggles, a dust mask and leather work gloves. Angle grinders throw debris and create a lot of dust while cutting concrete blocks.
Turn on the angle grinder. Hold the angle grinder so its blade faces out and the guard faces up. When cutting, the blade will throw debris back toward the handle and operator. This protects the user if the angle grinder drops or binds in the cut -- the blade will roll the grinder away from the user.
Score the concrete block's surface along the pencil marks with the angle grinder's blade. Work the blade back and forth across the pencil line until the blade creates a 1/8-inch deep groove. Repeat this on each pencil line.
Cut through the concrete block along the score marks with the angle grinder. If cutting straight lines completely across the block's face, cut both outside edges before cutting the center of the line. If cutting a hole in the center of the concrete block, work the angle grinder's blade through the center of each score mark. Once the blade penetrates the center of the score marks, work the blade to the corners of the hole.
Flip the concrete block over. Finish the corner cuts and trim any excess concrete from the cut with the angle grinder on the reverse side of the concrete block. Trimming from the reverse side protects the concrete block's visible surface.