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Damp Proofing Question
Lime render or sand and cement
Hi there. I have a 1890's terraced house which has had a chemical damp proof course injected twice (once in 1985 and then redone in 1997). I purchased the property and hacked off the damp plaster (which I believe was Carlite and Gypsum) back in May. I was advised by a historical building surveyor to open the chimneys up, lower the patio and ventilate the property which I have done. He also advised to put lime render back on, and I have had conflicting advice as what to do next. My walls have dried a bit, and it doesn't smell of damp (although it never did). I was advised by the historic building surveyor to not bother with chemical damp proof again as it doesn't work and to put a lime render back onto the walls to allow the bricks to breathe, but I have also been advised to put sand and cement on with a damp proofing chemical mixed in with it. The damp is on the external walls in the back dining room (where there is a concrete floor which has a plastic membrane underneath) but also on an internal wall in the living room between the hallway - the living room has a wooden floor but the hallway has a concrete floor (which is also lined with a plastic membrane). Any advice would be really appreciated? Thank you
The fact that the injected dpc works have been done twice and that the property still has damp is proof that they don't work. I totally agree with the historic building surveyor about not having this done again, he is also right on the use of lime plaster over any sand / cement combination even if it does have water proof additives. I have used this approach in my own Grade II listed medieval + Victorian farmhouse and is the best sympathetic approach to dealing with damp in old buildings. Period building structures were expected to get wet / damp from rain / ground moisture but by being able to breathe the excess water simply dried out and evaporated. The main source of your problem is the replacement concrete floor (with dpm) which has changed the original characteristics of the building.
Answered 16th Oct 2013