Potential Damp Problem

sys_daw · 16 Jul 2008

My house has been extended over the years by previous owners so that now three of my interior walls were originally the exterior walls. Last year I noticed that at the bottom of one of these walls the paint/plaster had started blistering. The affected area rises to no more than 2 inches above the skirting board. I have recently noticed the same problem on another of my interior walls that used to be an exterior wall.

My first thought was damp but having looked at many websites on the subject I cannot find anything that matches the same symptoms that I'm seeing. For example, rising damp appears to affect a lot more of a wall. Can anyone give me an indication of what the problem might be and how it can be fixed please?

Thanks

andy2306 · 16 Jul 2008

condensation? whats rooms on the other side and whats the temperature like in there?

davebelushi · 16 Jul 2008

Could be the plaster cold bridging. Take off the skirts to check if plaster is in contact with solid floor (if solid floor).

Could be salt. Could be a million other things!

Photos?

sys_daw · 17 Jul 2008

andy2306 said:
condensation? whats rooms on the other side and whats the temperature like in there?

Hi Andy,

On the other side of one of the walls is the kitchen which will obviously vary in temperature throughout the day. The other wall has a study on the other side which is normally a steady warm temperature.

sys_daw · 17 Jul 2008

davebelushi said:
Could be the plaster cold bridging. Take off the skirts to check if plaster is in contact with solid floor (if solid floor).

Could be salt. Could be a million other things!

Photos?

Hi Dave,

I believe that the floors are solid but will have to double check. Not sure what cold bridging is but the walls would have been plastered around 4/5 years ago and the problem only started occurring last year - not sure if that helps.

I will try and take some photos and post them here.

Thanks

sys_daw · 19 Jul 2008

davebelushi said:
Could be the plaster cold bridging. Take off the skirts to check if plaster is in contact with solid floor (if solid floor).

Could be salt. Could be a million other things!

Photos?

Hi Dave,

I've uploaded two pictures, one that shows the section of the wall that is affected and the other shows the "bubbling" of the plaster/paint work.

Untitled

sys_daw
19 Jul 2008
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Untitled

sys_daw
19 Jul 2008
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davebelushi · 20 Jul 2008

it looks like a salt problem. remove the skirts and make sure the plaster is cut back around 25mm from the solid floor. brush off the salts and repaint with a standard trade matt emulsion. you will probably need to repaint again in the future as the salts continue to migrate out of the wall.

the fact that the salt is migrating to the wall surface is an indication that the wall is going through a drying out process. after a period of time the salting should stop, if it doesn't it may be that a continuing source of moisture is the cause.

check behind the skirts 1st and take it from there.

^woody^ · 20 Jul 2008

If these walls are now interior, then cold bridging is a bit down the list of possibles.

There is distinctive yellow staining and bubbling, which would indicate moisture coming out from the wall, and therefore coming up the wall.

So best to proceed on that assumption

It may be related to [extension] work done which has made these walls interior walls - plaster in contact with floor slab, missing or faulty DPC/DPM etc

Or it may be that rain or ground water only manages to soak part way up the wall before it naturally disburses - ie if you have a extended periods of rain this will get worse.

If these exterior walls are cavity, then a blocked cavity could be bridging any DPC and causing localised dampness.

Any ground salts in the plaster will have been brought up by rising moisture - they would be a symptom not a cause. So the actual problem would be to stop the moisture first, rather than just address any salt issue

anobium · 20 Jul 2008

Woody wrote

Any ground salts in the plaster will have been brought up by rising moisture - they would be a symptom not a cause. So the actual problem would be to stop the moisture first, rather than just address any salt issue

Correct, but the salts only become visible when the wall starts to dry out.
I think thats the point Davebelushi was making, ie "crystallization"

sys_daw · 27 Aug 2008

Hi All,

I took the skirting boards off and noticed that the plaster did not go all the way to the floor, there was a gap between the plaster and the floor. So I got two surveyors in and both confirmed that it was rising damp. Great.

Options are to have the walls tanked or injected but either method will involve removing plaster and lifting carpets. Great.

As a secondary observation it was noticed that the ground level outside was higher than the floor level so I've dug out a French drain to allow the water to soak away and to prevent earth from touching the exterior walls.

Just thought I'd update the post!

noseall · 27 Aug 2008

^woody^ said:
If these exterior walls are cavity, then a blocked cavity could be bridging any DPC and causing localised dampness.

this is where my money would be staked.

peteuk · 28 Aug 2008

Hi, Sorry I can't be helpful on this.
But I posted some similar pictures previously so am interested in the outcome.
We have just had the walls replastered (in the local area) and repainted with emulsion.
Sounds like the problem may recur though.......I'll follow up if it does.

Thanks,

Pete

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Potential Damp Problem

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