Cracked, broken or frost-damaged bricks are best replaced completely. But make sure that you know what has caused the damage before you attempt to repair it - it may be indicative of a serious problem.
Extensive cracking, for example, may be due to subsidence which requires major attention. It's worth getting specialist advice on brick problems which extend over a significant area, rather than trying to patch the damage. And never attempt to remove more than about 10 bricks, since a large area of unsupported brickwork will need propping while you replace the damaged bricks.
Replacing a small area of damaged bricks is not a particularly difficult task, but there are certain things you will have to bear in mind when doing this. If you are dealing with a cavity wall, you must be careful not to let any large pieces of brick or mortar fall into the cavity; it may create a moisture bridge and cause problems with penetrating damp.
You must also make sure that the replacement bricks match the rest of the brickwork and that the pointing style is consistent with the rest of the wall. If your house is an old one and the brickwork is weathered, use second hand replacements so that the new area doesn't look out of place. You can buy old bricks fairly easily from demolition sites or builders' yards, though you may have to remove the old mortar and clean them before they can be used.
You need mortar for laying the bricks and pointing the joints. For a small amount of brickwork, it's generally easiest to buy a bag of ready-mixed mortar. But make sure this is the type for bricklaying. To remove a damaged brick, start by drilling closely spaced holes into the mortar joints around the edge. You need a masonry bit about 10mm in diameter and a powerful electric drill - preferably one with a hammer action.
Chip away any remaining mortar using a bolster or thin cold chisel and club hammer.
Run the chisel along each side of the brick to work it free and clear of mortar. It may be possible to lever the brick out in one piece, but if not, use the bolster to break it up. This makes it much easier to remove, but again take care that pieces don't drop down the cavity by mistake.
When you have removed the first brick, it is much simpler to prise out any others without too much chipping. But if you are dealing with a solid wall built from two thicknesses of bricks they will still be held by the inner layer and the job is less easy. In this case you will have to break up the bricks with a chisel and club hammer.
Once all the damaged bricks have been removed, clean up the surrounding mortar joints ready for laying the new bricks. After brushing away the loose debris, remove any stubborn mortar with a wire brush. Finally, use a soft brush to get rid of all the dust and dirt. If the area is not cleaned out, you will find that the fresh mortar will not tie in properly.
Dampen the surrounding bricks with water to stop them sucking the water out of your bricklaying mortar too quickly. Spread the dry mortar mix on a board and make a small depression in it so you can slowly add water from the centre. Add dry mix from the outside until all the water is absorbed. Repeat until you have a firm but workable mortar mix.
Use a bricklaying trowel to pick up some of the fresh mortar and spread it along the base of the hole in the wall to a thickness of about 10mm. Then slap a layer of mortar on the top and sides of the first brick and spread it to a similar thickness as in the hole.
Fit the first brick carefully into the wall, making sure that it is flush with the face. Press it firmly into place so that the mortar holds it to the adjacent bricks. Repeat the process until all bricks are in position. This can be quite tricky as you manoeuvre the last brick into place, so make sure there is plenty of mortar in the gap and use the trowel handle to tap the brick into position. Take care not to drop any mortar down the cavity as you do so.
You can use any remaining mortar to fill in large gaps around the new bricks. Leave for a few hours to harden.
Next, mix up some mortar for the pointing, and make good all the mortar joints, pressing it in with the blade of the trowel. Make sure the pointing is consistent with the rest of the wall.
When the mortar has almost dried, clean off any traces of mortar on the bricks by brushing hard with a wire brush. If this fails to remove all the debris, you can get special chemical brickwork cleaner. The solution is extremely corrosive to the skin, so take great care when using it. Brush the solution on and wait until the effervescent action stops. Then wash it off with clean water. Finally, clean up the entire area with a soft brush.
If the surrounding brickwork is fairly old, it may take some time for the new bricks to blend in, even if you have managed to buy replacement bricks from a demolition yard. If this is the case, disguise the area by erecting trellis work over it and planting some climbing plants.
Never allow the plants to attach themselves directly to the wall, however, for although they look attractive, they can cause extensive damage if their roots are allowed to penetrate any loose spots in the pointing.
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