What is repointing brick, and does your house need it?

What the pointing actually does

The mortar between your bricks is not glue. On a traditional solid wall it is deliberately softer than the brick itself, so that any movement, salt or moisture is taken by the mortar rather than the brick face. Mortar is the sacrificial layer. It is meant to erode over decades, and it is meant to be replaced.

The joints also shed water. A correctly profiled joint throws rain off the face of the wall. An eroded, recessed or cracked joint holds water against the brick instead, and that water goes somewhere - usually into the wall and eventually into the room behind it.

Why mortar fails

Age and weather do most of it. Wind-driven rain on the south and west elevations wears joints back, frost expands trapped water and pops the surface, and a century of London pollution does the rest.

The bigger cause of premature failure is the wrong material. From the 1950s onwards huge numbers of Victorian houses were repointed in hard cement mortar. Cement is stronger than the soft stock brick around it, so instead of the mortar eroding, the brick face does. That is why so many period terraces have crumbling, blown brick faces alongside perfectly intact cement joints.

How repointing is done properly

The old mortar is raked out by hand, to a depth of at least twice the width of the joint. Hand tools only - an angle grinder is quicker but it widens the joint and chips the brick arises permanently, and you can spot a ground-out wall from across the street forever afterwards.

Fresh mortar is then mixed to suit the wall: lime for pre-1919 and listed properties, a softer cement-lime mix for later brickwork. It is packed into the joint in layers rather than smeared across the face, then finished to the profile the wall originally had - flush, weatherstruck, bucket handle or tuck.

Lime work is then protected while it cures. Hessian, damping down, and keeping sun, frost and driving rain off it for the first few weeks. Skip that step and the mortar never gains strength.

Signs your house needs repointing

Mortar that crumbles or brushes out when you rub it with a finger or a coin. Joints noticeably recessed behind the brick face. Sandy deposits on the ground below the wall. Damp patches inside that appear after rain and follow the weather. Plant growth or moss taking hold in the joints. Cracked or spalled brick faces.

If any of those apply, get it looked at. Repointing is far cheaper than brick replacement, and brick replacement is what you end up doing if you leave it.