Here in the south of England we’ve had a wet couple of years, with the paths through my local woods steadfastly refusing to dry out even by the end of summer. The incessant rain can play havoc with the walls of older homes that were constructed when weather patterns were less extreme.
I live in an Edwardian terrace with cavity brick walls – a construction technique that can on occasion be found as far back as early Victorian properties, although only really starting to become widespread around the turn of the 20th century. Cavity construction added a degree of weatherproofing to homes not afforded by earlier 215mm thick solid walls, with the cavity acting as a barrier against water that penetrates the outer leaf of brickwork.
As with many homes of a similar vintage, my walls have been insulated in the cavity with injected mineral fibre. In general, this is an effective and appropriate solution, however there is the risk that if the fibre becomes saturated then it can lose its effectiveness, bridge damp across to the inner leaf and in the worst cases collapse under its own weight into a soggy mess at the bottom of the cavity. Installers should be assessing the risk of this happening before proceeding with injecting insulation, however things can and do still go wrong of course.
Problems can also occur with injected foam insulation as any cracks that develop can wick water across to the inner brickwork leaf, resulting in damp spots on the wall. PU beads are believed to present a lower risk of issues in this scenario as they are hydrophobic and the gaps between the beads allow the water to trickle straight down to the bottom of the cavity.
Soaked walls are not only a risk to cavity insulation, they also directly conduct heat up to twice as quickly as dry masonry – this will potentially be a much bigger issue on solid walls than on cavity constructions where the inner wall will generally be protected.
Water ingress through masonry also prevents a risk to the integrity of the construction – if the wall remains damp and freezes overnight, the surface of the brick can spall (shatter) and the mortar joints can crumble. Spalled brickwork is much less weathertight than intact brickwork, therefore there is a risk that a vicious cycle of deterioration will begin.
It is straightforward to protect a masonry wall using a masonry cream – this is clear water-repellent cream that is painted on to the masonry and helps to bead rainwater, minimising the amount of water that is absorbed and keeping the wall dry. A breathable masonry paint can achieve a similar result if you are looking to change the appearance of the wall, however it is important to keep it in good condition to maintain its weathertight integrity. In the event that spalling of the brickwork has become widespread then the application of a breathable silicone render would probably be a sensible way to mitigate the problem.
It also worth checking for other sources of water ingress around the wall, for example leaking downpipes, overflowing gutters, bridged or damaged damp-proof courses as well as hard paving that is too high in relation to the damp-proof course or too close to the wall to prevent splashback from rainfall.