Now that the weather is warming up and we are having a few sunny days there will inevitably be calls from customers who have had their walls replastered or skimmed over the autumn and winter months and who are seeing cracks appearing. Due to the nature of plaster, seasonal changes in humidity and temperature can affect the finish, leading to cracks in different areas as the walls and plaster dry out a little. Older and larger properties have this problem more often than new builds where insulation is very efficient and there are no underlying damp problems. If walls remain cold (and perhaps damp) during the winter when they are reskimmed then problems can occur in the spring and summer as the building warms up and dries out, drying the plaster out causing hairline cracks.
People often assume that cracks in plaster are the fault of the plasterer, or jump to the conclusion that there are serious structural problems with their home. Very few people consider the effect of seasonal climate changes on their properties, and often fail to notice factors such as large trees growing close to their property. Large root systems can cause structural damage, but they also provide drainage as the tree draws water out of the ground. Very wet or very dry weather can lead to problems with cracked plaster when the ground underneath is subject to changing groundwater levels. Additionally, people often want to fix cracks in their plaster immediately, thereby leading to further problems caused by a misunderstanding of the causes.
It is advisable to monitor a crack over the course of a full year, and note down temperature and humidity changes alongside information about the progress of the crack. Measure the size of the crack at various points to build up an accurate picture of the movements. Doing this does mean you have to live with the crack for a year, but when the causes of the crack are properly understood it can be repaired in a way that will last, rather than attempting to repair a seasonal crack year on year. When you have built up a picture of the changes in climate in relation to the changes in the crack it will become clear what is causing the crack, and armed with this information you can decide on the best solution for repairing it and making other changes around the property in terms of drainage if needed.
Cracks caused by slow drying plaster can be reskimmed easily, and the problem should not occur again. Recurrent cracks caused by seasonal building changes need a more intensive repair, and depending on the size of the crack this will involve taking some of the surrounding plaster off to create a larger area to work with. By exposing the brickwork you can reveal any cracks in the structure of the building that are manifesting as surface cracks in the plaster. If these cracks in the brick are caused by seasonal changes to the structure of the house the wall can be pinned with a metal mesh that will help to take some of the movement and spread it across a larger area, rather than concentrating all that movement on one small area. Filling a larger area means the elasticity of a larger amount of plaster can accommodate the movement far better than a small amount, so by addressing the structural problem first, then repairing the plaster you can achieve a lasting repair, which is preferable to filling in the same crack year on year when the fill plaster inevitably falls away. Seasonal cracks can be repaired effectively with a little research and understanding of the causes.