DPC and General damp in a Party Wall

[Frazer G]

I have two linked issues so I hope this thread is started in the most relevant topic area.

 

I have a terraced house built approximately 1890 which has evidence of damp in the Party Walls (it is mid terrace). There is also some damp present in non-Party Wall areas but they are not relevant to this thread. The damp is not horrendous and appears to be restricted to about 400mm upwards with evidence of salts causing "blistering" of the paint finish. I have had the property "surveyed" by a reputable damp specialist who has quoted to remove plaster to 1.2m, insert a chemical DPC, fit damp proof membrane and re-plaster. Apart from the price it all sounds reasonable until the second part of my problem arises. Both neighbours, who I am legally required to tell about the proposed works, are being difficult. They are both suggesting that their properties do not have a problem and if I put a DPC into the wall it may upset the "balance" and give them a problem. The contractor I have a quote from says that such a thing is extremely unlikely (note he has not given a guarantee that it will not happen and he will only warrant work he does to my side which is understandable).

 

A part of my thinking is actually wondering if the neighbours have done something to prevent the appearance of damp on their side which has in fact driven the damp my way! They will not have inserted a DPC or they would not be worried about me doing so.

 

The act specifically gives property owners the right to insert DPC's into Party Walls but only after a surveyor gives an adjudication in my favour. As there are two neighbours, if both push it to the limit I could be spending over £2000. I am not in the camp of those who may advocate the old mantra "Publish and be damned!" so I want a solution which will not come back to bite me later.

 

Which brings me back to the damp "cure" and a suggestion which, before you all shout at me, is not an ideal solution. Much of the plaster in the affected areas is old and in some areas only held in place by the paint and wall paper! There is nothing to stop me removing this damaged plaster (it is my judgement what is damaged!) as in normal decorating procedures, omitting the insertion of a DPC (which would save me money!) and applying tanking screed. The fixing of a membrane and plastering to blend in with the rest of the wall would be as quoted. As an alternative I could omit the tanking screed which would have greater potential to trap the moisture in the wall. Under this proposal I doubt I would get any warranty from the contractor.

 

Given my dilemma comments and suggestions will be most welcome. The matter must be resolved as I have been told that with the current evidence of damp a buyer would be unlikely to be able to secure a mortgage.

[joe90]

On a previous semi detached house I had for a short time damp appeared in the party wall and I traced the cause to a blocked rainwater drain which was actually the neighbours but on the boundary. I cleared the drain, removed said plaster, let it dry for a few weeks, replaced plaster and no more problems. See if you identify the cause (drains, soil above DPC etc.)

[Frazer G]

Thanks joe90. Unfortunately life is not that simple for me as the problem is along a two walls both about 4m and separated by about a 2m gap. Pretty much no what the problem is, penetrating and rising, so no easy solution.

[joe90]

3 hours ago, Frazer G said:

penetrating and rising,

Well no, penetrating can’t occur on a party wall as both sides are “indoors “ but rising is obvious.

[Marvin]

2 hours ago, joe90 said:

Well no, penetrating can’t occur on a party wall as both sides are “indoors “ but rising is obvious.

I assume there is no chimneys on the party wall.....

[Roger440]

Rather depends on how "bad" the damp is.

 

Id be tempted to remove plaster and allow to dry out. If it does, ie, its dispering happily into the room, then simply replaster with lime plaster. (and lime paint)

 

Sometimes the simple solutions are best. Worked for me.

[Mike]

1 hour ago, Roger440 said:

Id be tempted to remove plaster and allow to dry out. If it does, ie, its dispering happily into the room, then simply replaster with lime plaster. (and lime paint)

I agree. Also make sure that you have adequate ventilation in the room.

 

12 hours ago, Frazer G said:

wondering if the neighbours have done something to prevent the appearance of damp on their side which has in fact driven the damp my way!

I suspect that it could be the other way round - that your side may have been replastered at some point with sand-cement and/or gypsum, which can be problematic on traditionally built houses.

 

[Frazer G]

Thanks for all the replies. In my case joe90, because there is a height difference between the two properties and mine is the lower one it can be penetrating damp (probably is) coupled with rising damp. Since posting I have discovered that the walls are actually cob built with random stone up to 20" thick so a conventional chemical dpc will not work anyway. Current thinking is to remove the plaster and apply a tanking solution, followed by a damp proof membrane and the render. An alternative I am considering is to apply plasterboard to the treated areas using dot & dab (I am assured it will be 100% OK with a membrane in place). That will save me the cost of plastering as the PB will only need a skim to blend in with the remaining unaffected surface. Another plus is as I am not drilling holes in the wall for the DPC my work doesn't fall into a category where the Party Wall act applies.

