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Rendering damp Walls
Many older properties suffer from damp problems and this is made a lot worse when masonry paint has been used or a hard render applied. Older buildings need to breathe and the way they deal with moisture is through natural expansion and contraction. Rendering damp walls with s hard cement render will exacerbate the damp problems. Some renders are not suitable for old properties because they do not allow the building substrata to breathe and rid itself of condensation and other problems associated with damp. Damp and cold walls can deteriorate and may also mean that your heating bills are much higher than they need to be. Traditionally, older properties were treated with a softer lime render using suitably aged lime putty and because the render was soft it allowed the substrata to breathe and prevented a buildup of damp in the walls. When old properties have unsuitable rendering, damp walls are the result.
Unsuitable Renders
Contrary to tradition there has been a tendency for some years to refurbish older buildings with hard rendering made from impermeable materials that are more suited to modern buildings with cavity wall insulation and different substrata. Rendering damp walls with hard cement and a coating of masonry paint hinders the natural movement of old buildings and stops it from ridding itself of condensation and dampness caused by bad weather. Rendering damp walls in this way can result in cracked and peeling renders and even damper walls. Traditionally older buildings were refurbished with a softer render produced from lime putty, which was used for the mortar in a lime wash.
Lime Renders
Traditional soft lime renders are porous and this means that the building can breathe which reduces cracking problems and generally eliminates the problem of damp walls. Once a lime render is mixed it should be left to stand for several days before it is applied to the building as this will reduce the chances that the mortar will crack while it is curing. If you are having problems, check out the existing rendering, damp walls are often the result of a hard render, In order to stop the damp from building up in your exterior walls you may need to have the existing render removed and a softer, lime render applied. You should spray walls with water about half an hour before you add a coat of lime render as this helps the render to better adhere to the surface of the wall. If the weather is very warm then you may also need to spray the walls with water after the layer has been applied.
Use a Lime Wash
You need to wait a few days between coats to give the lime mix time to harden. It is not a good idea to use mortar paint on a lime render because this can prevent the substrata from breathing and cause further damp problems. A lime wash containing some linseed oil will still allow the building to breathe and will help in shedding excess rainwater, which is not possible with harder rendering, damp walls are often the result.
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