Troubleshooting Guide - Lime Plaster failing/coming off background

If you are experiencing Lime Plaster failing or coming off the background, please consider the following:

1)      Inappropriate background – It is important that lime plasters/renders have both a physical and a suction bond with the background. It is not appropriate to plaster/render over cement, gypsum or modern paints as these will often have a closed texture and in these circumstances, it is unlikely that the plaster/render will have the longevity that is expected of it.

2)      Exposure to heat prior to carbonation – Drying and carbonation are two different processes, just because a plaster/render is dry it does not follow that it has carbonated. Drying is just the process of moisture leaving the plaster/render, whereas carbonation is the absorption of CO2 from the atmosphere and this is how the mortar gains its strength. In carbonation of lime can only take place in the presence of water. Especially a problem internally where plasters can be exposed to central heating, or externally in the height of summer this can make moisture control within the plaster very difficult e.g. internal ceilings where underfloor heating is installed on the floor immediately above. This can cause extreme shrinkage and lead to delamination and separation from the background. 

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.

The reason for the failure should be identified before any remedial work takes place so that the problem is not repeated. Affected areas of plaster/render should be raked out and reapplied in accordance with the manufacturer's guidance.

As well as providing training courses and producing the instructional ‘The Lime Handbook’, Ty-Mawr does provide an on-site supervision and advice service that can be requested.