Replacing bricks in a cavity wall

With the passing of time, some bricks can start to degrade, either:

  • As the result of poor manufacturer (more common with old brick than modern post War brick)
  • Due to water trapped behind the front face of bricks expanding during freezing conditions causing the face to flake off (known as 'spalling').

Both types of fault are normally restricted to an odd brick 'here and there' on a wall and these can normally be easily replaced.

At other times, a single brick or a number of bricks may need to be replaced where an existing hole in the wall is no longer required - such as where an existing soil pipe or heater vent has been removed.

When cracks across a number of bricks are evident, professional advice may be required to ensure that they are not signs of a bigger problem (such as movement of the foundations).

Replacement bricks

Replacement bricks should be selected to match in colour, texture and size. Now that standard UK bricks are metric, replacements for the old Imperial size (larger) may often only be found at reclamation yards.

It may just be possible to reuse some damaged bricks if removed carefully from the wall, by refitting them with the previously outer face facing inwards, the characteristics of the original brickwork will then be retained.

Queen closerIf replacing a single brick, or a few bricks in a non-load bearing wall and you are short of replacements, it is possible to cut them lengthways using a disc cutter so that you end up with two Queen Closers per brick. These can each be fitted with their good face outwards giving the appearance of two separate bricks.

Removing old bricks

Rack out as much of the mortar from around the brick as possible. On soft mortar use a hook or old screwdriver, alternatively use a 'plugging' chisel and club hammer - start by taking out the vertical joints, then work on the bottom and finally the top joint. Care needs to be taken that hammering does not cause damage to other joints in the wall, lime based mortars are especially susceptible to vibration damage.

If necessary, cut into the mortar beds by drilling a row of holes using a masonry drill bit which is smaller than the thickness of the mortar beds (typically a 6 or 7mm drill). Then use a 'plugging' chisel and club hammer to remove the mortar between the drilled holes.

Take special care when taking out the front part of the mortar to avoid damaging the neighbouring bricks.

Where the original mortar was lime based (i.e. soft), a masonry saw or hacksaw blade may be used once a large enough hole has been created for the blade to fit through - when using a hacksaw blade, use it so that the cut is made on the pull stroke, and wrap the blade with insulation tape to form a hand hold.

TIP: Don't try to speed up the job by using a disc cutter or angle grinder to cut the mortar beds, it is impossible to keep the disc lined up and every miss alignment will damage the neighbouring brick.

If the mortar is very hard and the brick is not going to be reused, it may help to break up the brick while it is in the wall - this can be done using a disc cutter/angle grinder or by drilling into the front face but care needs to be taken to avoid damaging the surrounding bricks.

Once the brick is removed, clean out any mortar remaining in the cavity and on the neighbouring bricks.

Insert the new brick into the cavity to make sure that it fits with no obstructions.

Inserting new bricks

The mortar used to fit the new brick, should be the same type as the rest of the wall, typically either:

  • Lime based - 5:1:1 - sand:lime:cement
  • Cement based - 5:1 - sand:cement

Wet the sides of the bricks in the cavity (this will prevent them sucking the moisture out of the mortar).

Place a bed of mortar on the floor of the cavity and on one side, make sure that it is a little thicker than the original/surrounding bed joints.

Dampen the replacement brick and apply some mortar to the top and to the other end of it.

Keeping the brick level (it may help to hold it on a hawk or piece of board), push it into the opening. As you do so, some mortar should squash out from around the sides of the brick - this is a good sign that enough mortar has been used - if mortar does not squeeze out, the mortar joint is too thin and the brick should be removed and reinserted using more mortar.

Push the brick back so that it sits level with the surrounding bricks and the front face is just proud of the surrounding bricks. Line up the front of the brick with the surrounding ones by using a wooden straight edge across the face both horizontally and vertically.

Use a pointing trowel to compact the mortar around the brick and add more if necessary.

Finally strike or point the mortar around the new brick to match the original finish, or, if the wall is being repointed, scrape out the mortar so that there is room for the repointing.

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