Sadly, many old buildings that have survived for centuries in good condition go into steep decline after they are “modernised”.
When an old building was originally constructed, the pointing (joints between stones or bricks) would have been created using a mixture of lime and sand. This allowed moisture to evaporate through the mortar joints rather than through the stone or brick itself. When water passes through any material and evaporates, it deposits dissolved salts, which crystallise as efflorescence. Lime mortar encourages moisture to evaporate from the surface of the pointing, so efflorescent salts will crystallise in the mortar joints. Eventually this does damage the pointing, but this can be raked out and replaced every fifty years or so.
In contrast, cement based mortar is brittle and impermeable to moisture. If an old building is repointed with cement based mortar, it causes serious problems for the building:
- Any water which does pass through the cement will cause it to crack, leaving a route for rainwater to get into the wall.
- The wall is now damp but is struggling to “breathe” because of the impermeable cement, so water is trapped in the wall, making the wall cold and prone to condensation inside the property.
- The moisture which does manage to escape will be forced through the stone instead of the pointing. As this happens, the moisture can expand and force the face off the stone, causing severe damage to stone or brickwork that is extremely costly to repair.
Cement-based repointing has caused untold damage to historic stone and brick buildings.
If you wander down the main street in the village of Cromford, you can see the contrast between the old millworkers cottages that have been re-pointed with cement mortar and those that have been left alone or re-pointed with lime.
In this house, new cement mortar is not only cracking and falling off the wall, but you can also see the damage it has caused to the stonework.
In contrast, this cottage below still has lime mortar and the stonework is healthy.
Unfortunately, if your old building has been re-pointed with cement based mortar, the only long term solution is to rake out the mortar and re-point with lime. This is one of our main specialisms and we do a beautiful job and take real pride in our work. If you are worried that your house has been pointed in the wrong materials, do get in touch for a no obligation chat.