Comments based on this revised situation will still be much appreciated.

[Mike]

5 minutes ago, Frazer G said:

Current thinking is to remove the plaster and apply a tanking solution, followed by a damp proof membrane and the render.

Not a good idea, for two linked reasons:

1. It should stop the moisture appearing where it is now, but due to capillary action within the wall it's very likely to emerge higher up (or to your neighbour's side, if you tank high enough).
2. The build-up of moisture in a cob wall can cause it to deteriorate, potentially to the point of collapse.

Instead, use materials that allow the moisture to escape.

On 29/09/2024 at 21:26, Roger440 said:

Id be tempted to remove plaster and allow to dry out. If it does, ie, its dispersing happily into the room, then simply replaster with lime plaster. (and lime paint)

This remains your best course of action.

[Roger440]

5 hours ago, Frazer G said:

Thanks for all the replies. In my case joe90, because there is a height difference between the two properties and mine is the lower one it can be penetrating damp (probably is) coupled with rising damp. Since posting I have discovered that the walls are actually cob built with random stone up to 20" thick so a conventional chemical dpc will not work anyway. Current thinking is to remove the plaster and apply a tanking solution, followed by a damp proof membrane and the render. An alternative I am considering is to apply plasterboard to the treated areas using dot & dab (I am assured it will be 100% OK with a membrane in place). That will save me the cost of plastering as the PB will only need a skim to blend in with the remaining unaffected surface. Another plus is as I am not drilling holes in the wall for the DPC my work doesn't fall into a category where the Party Wall act applies.

Comments based on this revised situation will still be much appreciated.

 

This is disaster looking for somwhere to happen. Probably in your living room.

 

Cob walls really, really dont like being wet. Plenty in devon and cornwall that have collapsed for this reason.

 

If you do any of the things you have suggested, where do you think the moisture will go?

 

Or put another way, if you washed your clothes, took them out of the washing machine, put them in a plastic back and hung it on the washing line, what do you think will happen?

 

Ill give you the answer. They will stay wet.

 

This is exactly what you are proposing to do, with the inevitable outcome.

 

I gave you your only viable solution. It remains the only sensible one, especially with a cob wall.

[Frazer G]

Replying to Roger440- thanks for your reply. If this were a Cornish country cottage (or Welsh) that is exactly what I would do and actually did to my daughters cottage in Wales. People looking to buy such a property in such locations expect that kind of finish. However in more urban places such finishes are not so popular. I 100% agree with the analysis  of wet washing etc and the need to avoid trapping the moisture hence my search for a solution which achieves an acceptable finish which will have a reasonable life span. I should say the damp is exactly that, it is not running water, so should be containable. 

 

The "go to" renders are apparently applied to membranes which have a textured internal surface which allows to air to circulate behind the render but my logic is that unless the membrane is open at the top and bottom the air will not actually circulate. The open bottom is easily hidden behind a skirting board but keeping the top edge open with an aesthetically pleasing appearance is more difficult. My own home is stone built and butts into a hillside. Here about 30 years ago I used battens and foil backed plasterboard with insulation between the battens. There is no trace of damp on that wall. 

 

I could do exactly the same thing in the property in question but the geometry in the current setting is not so friendly so the "membrane solution" would be easier IF IT WILL WORK or if there is a more modern solution (my solution was OK 30 years ago) where experience is held by forum members. Hence my questions.

[Mike]

9 hours ago, Frazer G said:

However in more urban places such finishes are not so popular

No need to worry about urban popularity. Once painted, most people wouldn't easily see the difference, if the plastering is done well. You won't get the glass-smooth finish of gypsum, but lime can still be finished smooth. Clay-based paint is a more durable alternative to lime-based, proving a good quality matt surface, and I'll be using it here on my current project in very urban France, alongside the linseed oil paint on the windows.

 

So no need to worry about urban popularity. I'd be much more concerned about the structural stability of the wall. Stick to the way it's been done for centuries, rather than looking for questionable high-tech solutions.