Hudson Lambert, director of Safeguard Europe, looks at the alternatives to traditional plasters
Gypsum-based plaster systems are lightweight, cost-effective, and easy to apply. However, they suffer from the major disadvantage of being highly susceptible to moisture. Gypsum plasters are very porous and will draw through any moisture from the underlying wall – resulting in visible damp patches. Over time the moisture can dissolve the gypsum, leading to crumbling. Where the moisture contains salts (e.g. from rising damp or chimney damp) the damage can be more pronounced as these can react with the gypsum, causing it to “blow.”
For this reason, alternative damp-resistant plaster systems should be considered whenever renovating existing properties – especially those of solid wall construction which can be particularly prone to water ingress. During a typical refurbishment project attempts will usually be made to deal with any underlying damp issues – for example, the installation of damp-proofing rods, external repointing, crack repair, masonry water repellent creams, etc.
However, it can be very difficult to cover all bases. Successfully identifying and dealing with all possible paths of water ingress can be a near impossibility, especially when the possibility of future defects and maintenance issues are considered. Choosing to use a damp-resistant plaster system, rather than a standard gypsum plaster, can therefore provide a valuable second line of defence against any unexpected moisture ingress.
The best damp-resistant plasters offer similar physical characteristics to lime plaster, in terms of hardness and breathability, but offer enhanced resistance to moisture and salts. Such plasters will normally be CE-marked as ‘Renovation Mortars’ under the EN998-1(R) standard – not to be confused with general-purpose plasters that carry the EN998-1 designation, but without the all-important ‘R’ suffix.
Although these plasters typically incorporate cement as the main binder component, a high proportion of lime can often be incorporated into the mix – as in the case of our own Dryzone Hi-Lime Renovation Plaster.
Hybrid plasterboard systems
These allow the use of standard gypsum plasterboards over walls that may be susceptible to moisture ingress. A silane-based cream is applied to the wall surface prior to the fixing of the plasterboard. This acts to reduce water ingress and salt formation. It also acts as a primer for the water-proof silane-modified polymer adhesive that is used to fix the plasterboard in place of the traditional gypsum bonding adhesive. These systems have the advantage of being extremely fast to install.
These are designed to allow the use of a standard gypsum plaster on a wall that might be prone to water ingress. This is achieved by forming a physical barrier between the underlying wall and the plaster layer.
In recent years meshed “plaster membranes” such as Oldroyd Xp have become popular for this purpose. However, they suffer from the disadvantage that a high number of fixings are required per m2. These all must be fixed into an 8mm drill hole which can mean that hand-arm vibration issues can limit the amount of membrane that can be fixed per day on larger jobs.
A more recent development is DryBase Flex membrane. This is a plastic membrane with a polymer felt on each side. It is simply fixed to the wall using DryBase Flex Adhesive. A standard gypsum plaster can then be applied directly onto the membrane.
Barrier systems need to be used carefully, as by their very nature they are non-breathable. However, there are certain circumstances in which they can be very useful. For example, their ability to block salts and tars makes them a very attractive choice when plastering over old chimney breasts.
For further information on Safeguard Europe visit safeguardeurope.com