Damage to cinder blocks in foundations can cause water to leak into your home and possibly cause damage to the rest of the foundation. Cinderblocks are a common material for foundations but are also used for garages and other structures. Though they are strong and durable they can break or crack. Quite often water sitting on the blocks freezes repeatedly. This will weaken the block until it eventually breaks.
If you have a broken cinder block in a wall, it can be easily replaced if simply patching it is not an option. It is a good idea to replace broken blocks to prevent water damage or heat loss. If the block is in a visible place you may also want to replace it for aesthetic reasons. Before you begin make sure there are no wires or pipes running through the wall where you are removing the block. This is quite rare however, because in most cinder block walls the blocks are staggered for extra strength. If for some reason you do find a pipe or wire running through the wall you should consult with an electrician or a plumber before you proceed. The first step in replacing a cinder block is removing the old block. Use a cold chisel or a hammer to chip out the entire block. Be careful that you do not damage any of the surrounding blocks or you may end up replacing them as well. Pull out all broken pieces of cinder block and chip away as much of the mortar as possible. Clear out the space as much as you can because you will need to fit the new block in the space along with mortar to secure the block. If you run into a bond beam you may have some difficulty. Bond beams are often placed on top of a row of cinder blocks for extra stability as the wall is built. They are often made of metal and run the entire length of the wall. If you find one you can attempt to remove the mortar from the bar. This may be difficult. Mortar tends to stick to bond beams very strongly and it cannot be removed. If you cannot remove the mortar you will need to use bolt cutters to remove that section of the bond beam. This will not compromise the integrity of your wall. Once you have the hole cleaned out and ready to go you should mix up a small batch of mortar. You can buy this at any home improvement store. Apply the mortar to all surface areas of the open space. Apply more than you think you will need. You may also wish to use a spacing shim to keep the new block level with the rest of the blocks in the wall. Place the proper sized shim on top of the block at the bottom of your open hole. Now you are ready to insert the new cinder block. Once you have it inserted check for placement and fill in more mortar into any spaces you see. Be sure to pack it in as tightly as you can. You can then finish up with a mason's striking tool. This tool is used to make a smooth finish around the block. If you have a wall that is viewable from both sides, don't forget to use the striking tool on both sides of the wall.
