How to Repair a Concrete Block


Many houses and other buildings have foundations, walls, and other major structures made from concrete blocks. Concrete blocks, also sometimes called cinder blocks, are block-shaped and made from cured concrete. They are easier to move and rearrange than poured concrete, which is difficult to remove once laid. Seriously damaged concrete blocks must be replaced one at a time, but cracks and chips are simpler to repair.

Things You'll Need

  • Siliconized latex caulk
  • Caulk gun
  • Metal-bristled scrub brush
  • Garden hose
  • Small paint scraper
  • Sledgehammer
  • Small chisel
  • Prepared concrete patch
  • Metal trowel


  • Rub firmly over the cracks, using a scrub brush with stiff metal bristles. Scrub each crack until the loose particles of concrete have been removed. Spray the concrete block with a high-powered garden hose to remove dust and debris. Allow the concrete to dry 24 to 48 hours.

  • Insert the siliconized latex caulk into the caulk gun and remove the cap. Push the tip of the container of caulk as far into the first crack as possible. Press firmly on the trigger of the caulk gun to fill the crack and allow a little overflow at the top.

  • Remove the tip of the caulk from the crack and smooth the overfill along the crack with a gloved finger. Use the side of a small paint scraper to flatten the caulk against the concrete and scrape away the extra caulk with the edge. Fill the remaining cracks and allow them to dry 24 hours.

Chips and Crumbling Areas

  • Chip away any jagged, broken areas from the concrete block, using a sledgehammer and small chisel. Rinse the concrete block thoroughly with a garden hose and allow the block to dry completely for 24 to 48 hours.

  • Open the prepared concrete patch and gather several tbsp. onto a metal trowel. Trowel the concrete patch into and around any chipped or crumbling areas, making a layer about 3/8 inch thick. Wait 30 minutes to an hour until the patch product is set.

  • Apply a second, thicker layer of concrete patch to the chipped or crumbling areas, using the metal trowel. Make this layer thick enough to bring the deteriorated areas level with the good concrete around them. Smooth the surface of the concrete patch with the face of the trowel and allow the patches to dry 48 hours.

Tips & Warnings

  • Use a shade of siliconized latex caulk that closely matches your concrete blocks. Realize that contrasting colors will stand out and look unattractive, so it is worth the effort to find the correct hue.
  • Wear safety glasses and gloves.

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