Older walls in need for replastering need special handling in any of the following cases:
- Building age: for walls older than a 100 years
- Rising damp: the building has/had rising damp, there are signs (at the bottom of the walls the paint is peeling, flaking or crumbling, there are tide marks or salt deposits etc.) indicating that rising damp might / has been present
- Efflorescence: there are white salt deposits or efflorescence on the walls
- Water ingress: the walls have been affected by leaks or water ingress and there are salt deposits or efflorescence on the surface
All these cases have something in common: salts. Once walls are exposed to salts which now permanently become part of the building fabric, the replastering has to to be done with a salt-resistant plaster. This is very important. Failing to do so, by just using a "normal" plaster, the new decoration will not last very long; it will be sooner or later spoiled by the crystallizing salts and the walls will need to be redecorated again - a potentially costly and messy exercise.
Salt Resistant Plasters
There are a number of salt-resistant plasters on the marketplace. These are also called renovation plasters and they are typically used for re-plastering after rising damp treatment to prevent the re-appearance of salts. Here is what you can buy:
- Cement based renovation plasters: most of these renovation plasters are cement based. They are not breathable and to a large degree they will only conceal the problem rather than permanently fix it.
- Lime based renovation plasters: lately, some lime based renovation plasters have also appeared on the UK marketplace. However, these also contain cement and often chemical additives.
- Lime only renovation plasters: "pure" lime only renovation plasters with NO added cement are best and recommended for listed or very old buildings where salts are a problem.
Now, from practical viewpoint, taking into account the performance / cost ratio of these plasters, which one should you use?
- If you want to go for the bare-bones solution, without particularly caring about breathability or the long-term implications of the plaster onto the building fabric, a cement-based renovation plaster will most likely be your choice.
- If you want to keep the building fabric breathable, your choice is most likely be either a lime-based or lime-only renovation plaster.
- However, if you want to get everything done right, especially if the building is listed or of higher value, lime-only renovation plasters would be your best bet.
Rinzaffo - Lime-only Renovation Plaster
Lime-only renovation plasters are hard to find as they have are catering to a niche market, have a special composition, and because they do not contain cement they are manufactured by smaller family-run businesses based on old, traditional recipes.
The best plaster we have found is manufactured and imported from Italy and is called Rinzaffo. The RINZAFFO lime scratch coat has been developed in 1980 in Venice as a specialized solution to the problem of capillary rising damp, however its origins stretch back to ancient Roman times. Roman architect Vitruvius was the first one who described these plasters in his book "Ten Books of Architecture".
RINZAFFO MGN is a natural hydraulic lime mortar, made salt resistant with the addition of pozzolanic hydraulic binders, marble powder and traditional natural organic additives (e.g. fats, proteins of plant or animal origin) giving this plaster additional water repellent properties.
Due to its unique pore structure, it prevents the crystallization of salts inside its pore structure. By regulating the evaporation of humidity it keeps salts residing inside the wall capillaries in a dissolved state thus preventing rapid salts crystallization responsible in the detachment of plaster from the walls and the deterioration of masonry. As a result the surface of the plaster stays dry and healthy, and the appearance of the interior remains aesthetically pleasing.
Since its inception in 1980 this plaster has been extensively used in the Venice lagoons in very wet conditions and extreme saline aggression. After almost 40 years of service, Rinzaﬀo plasters still perform extremely well without breakdown or structural damage despite of being periodically submerged into the “high waters” of the Venetian tides. Te performance of the plaster is still being actively monitored today in order to assess its aging and to make continuous improvements to the product.