The individual concrete blocks in a wall can become damaged in a variety of ways. A basement wall might develop a water leak or a garage wall might get bumped by a car. How to remove and replace a concrete block from a wall depends on the type of block involved. Most concrete blocks are some type of cinder block, with hollow interior spaces. Replacing a cinder block differs greatly from replacing a solid block.
Drill a pattern of holes into the block with a masonry bit. For most cinder blocks, drill four or five columns of three holes spread evenly across the face of the block. Expand or contract that pattern for bigger or smaller blocks. If you encounter continued resistance through the width of the block, the block is a solid block and not a cinder block. In this case, skip to Step 7.
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Demolish the cinder block with a hand sledge hammer and a cold chisel. The holes drilled in Step 1 make this task easier. Remove any debris and chip away the mortar clinging to the surrounding blocks.
Sweep the newly formed gap in the wall with a hand broom.
Mix a batch of mortar in a bucket or tub, following the manufacturer's directions.
Spread a fresh bed of mortar on the bottom of the gap with a masonry trowel, matching the thickness of the existing mortar in the wall. Put down two lines of mortar on the sides of the block, alongside the corners, and spread a layer of mortar across the top of the block, so all layers match the thickness of the existing mortar.
Place the replacement block into the wall. Draw the trowel across the face of the wall to scrape away excess mortar, and sculpt the wet mortar to match the old mortar with a jointing tool. Sklp Steps 7 and 8.
Remove solid blocks by chipping out the mortar surrounding the block with light taps with the hammer and chisel. When the block is loose enough, pull it out by hand.
Replace the solid concrete block by following the same procedure described in Steps 5 and 6, with the exception that the sides of the block should be covered by a single layer of mortar, instead of the two lines.