Over time the mortar joints in between bricks will require re-pointing, particularly where it in an exposed position or has been subject to leaking gutters and overflows.
Worn pointing can lead to damp problems internally, frost damage to the bricks and in really bad cases the wall can become unstable! Re-pointing brickwork can be carried out relatively easily, but scaffolding will be required for higher areas.
1) Dig out
Firstly the area of wall that needs new re-pointing will need the existing joints raked out to a depth of approximately 15 millimetres. This can be carried out with an old screw driver and a hammer to dig it out, or alternatively you can buy a special mortar rake which is easier to use. You need to do this so that the new mortar has enough brickwork to stick to, otherwise the new pointing will crack and fall out of.
Next you need to dampen the area with a wet brush. This will stop the brickwork absorbing too much water from the mortar as it dries.
3) Mix mortar
Do be careful about the mix of mortar you use. The new mortar should not be too weak with too much sand or too hard with too much cement. For most post 1945 walls a mix of three part sand to one part cement will be satisfactory. This can be bought in ready made bags.
However, if too hard a mix is used on an older house it may cause cracking, as the original mortar will have been softer and be able to flex a little. In older houses lime was used which makes the mortar softer, so this should be added to the mix if repointing an older wall. Do experiment with mixes; colour additives can be used so that the new pointing matches the existing mortar.
4) Hawk and trowel
Once you have your mortar mix which should be workable yet firm, using a board known as a hawk and trowel, fill in the vertical joints first and then the horizontal joints. Hold the hawk against the wall directly beneath horizontal joints and push mortar into the bed with the pointing trowel.
Be careful and try to not get too much mortar on the brickwork, if you do, use a soft brush to remove the unwanted particles. Wait until the mortar is beginning to set before shaping it.
You will want to match the existing pointing. There are different joints but the most common is a flush joint where the mortar is flush with the brickwork.
This is achieved by drawing a strip of wood about 12mm wide, 6mm thick and 100mm long along the joints after the mortar has started to go off. This is probably the easiest finish for a new diyer to achieve.
For more information visit the Landmark Surveyors website here.