Re-pointing...

With exposure to weathering (wind, rain, frost etc), the mortar holding masonry (bricks or stone) together on an external wall will often start to crumble away and fall out. On older properties, the pointing maybe harder mortar than the bonding mortar, so once this is dislodged, the softer bonding mortar will become exposed and wear away quite quickly. Likewise, the faces of bricks and stones can start to crumble (spalling) and fall away due to weathering. It is important to repair the pointing and masonry otherwise water will increasingly penetrate into the wall leading to further damage.

Spalling on a brick wall.

If the damage is limited to a small area, just that area can be repaired be replacing damaged masonry and re-pointing. However this re-pointed area will tend to then stand out. Generally a whole wall face will have weathered in a similar way, so the whole wall will need re-pointing at the same time.

The type of mortar used for re-pointing is important. There are basically two types of mortar, lime based mortar and cement based mortar.

Lime based mortars are normally used in the restoration of older buildings. These buildings usually have solid walls, with no cavity, and are often built on insubstantial foundations. They are therefore liable to settlement and movement associated with seasonal changes in ground
conditions. Lime mortar is softer and weaker than the stone or brick which it bonds and is therefore able to accommodate slight movements caused by settlement or temperature changes without significant cracking. Lime mortar is permeable and allows evaporation of rising and penetrating damp from within the wall. It is this permeability, or 'breathing', which helps to keep the building dry inside without a damp proof course or chemical treatments.

Cement based mortars are normally used in the restoration of newer buildings. These buildings normally have cavity walls and built on substantial foundations. They are therefore less liable to settlement and movement associated with seasonal changes in ground conditions. Compared with lime mortars, cement based mortars are harder and more brittle, much less porous and sometimes completely water-proof.

The use of cement based mortars in traditionally built building can be damaging. Cement pointing is harder than soft brick or stone used in traditional buildings and is too rigid to accommodate settlement or movement in the wall and can crack. Further damage can be caused by rainwater seeping into the cracks in the pointing and around the edges of the stones. Because the cement based mortar is not permeable this moisture cannot evaporate from the mortar joint once rain stops. Instead it is forced to evaporate through the face of the brick or stone and soluble salts present in the water crystallise in the surface layers of the masonry leading to crumbling and decay. This is sometimes so severe that the entire face of the stone is lost and the hard cement pointing is left standing proud. Further rainwater is trapped and the decay continues. The concentration of trapped water in the masonry also increases its susceptibility to frost damage in winter.

The most appropriate choice of mortar to use will depend on the extent of cement based materials present, the Customers preferences and any listing or conservation restraints placed on the building.

| Services  ...