Mortar joints in masonry are one of the few parts of a building which are not deigned to be permanent. Properly applied mortar should last for 50 to 100 years, but the time will inevitably come when moisture, temperature changes, vibration and other deterioration make necessary the repairing and replacing mortar joints (also referred to as tuckpointing).
The job of repointing is much more difficult than the average homeowner thinks it is. Joints must be properly prepared, new mortar must match the old in color, texture and hardness, and the joint must carefully be filled such that the mortar adheres correctly. Done by someone inexperienced, repointing can cause further damage to masonry and will probably need to be redone soon.
Repointing projects are best done during mild weather; between 40 and 95 degrees F, and during hotter weather, walls need to be covered in burlap or tarps while mortar sets.
When to Repoint
Repointing is usually associated with some noticeable signs of masonry deterioration, like mortar disintegration, cracking mortar joints, bricks that are loose, plaster damage, or damp walls. Many such problems can’t be solved just by repointing, and the root cause needs to be determined and fixed or repointing will just have to done over and over again, wasting your money and time. See our page on masonry deterioration.
A good rule of thumb is mortar that is firm and not eroded more than a third of an inch from the masonry’s face should be left as it is. What should be repointed?
- Cracked joints, where hairline width or larger crack lines have appeared in the mortar
- Separated joints, where mortar and masonry have a gap between them, or loose mortar is sitting in the joint
- Open joints, where mortar is eroded deeply, or fallen out
It is recommended to only repoint the parts of the structure that are need, rather than the whole wall for instance. Finer joints in brick or stone are particularly hard to repoint, since the removal of old mortar from them is tricky, and could end up being more harmful than leaving the old mortar as it is, except where obvious signs of spalling are present.
Your next step will be to choose a mortar type that properly matches the existing mortar.
Photo by Jon Knowles, Creative Commons Attribution License