Our lower ground floor flat (built early 1970's) is slab and screed. We pulled up the 70mm screed (in which water, radiator, electrics, phone and television were all routed in pipes) in half (40sqm, one large L shaped room) as part of a gut and refurb (moving kitchen, redoing plumbing, rewire, etc) - we're installing wet UFH (20mm of kingspan, then UFH and 60mm of screed).
I found that between the slab and screed is a layer of bitumen - this is the damp proofing - well, due to years of occasional grey water leaking from a downpipe in one corner, it looks like the bitumen had eroded in parts - some of the steel pipes for the electrics were substantially corroded. This might explain why the underlay from the carpet we ripped up was damp (yuck). We'll fix the downpipe (ABS grey water into a steel pipe, without a, or long gone. seal). There is DPC around the walls (breeze blocks) but it is not always protruding far enough (in a few places, can't see it at all). Also there is no DPC around the pylons (holding the building up
). It looks like the bitumen goes under the DPC (either after the walls were built or before, anyone?)
What's the best way to put the damp proofing back in? It seems either to fully put bitumen back in, but this would mean to strip back all of the existing bitumen - not the easiest task because the slab is not smooth, has quite a lot of ribs in it. I thought to use cromaprufe around all the edges (in generous amounts) to reseal the DPC at the walls, with a ~10-15cm border on the slab, then to use DPM and join the DPM to the bitumen border (the DPM can run over some of the old bitumen and I can use some sand to fill in some of the gaps, etc) - is thus possible (e.g. how do I fix the DPM to the cromaprufe, or do I just lap some of it over the DPM)? Advice much appreciated!
Also, does it matter about the parts where the DPC is not protruding from the brickwork?
(I am doing the insulation and UFH pipes, then we are getting a pro to screed the floor - don't trust myself on that!)
I found that between the slab and screed is a layer of bitumen - this is the damp proofing - well, due to years of occasional grey water leaking from a downpipe in one corner, it looks like the bitumen had eroded in parts - some of the steel pipes for the electrics were substantially corroded. This might explain why the underlay from the carpet we ripped up was damp (yuck). We'll fix the downpipe (ABS grey water into a steel pipe, without a, or long gone. seal). There is DPC around the walls (breeze blocks) but it is not always protruding far enough (in a few places, can't see it at all). Also there is no DPC around the pylons (holding the building up
). It looks like the bitumen goes under the DPC (either after the walls were built or before, anyone?)What's the best way to put the damp proofing back in? It seems either to fully put bitumen back in, but this would mean to strip back all of the existing bitumen - not the easiest task because the slab is not smooth, has quite a lot of ribs in it. I thought to use cromaprufe around all the edges (in generous amounts) to reseal the DPC at the walls, with a ~10-15cm border on the slab, then to use DPM and join the DPM to the bitumen border (the DPM can run over some of the old bitumen and I can use some sand to fill in some of the gaps, etc) - is thus possible (e.g. how do I fix the DPM to the cromaprufe, or do I just lap some of it over the DPM)? Advice much appreciated!
Also, does it matter about the parts where the DPC is not protruding from the brickwork?
(I am doing the insulation and UFH pipes, then we are getting a pro to screed the floor - don't trust myself on that!)
