Safeguard Europe looks at the problems that can arise when inappropriate replastering systems are used on damp walls.
In order to reduce heating costs and meet carbon emissions targets in the UK, an extensive insulation retrofit of existing buildings needs to take place. External wall and cavity wall insulation are not suitable for many older buildings and, as such, internal wall insulation is often the best available option.
Internal wall insulation can provide a warm internal environment for property owners. Unlike cavity wall insulation, it can be installed on solid walled properties. It will also not change the appearance of the exterior of the building, something that is unavoidable with external wall insulation. Internal wall insulation can also provide a thermal benefit to interior walls.
Internal wall insulation
There are, however, some inherent disadvantages to internal wall insulation. There will be an inevitable loss of internal space due to the installation of the insulation and the new decorating surface. Mineral wool insulation systems can be more than 38mm thick. This is not just a problem because of the reduction in useable space in the room but also because electrics and pipework will have to be put back in place with new fixtures. Window reveals and doorways can also pose a problem and could be a potential location for cold bridging.
These problems can be avoided by using hybrid magnesium oxide and aerogel insulation board, such as Stormdry EP-Board. This type of insulation consists of a 3mm magnesium oxide plasterboard backed with 10mm aerogel blanket. Aerogel is a very highly insulating material that, when combined with the thinline magnesium oxide board, provides the same thermal benefit as traditional mineral wool insulation systems that are more than 2.5 times thicker. This means that it can be installed around window reveals or doorways and allows for services to be refitted on their original fixtures.
Insulation without condensation
A more serious problem presented by internal wall insulation is that of interstitial condensation, which is a form of damp that occurs when warm moist air from inside a structure condenses at the point that it meets with a drop in temperature. With internal wall insulation, the interface between the insulation and the original wall is most at risk to interstitial condensation with the resultant possibility of mould growth or wet rot. This is especially true on solid-walled properties. If the wall is already damp, the risk is greater as damp masonry is particularly heat conductive, resulting in a colder inner surface for more condensation to occur.
To minimise the risk of interstitial condensation on an internally-insulated exterior wall, it is recommended to apply a deeply penetrating and breathable weatherproofer, like Stormdry Masonry Protection Cream, to the weather-facing surface. Using a breathable weatherproofer will ensure that the moisture load from rainfall is minimised but residual dampness will be able to evaporate and exit the wall in the form of water vapour, drying the wall out. Computer analysis has also shown that the combination of Stormdry EP-Board and Stormdry Masonry Protection Cream applied to a damp solid wall can reduce heat loss by up to 60 per cent whilst negating the side effects of interstitial condensation.