Hi,
I have a 1960s single skin utility extension at the back of my property. The exterior walls are rough cast rendered. Below this are a couple of layers of brick with a "black line" between them (one layer above ground level). I assume the "black line" is the damp proof membrane. The brick layers were covered with a cement coating which was painted black. The cement is crumbling and falling off, so I'm wondering whether this cement needs to be replaced or if this is an outdated method.
There was some moisture on the concrete floor inside the utility adjacent to the wall during winter. As an experiment, I put a piece of roofing felt on the path outside and up the wall covering the bricks. It's been dry since, but also, we haven't had much rain!
I was thinking about waterproofing the 2 layers of brick to repel rain. Is that a good idea or would it adversely affect the existing dpm? Also, should I seal the remaining mortar, remove it, or leave it alone?
Thanks for reading; I would welcome some advice.