Another damp problem

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18 Nov 2014
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Location
Norfolk
Country
United Kingdom
My house is rendered on the outside from about 8" above floor lever all the way up to the roof, apparently due to Norfolk bricks being soft in the early 1900's. From what I have read this is making my problem harder to get rid of.

My problem is there is an inwards corner (if that makes sense) where the living room meets the kitchen an in the corner on the outside of the house the drain pipe comes down from the roof and into the ground. The ground is block paved. When we moved in the block paving in this corner had sunk down slightly and was causin a puddle to form in this corner when it rained. I dug up the block paving and found the drain was also broken just here causing all the ground under the drive in that corner to be absolutely saturated from years of water leaking into that area. It was like clay! Anyway, new drain in and block paving laid tilting slightly seat from the house = no more puddle in the corner. Now to inside...the living room had clearly been suffering from damp in the wall in that corner, the house had been damp coursed twice in the last 15 years and also had waterproof plaster up to halfway up the room. So what is happening now is we are getting a damp patch halfway up the wall about 1.5m long. We had a dehumidifier in the room for ages, and a electric heater for days, the wall dried right out, I painted it and it went away but then over a few months it slowly comes back.

I'm guessing the render is stopping the wall from drying out, my builder has suggested stripping the plaster off the inside and leaving it of for 6 months and before replastering....is this the only way? I don't really want to have such a mess in the living room for 6 months for something that may not even work.
 
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Hi, thanks for the reply. I have read this before about damaged rendering sucking in water and have inspected my rendering closely and there is no damage at all to the outside. It is cement render but has been on the house for around about 100 years, I think the problem was the damaged drain that was left I repaired for years, combined with the waterproof plaster inside the house the only place for the water to escape and evaporate is just above thee waterproof plaster level which is where the damp is. I think the cause of the problem is solved, but the wall is saturated and has been for many years and sealed in on one side by render and he other side by waterproof plaster. Don't you agree this could be the damp cause now? Is the only way to remedy it completely to remove either the render or the plaster to let it dry out?
 
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"The wall is saturated" I'd check this out. Your bricks below the DPC on the outside are probably saturated due to groundwater. You can often check this by drilling into a brick and into a mortar bed at ground level, and the drill bit flutes should be filled with a clay-like sludge, and steam as you pull the bit out.

Now if you drill into your wall through the render, and on the inside wall through the damp plaster, and the result is not the same - i.e. dust comes out with the drill, and not sludge, your wall is far from saturated.

That's not to say that there is no dampness in the wall, but you should find the dust a hopeful sign. It is possible that only the plaster is harbouring condensed water in contact with a generally cold wall. It is possible that the "waterproof" plaster has different thermal properties to the rest of the older plaster, demarking the boundary between them with an obvious damp line

One way to accelerate the drying process in a damp wall, from the inside, is to use an ordinary unheated fan to maintain moving air over the damp patches. It may be more convenient to use the fan overnight, avoiding draughts and any fan noise when the room is occupied. The draught will initially enhance evaporation and discourage condensation, but later will warm the wall to the same temperature as the air in the rest of the room. At the very least, it is a no mess solution.

Fans are much lower in energy costs than using dehumidifiers, which I believe are useless in occupied rooms, and are only really effective in closed off spaces, which are not exchanging air with other spaces and the external air.
 

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