My walls are letting in water! What can I do?

Tŷ-Mawr ‌‌ posted this on 6 Apr 2016

Help! My walls are letting in water what can I do?

The external protection of a building should retain vapour permeability while providing protection from liquid water ingress.

For a wall to be functioning well a certain amount of moisture can be absorbed into the wall (generally the first few cms) this then dries back out with the sun and the wind.

If the level of protection is not adequate for the level of driving rain then water can be absorbed further into the wall.

Over several winter months with sustained wet weather and little time for drying between wetting cycles a route of moisture can be formed through the wall. As soon as it reaches a tipping point and water ingresses into the inside face any subsequent wetting will often draw water through to the inside quickly and easily. This water ingress will be exacerbated by any direct routes of entry channelling water into the wall - for example through fissures in stones, cracked mortar and junctions in a wall. When water enters a rubblestone wall (more often than not built with a core of earth or local aggregate bound in a weak mix and containing voids) then it will track through the wall from the point of entry and come out in another location.

The weather in the British Isles over the last three years has been exceptionally wet during the winter months and this has led to walls that have never had damp issues in the past to suddenly show problems. This can coincide with newly lime pointed walls as the process of re-pointing has consolidated the walls, reduced moisture breaks created by voids and therefore allowed a clearer passage of moisture to track through when conditions allow. It is not a fault of the lime or workmanship rather it is a detailing issue and these walls require more protection.

To help prevent this the level of external protection should be appropriate to the building type, its location and exposure. The most basic finish would be to simply point up the wall, followed by limewash/silicate paint, then ‘bagging’ and painting, then smooth render, scraped render and roughcast render, with the ultimate protection given by tile or slate hanging.

Clear solutions such as Surfapore C or Beecks silicone plus are hydrophobing agents which work by soaking into the background and creating a barrier at a molecular level to liquid water. They do not form a film, therefore, any holes, fissures and cracks will still be open and still be routes of entry for moisture. We advise these clear solutions may be an additional help (making sure any defects in the wall are addressed first) but should not be relied upon to be the sole defence against water ingress.

A ‘bagged’ and limewashed finish can look great and give your building the protection it needs!

Categories: FAQs