Black walls uncovered

[Cornishcottage_]

Hi

I started to remove cement from walls that had blown and discovered black walls. It appears to be dark grey cement under the black. Any ideas what it is and how to get off?

 

[Feltwell]

I would hazard a guess at some horrible, futile attempt to "damp proof" the wall with a tar based substance. "Damp proof", in this instance, means trap the damp within the wall and not let it come through the internal decorative finish - so treating the symptom, not the cause - still leaving a cold, wet wall with all it's ensuing problems. That little patch you show there looks like an old electrical back box that's been filled in, the cable is still present (test it before cutting it!! it could be live, it's stupid but not unknown).

As for removing the black stuff, mechanical means only I'm afraid - hammer & cold chisel.

 

[RBailey]

Yeap, Feltwell is right, looks like some sort of tanking.

Also have a look at the other side of the wall for the source of moisture (high ground levels,, leaking rain water good etc.) and try to treat that as well.

Cheers,
Richard B.