We have a gully/drain at the back of our 1930s built house which takes all the waste water from the kitchen and bathroom. The patio (added by a previous owner) in which the gully sits is constantly damp as is the garden which adjoins it. The brickwork which retains the patio is starting to spall. The house itself seems unaffected (touch wood).
A couple of years ago I had someone look at the drain with an inspection camera which was inserted at the manhole half way down the garden and pushed back up under the patio to the galley trap. No cracks were evident and the operator advised re-pointing some of the brickwork above the gully. This was done but there does not seem to have been any improvement. The patio slabs are cemented in place so investigation from the top is not too easy.
The drain itself has to deal with quite a lot of water for its size and the grate which sits about one metre below the patio surface is often submerged during heavy use. Could the brickwork above the grate be absorbing water during these periods and making it damp under the patio? Or could the trap in the drain be damaged in some way? If the former, can the gully be re-lined/rendered or does it need to be completely rebuilt?
Obviously we don't really want to start any disruptive and costly investigation work if there's something else we could try first.
Hopefully the pictures will help illustrate the problem.
Thanks in advance for any suggestions.
