Troubleshooting Guide - Lime Mortar Leaching

Lime Mortar Leaching has two possible causes:

1. Exposure of pointing to rain prior to carbonation can cause lime to leach out of the pointing. It is important therefore that all mortars are protected from the elements until they have a chance to carbonate.
2.  If fat lime is used for building works it can take years for the lime in the centre of the wall to carbonate. In certain situations, such as freestanding walls, if water is allowed to percolate into the body of the wall, then ‘free lime’ can leach out of the pointing and down the face of the wall. This is identifiable as a white calcareous deposit.

 Resolution

Ty-Mawr products use the highest quality British quicklime and are produced under the strictest of conditions in accordance with ISO9001:2000. It must be remembered that the carbonation of lime is a very simple chemical reaction and there is very little to go wrong with it, problems are usually caused by the inappropriate selection or use of materials.

If leaching does occur it is important to ascertain why it has occurred. If the leaching has been caused by exposure to rain, then the pointing will likely fail when exposed to winter weather. It should be raked out and replaced.

If leaching is caused by water percolating through the body of the wall then the caused of the leaching should be rectified e.g. sufficient capping stones placed upon freestanding walls to shed water clear of the wall. The condition of the wall should then be assessed to see the extent of any damage caused by the leaching, and appropriate remedial action is taken if so required.   Then the white calcareous deposit can be removed from the face of the wall by using a wire brush. A weak acid can be used CAREFULLY if the leaching cannot be removed by mechanical means from the face of the masonry or brick.

Ty-Mawr does provide an on-site supervision and an advice service that can be requested.