1930's terraced house with 9" solid walls. Original DPC is a layer of tar sheet. There is a bodged 1970's injection DPC immediately above it.
A plasterer recently put on bottom beading under the DPC (Yes!) and plastered accordingly. Unsurprisingly, there is now damp and lots of mould in that area.
Obviously, I will have to hack off the offending plaster, remove the bead, reposition it higher up and replaster. So far, so good, that part is solved.
Now here's the main problem.
The tar DPC actually seems to be good. However, the pointing immediately on and above it is very bad, so I think that water is entering on and above the tar, effectively using the tar as a conduit.
I need to repoint that course at least. However, I am concerned that the edges of the tar may get damaged when I rake out the old mortar, or that any small overlay of mortar (between the courses above and below the tar), may itelf provoke damp.
How to play this? Put some water repellant in the mortar? Some pointing technique of which I know nothing?
A plasterer recently put on bottom beading under the DPC (Yes!) and plastered accordingly. Unsurprisingly, there is now damp and lots of mould in that area.
Obviously, I will have to hack off the offending plaster, remove the bead, reposition it higher up and replaster. So far, so good, that part is solved.
Now here's the main problem.
The tar DPC actually seems to be good. However, the pointing immediately on and above it is very bad, so I think that water is entering on and above the tar, effectively using the tar as a conduit.
I need to repoint that course at least. However, I am concerned that the edges of the tar may get damaged when I rake out the old mortar, or that any small overlay of mortar (between the courses above and below the tar), may itelf provoke damp.
How to play this? Put some water repellant in the mortar? Some pointing technique of which I know nothing?
