Damp Patches driving me mad

13 Nov 2008
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South Glamorgan
United Kingdom
Hi there

I have an ongoing battle with damp patches on the bottom of both sides of an interior wall.

Got an independent surveyor in, who thought most likely caused by condensation due to the house being unoccupied for a long while and lack of ventilation etc. I also noticed staining at the top of the wall where the bath is (bathroom is above the wall) and there was damp underneath the bath itself due to leaky pipes. Bathroom has since been replaced etc. and no new staining has appeared.

When the old wallpaper was stripped off there was dark sticky stuff on the plaster that corresponded with the damp patches. This came off easily. Hung lining paper. All seemed well, no damp patches visible. But as soon as the lining paper was painted, damp patches came through.

Sometimes the patches dry out and fade or vanish, but they always reappear. I wondered if it would be worth trying an anti damp paint/foil wallpaper on the walls or whether these are a waste of time? Would it be best to get the old plaster hacked off and replaster with a suitable plaster?

Thanks in advance for any advice!
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Also, in case useful, house was built in 1926, cavity walls, floors on ground floor are concrete. No cavity wall insulation, there is loft insulation, but probably needs redoing as was done years ago and may not be up to modern standards?
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I think the floor is damp. Have a look under the carpet. Is there a pipe, for water supply or radiator, nearby or buried in the floor?

If there was a leak above, the floor will tale a long time to dry out.
Hi - the floor is dry as far as I can tell - the concrete floor is overlaid with parquet set into bitumen. There are no pipes under the floor - the water mains comes though at a different part of the house.
I have exactly the same problem, slightly different circumstances but it may help.

Our floors were filled with concrete after the house build. Internal walls are solid brick and I suspect there's a capillary action under the membrane which is hitting the internal wall and making the base of them damp. There look to have been several attempts to inject the base of the wall, including concrete render. Interestingly it only appears in the summer when the heating is off, so I'm going to hack off the concrete render and lime plaster, hoping that this will will encourage evaporation and keep the wall drier... we'll see.

It's my only damp wall left after a battle over the last 2 years digging holes, ventilating etc. :)
Thanks Mattice. The walls here are solid brick too. It's just so annoying as all the external walls are bone dry and that's where you'd more likely expect to see damp, isn't it?.

I took up one of the parquet blocks and had a feel around under the skirting board. There was a lot of fluff under there, (probably nearly a hundred years worth!), and it felt very slightly damp, but the floor and wall themselves didn't feel damp to the touch.

I might give the anti-condensation paints a try. And if that fails might have to try your method!

I do think the ventilation is an issue though. I work away a lot so sometimes the house is shut up for a couple of weeks at a time, and that's when the damp is worse. I have been here all week this week and had the windows open all day and I am sure the damp is drying out little by little as the dry patches in the middle of the damp patches are getting bigger.
if you are often away in summer, you might try leaving the loft hatch open. It encourages airflow, and also means you do not come home to a stifling house.

use faint pencil or chalk to draw round the damp patches, and date the outline, so you can see if they get bigger or smaller. When you have had a leak it can easily take a year for wet walls to dry out.
I've tried the paints, afraid it's a waste of time.

Along the lines of John's comment, I have some condensation patches in 'dead air' corners of the house, and I'm seriously considering trying a positive pressure ventilation system. Stick it in the loft with a couple of vents and allegedly keeps the air moving for very very small running costs. Costs around £350 for a unit, should be an easy DIY.

Here's mine if it makes you feel better, dry in the rain, damp in the sun :LOL:


My last 3ft of damp. Condensation is a breeze considering the holes I've dug :p 'cuse the pun
Worth considering air bricks if not got? Neighbour of mine had damp so bad they decorated once a year and put those in last time. Helped no end apparently.
Ha, my damp patches are bigger than your, Mattice. That's nuffin' I tell you. nuffin'.

lighty man - there are quite a few air bricks on the outside of the house - are those what you mean? Or do you mean putting them inside (if I'm being stupid even asking that, excuse me!)
What height are they? Low air bricks tend to make sure under your floor is well ventilated - to make sure no wood rots etc and is very important these are not blocked. High up ones are excellent for condensation, but do make a room chillier. If you've high up ones, are they open all the way through to your rooms or have they been filled? Filled ones do create more problems with condensation. Just a thought for your situation...
Hi Blightymam - they are all low down. I have never noticed any higher up, but maybe they are blocked off inside. Will have a look outside - thanks for the suggestion!

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