damp in annexe, advice needed

[andynewton]

The annexe has been built with part of it attached to the main house. At this part the damp is showing on the plaster in the annexe (this is palster on the exterior house brick). I have cut away all the damp plaster and am able to scrape away down the side of the concrete floor, level with where the damp course is visible on the house brickwork. I have removed all the damp plaster and there is only remnants of any original damp course used in the annexe. I now have a gap between the concrete floor of the annexe and the brickwork of the house. What I amstruggling to find out is if there is a product out there that I can put into this gap as a damp course, the gap is about 10 cm wide about 5m long. The if this is filled would I be okay to plaster above it. Any help is appreciated

[welsh brickie]

I am unsure of your discribtion of the problem,A picture would be better.
10cm gap by 5 mteres? you say is a very big gap, you could lay new damp course and lay a 100mm or 10cm block on its side to fill the gap

[andynewton]

sorry, mistype, should have gone to bed earlier. The gap is about 10mm between concrete floor of annexe and brick wall of house. The concrete floor is a couple of cms above the damp course level of the house. So I am trying to find out if there are any sprays/chemicals I can put down the gap or whether I should just leave an air gap. Thanks

p.s The 5m measurement is about the length the house is in contact with the annexe

[welsh brickie]

ok ,10mm if your plastering over it use expanding foam to fill the gap its waterproof and will expand to fill the gap.

[andynewton]

Thanks for that, a lot simpler than all the horrors I was imagining.