Damp Problem Strategy...

[SparkyMarky]

After removing kitchen units from my new house at the weekend I discovered a bad damp problem in the kitchen extension. The bottom foot or so of plaster along one of the walls had fallen off, and any remaining loose plaster I knocked off was damp to the touch. The kitchen extension itself is about 20 years old, but the wall with the damp problem seems to have been built up from the base of an earlier wall (probably a former coal shed or workshop attached to the back of the house, which is 1880s).

The cause of the problem seems fairly obvious - the ground level outside is slightly higher (I'd estimate 4-5")than the internal floor level. Although there is a small French type drain on the outide of the wall, it obviously isn't doing enough. Unfortunately the wall is right on my boundary and the ground outside belongs to the neighbour (forming the lovely new pathway to their back door!) Presumably this is the reason why the base of the old wall was left in place at the time - to hold back the neighbours ground.

Now the strange bit. The floor slab of the extension has been poured onto a polythene sheet as you'd expect. Whoever built the extension also installed a DPC in the wall, but as it's fitted at the junction between the old and new walls it's about 10" above the internal floor level (about 6" above the external ground level). I'm guessing the damp problem is caused by water penetrating straight through the wall from the ground outside. Higher up the DPC seems to have done it's job and prevented the damp from travelling any further up the wall.

To my (admittedly untrained) eye, the problem should be fairly easy to solve (assuming that I can't persuade the neighbour to dig up and lower his path). My plan is to chip out enough of the floor slab to expose the edge of the polythene sheet, and rake some of the mortar out of the wall to expose the edge of the DPC. If I then seal the bottom 10" of the wall between the two with a liquid DPC membrane, effectively linking the underfloor DPC to the one in the wall it should form a complete damp proof barrier. Does this sound like a sensible plan or should I be thinking along different lines?

All advice appreciated...!

 

[JerryM]

Kitchen walls are always a nightmare. even if i'm injecting i always tank them just as a precaution.

i don't know how durable the liquid DPC will be in this situation (i feel you've got +ve pressure from the ground differential). i also feel your going to a lot of hard work to get a 2nd best solution. it may be ok if you render containing waterproofer afterwards.

for me for this particular case where there are obviously mistakes in the past i would get it tanked professionally or at least get a price (it should not cost the earth to tank it and leave the tanking as the finished surface assuming units will cover).

 

[Support Site Cardiff]

i work for a specialist waterproofing supplier and we have branches all over britain. there is a product called Thoroseal or another called Vandex which are cement based slurrys and have been used on a number of damp walls. my name is Richard and you can ring me on 029 2046 5553 and i can give you our nearest branches number.