Hi, My kitchen sink waste water pipe leaves the building through a gap in the inner cavity wall (see picture). I want to fill it, as we've had some external drainage problems and there is a bad smell that builds up in the cavity, and can fill up the kitchen and other rooms. Problem is I'm not sure the best material and technique to use. With nothing behind the gap I want to fill apart from the cavity itsself, there's nothing for concrete to hold on to .. and I'm worried its just going to collapse as I'm applying it.
Any advice on this gratefully recieved.... Andrew.