Salt migration to wall surface causing damp

[Fergus McMenemie]

I have an house constructed from old farm buildings. We have persistant damp problems in one or two areas of the house. Its generally a plastered wall, we have had back the guy who did the damp proofing a few times. He tested the wall and stated the wall got damper higher up. We called in the roofer who found nothing.

I than ran into somebody who said it was salt within the wall migrating to the surface of the wall. The salt was such that it attracted mosture out of the air causing the damp patches. Internally the wall is day, its only the surfaec that is damp.

Has anybody else run into this?

Also; what do I do about it? I was told to strip the plaster and replaster with some special kind of plaster that blocks the salt migration. What kind of plaster do I need to use? How well does it work?

I have been given quite a bit of duff advice from "experts" over the years, so I want to hear what the group thinks.

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RT

[Lobster]

Do bear in mind that it's a fact of life that no damp-proofing contractor will ever, ever tell you that a recurrent damp problem is due to problems with the work they did and that in the entire history of mankind, no DPC guarantee has ever been honoured (Clarkson mode off)

David

[Newshound]

Snap. There are people who say there is no such thing as rising damp. Where I live (old limestone house, built straight on the limestone, at the bottom of a hill) I sometimes think if I set a tap into the wall, I could use it as a spring.

[The Natural Philosopher]

Indeed. Rising damp is a total fact. but in general it gets dealt with one way or teh other or the house doesn';t last.

BTW the salts don't cause the damp, the damp causes the salts...(to migrate)

Dlast hih up a wall indicates either high level damp getting in, or low level damp that has had to go that far up to get out...due to waterproofing on the wall surface below.

[Mark]

Well ignoring the varied views on damp remedies

but to answer your question. All the wall plaster should be removed back to brick, the walls should then be treated with a salt inhibitor (acetic acid), the walls should then have one coat of plaster at 3 sand 1 cement with the appropriate water proofing add-mixture when this has set but is *still green*(Important ) another coat of plaster at 5-1 sand cement mixed with clean water should be applied. After this has dried completely you can the finish with ordinary gypsum plaster.

Well it does work, but when if does fail it's a bar-steward to fix the second time around.

-- Mark§

[Stuart Noble]

"> Well ignoring the varied views on damp remedies

Or use aquapanels. More expensive in materials but, if it's a smallish area and/or your plastering skills aren't up to much, and/or you don't want to wait for it to set, then they're a viable option. Pretty easy to bond to the brickwork with sand/cement/pva and maybe a couple of screws per board.

[Lionel]

Barn conversions are notoriously difficult to treat for rising damp. They are often made of difficult materials - e.g. earth-retaining walls, or even mud. Furthermore, there tends to be a high concentration of salts (caused by many years of animals urinating, I'm afraid to say!). For this reason, special plaster membranes are now commonly used to cover up the damp rather than actually stop it rising up the wall (for an example, see

). A further advantage of this type of solution is that it is easier to reverse than putting a hard render on the wall, making it easier to meet the requirements of listed buildings officers.