The question of how long a rendering lasts is a complex question because there are so many factors involved. Often, the questions relating to how long rendering lasts often fail to take into account the many problems associated with certain types of rendering and some of the benefits of others.
We will start with the problems associated with cement renders.
- may need replacing a lot sooner than more modern acrylic renders as the former are more inclined to crack and break off, particularly if bottom layers have been allowed to dry out too much or not allowed to dry sufficiently.
- are more liable to shrinkage than either lime or more modern plastic and acrylic renders.
- (if they have a couple of layers of masonry paint over the top) may need to be replaced because it can affect the substrata’s ability to shed moisture. The solution would be for the cement render to be removed and the dampness dealt with by applying either a traditional lime render or one of the more modern specialist applications that are designed to protect against damp.
- are generally far more brittle than lime renders which is why they tend not to last as long before they need replacing.
The benifits of modern renders and traditional lime renders are:
- that modern renders are especially useful on older buildings that are not appropriate for cavity wall insulation.
- that an acrylic render may last for many years as do lime renders. Many old churches and public buildings have lime renders that date back centuries and although some of them might be in a state of disrepair, this is strong evidence to suggest the high durability of traditional lime renders.
Choosing the right render in weather conditions
If you live in an area where there is a significant amount of rain and other bad weather conditions, some renders will not be suitable compared to others. One of the reasons that lime has been used to render old cottages is because it can stand up to excessive weather conditions and will protect the substrata underneath i.e. lime/ calcium oxide (CaO) is dissolved by water molecules forming aqueous calcium hydroxide (Ca(OH)2). This aqueous compound can be turned into solid calcium hydroxide once the rain has abated and the rendered surface is dry.
Some silicone renders are ideal for buildings in areas where the weather is bad as they will protect the bricks from the damp.
Modern applications tend to last longer and often come with a warranty that guarantees the length of time the render should last.
Ways to increase the longevity of renders:
Renders always last longer when the application is put onto a clean wall. If you apply renders to a dirty exterior wall then they may not adhere to the surface properly, which means that pieces can crack and break off, shortening the expected life of that render. Most builders will tell you that unless your exterior walls are properly prepared irrespective of what type of render you use, it will not look as good or last as long as it is supposed to. Most people who want to know the answer to how long does rendering last are concerned about the cost as much as anything else. uired on your home.