I’m doing some work on my parents house, which is a 1907 sandstone build end terrace cottage, with a red brick inner (cavity) wall. Mould had appeared on several patches of the plaster of the inner gable-end and front wall. Having taken-off all the old plaster (which was the original horeshair sandy mix), I noticed the penetrating damp problem is with the wall ties. These are sandstone blocks connecting the outer wall with the inner, spaced at various intervals. You can see the ties are darker from the damp, including some of the surrounding bricks and mortar (no more than one course each side and top and bottom of the sandstone tie). It’s only a minimal amount of moisture, as when you run your finger accross the tie, there’s a small deposit of moisure on your finger tip. The rest of the wall is unaffected and is bone dry.

I want to dry line the walls with wooden battens (which I will avoid laying over the affected ties), put 25mm thick insulation boards between the battens e.g. Kingspan or Cellotex, and plasterboard with tappered boards (to tape and use jointing compound) so I can sand and paint without skimming.

I’ve had some advice stating it’s ok to just treat the wall ties with either a breathable paint-on membrane e.g. Stormdry, or just paint the effected area with tanking slurry. In addition, I’ve been advised a breathable waterproofer e.g. Stormdry, should be used to treat all the outside walls (this was done some years ago, but of course may be overdue for re-treating).

Please confirm if this is ok. My concern (having read other articles) is could this push the penetrating moisure into other areas i.e. the dry bricks and mortar?

Many thanks, Kris.

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