How to deal with a bit of rising damp?

[Jimk]

Whats the floor construction?

Can you get under it? Cellar, void, whatever?

[nothanks]

A cavity wall has a "tide mark" about 200mm above the floor. The wall was originally an external wall but, as a result of building an extension, is now an internal wall. The wall has a 1930s DPC and the floors have modern DPMs. I assume that the old DPC has failed so am wondering what the best options are. At the moment I'm thinking of knocking-off the plaster to about 300mm, coating the wall with something and then rendering/plastering with an additive. The question is what to put on the wall: liquid DPM? bitumen? cement board (hardiebacker)? foil-backed plasterboard? What does the team think?

[nothanks]

Concrete, with insulation and DPM. The wall is on the original footings.

[newshound]

Brick, presumably? Not too thick? Not cavity?

I think I would be inclined to be drilling and injecting silicone to provide a full thickness barrier.

There is a risk of moisture rising higher if you seal off a lower band, depending on local hydrogeology.

What I do (random stone rubble filled walls at the bottom of a wet hill) is have the whole (limestone) wall exposed, with ventilated tongue and groove wainscotting up to about a metre. This lets the wall dry out and although I still get traces of salts above it, they are easily brushed off every year or so. Prior to that, classic damp proof treatment (electro osmotic with impervious plaster) resulted in the whole wall getting saturated up to at least 1.5 metres.

[GB]

Is that a DIY job?

Given solid concrete floors, how do you drill down low enough into the wall?

[tabbypurr]

Rising damp does exist but is rare. It is very unlikely that this is what's going on. DPCs are therefore not often useful. You propose DPC failure - how exactly does a hard material such as slate entombed in lime or cement fail?

Bottom of interior wall damp is usually from condensation. A wet slab from a plumbing leak can also cause it.

Coating with impermeables normally results in the coated area not drying out, and the matter therefore worsening. I'd look at the slab if practical, and look to see if ambient RH in the area can be reduced. Other options are to scrape & paint the area with lime, which permits it to dry better than emulsion, and use of a dehumidifier. The last 2 are often sufficient to keep things in check.

NT

[harry]

You can hire the equipment and chemical from tool hire shop. Two holes per brick and bang plenty in.

If it's a cavity wall, the cavity may be full of cement/rubble etc. You need to make a hole big enough to get your hand in and have a look with a light and mirror. If it's full of crap you will have to rake it all out. The cavity should go well below the floor. (The crap may be bridging the damp course.)

[Fredxx]

Not many here will see your post. This is a pleasant change from your normally bigoted posts with no relevance to DIY

[Brian Gaff (Sofa 2]

Ah, that old sponge effect. Yuck.

Brian

[ARW]

Give it 24 hours and his medication will have worn off and he will be back to his old self.

[GB]

Harry usually makes really helpful posts when it comes to DIY stuff. He has a wealth of experience, and I have learned a lot from him. I just filter out the racist stuff.

[newshound]

+1, although in this case he was discussing cavity walls and it is unclear whether this is the case for the OP.

He also posts links properly labelled OT to random but often interesting photos.

[newshound]

True, but if you have it it can be dramatic

by cracking

I'd say sometimes rather than usually. And you need plumbing there for plumbing to leak

Completely with you on not trying to hide with impermeables (but OK to create new "DPC" with silicone, if you have suitable materials and construction. You can pour in an awful lot of fluid into a stone wall).

[Andrew]

The 1976-built house that I bought in 1991 had had a leaking 28 mm connection to the baxi bermuda back boiler since new, judging by the stalagmites (-tites) of crud down the side of the heat exchanger.

Surveyor apologetic but said he couldn't get the access panel off because of furniture, but added that he had noted unusually high damp readings on his meter which was unexpected in this type of modern house. He assumed it had been the result of 'cleaning'.

Luckily BG fixed it with a new heat exchanger as part of 3* service at no cost to me (which they wouldn't do now).

The water had seeped into the slab and wicked all along the felt- lagged CH copper pipes in the slab and where they crossed over the

3/4 inch iron gas feed to the kitchen, the latter has almost corroded through.

I only discovered this in 2004 when I dug out the screed and put down 70mm celotex between battens on a 2nd dpc, plus hardwood floor.

[tabbypurr]

that's what matters

any type of damp can

A crack means 99.99% complete prevention of what is a rare condition. Not worth spending time on.

No you don't, a leak into a concrete slab can run a long way within the slab.

It's also ok to walk down the road throwing your money & time away. But I would not personally recommend it.

NT

[newshound]

Well I have seen damp regions inside a Victorian property with slate DPC where there wasn't any obvious external problem.

Yes, if you have a slab

Well the previous owner of my house cost me quite a lot of money by putting up studding over a wall with rising damp, stapling polythene over the whole area, and then plasterboarding inside. It didn't take many years for dry rot to take out the staircase, the window frames, and parts of the floor above. This is the one I cured by exposing *all* the stone inside, and adding ventilated wainscotting. If I had wanted it plastered, the only solution IMHO would have been silicone injection. I didn't do it because of the cost and the risk of gaps.

[tabbypurr]

Not unusual. Seldom does it have anything to do with rising damp, though it's often misdiagnosed as that.

As has been repeatedly established elsewhere, rising damp is rare & a highly unlikely diagnosis. The common causes of damp problems in Victorian walls are blocking ventilation & evaporation, faulty rainwater goods, condensation and plumbing leaks. Silicone injection does not address those - but it does make poeple money.

NT

[George Miles]

experts on damp are Peter Ward

also checkout Charlie at and hundreds of youtube videos selling injection solutions which only work in 1% of cases

[g]