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  • What is Eroded Mortar or Pointing?

    13th December 2017

    What is Eroded Mortar or Pointing?

    What is pointing?

    Pointing is the mortar between the bricks or stones in a wall. Over time either the mortar or the brick/stone itself can erode. Areas of eroded mortar can be a source of water ingress potentially leading to damp within the property. More interestingly repointing that has been done incorrectly can be just as bad.

     

    How does it erode?

    Moisture naturally enters the bricks and mortar and evaporates. This process causes the materials to expand and contract. Over time, this continual process causes erosion where bits of the mortar erode or crumble away.

     

    Repairs – Repointing or Patching

    There are two options for repairing the pointing.

    1. Patching (Tuck Pointing) – the old mortar is patched over without first removing the crumbling sections. This is not a long-term repair as the bond between the old and new mortar layers is weak.

    2. Repointing – the eroded mortar is removed to provide a clean brick/stone surface and new mortar is put back in place.

    Patching is quicker and so you’ll get a much cheaper price as it is far easier for your builder. However, you’ll be asking them back in a few years to replace all the mortar that has fallen off and to replace damaged bricks or stone where the wrong mortar is used.

     

    What types of mortar are there?

    There are two main types of mortar used in the construction of houses. Lime and cement.

    Lime mortar is used in older buildings which typically have solid walls. This mortar was very common in properties built before 1930 as it allows moisture to freely move through it and evaporate from the surface. By allowing the moisture to escape through it it prevents damage to the wall (spalling) or damp in the property.

    Cement – was first invented in 1794 by Joseph Aspdin and became more popular than lime mortar by 1930. It sets harder and quicker than lime mortar allowing faster construction which resulted in its popularity. It is also far more water resistant.

     

    What type of mortar should be used for repointing?

    Very simple – you should use the same type of mortar for repointing as the one that was used originally. It might appear to make sense to use regular cement in all cases – it is easier to apply and sets faster and harder with better water resistance.

    But a solid brick or stone wall, built with a lime mortar, needs to breathe. Lime is breathable as it allows the moisture to evaporate through it. Cement is not. Cement traps water in the building which either escapes through the internal walls causing damp or freezes in the brick in winter causing damage (spalling). Where cement has been applied to a wall that requires lime mortar a decision needs to be made. Will it cause more damage to leave the mortar (resulting in damp and/or erosion) or more damage to the brick/stone by removing it?

    Cement can be used on modern properties because the bricks have been developed to be stronger and more resistant to water. They are also designed to keep water out rather than to breathe.

     

    Below is a good example of damp caused by using the incorrect mortar (Source: Peter Ward)