Damp walls; are Rentokil the only way?

[Ellen Rawlinson]

I have just bought a very wet house! Semi detached about 100 years old. I've taken some steps to try and cure what I thought the cause of the problem was i.e. removing the 12 inches of concrete that encased the building above the internal floor levels, fixing drains, removing

3 feet of concrete render along one side, gutters etc. It subjectively feels much drier even after only 4 weeks.

Knocking off the damp plaster throughout to about 1 to 1.3m reveals that the bricks have been injected at some point in the past. I wasn't sure what else needed done, so Rentokil sent along a surveyor today to have a look. He drilled a hole in a wall, put the dust in a flask type thing and showed me that it was 10% (apparently 4% or above is a problem).

He's suggested 2 things;

1. Injecting the mortar just above floor level throughout, cost £1200 (exc VAT)
2. Getting Rentokil to plaster as well, with 'special' plaster that will repel the water still in the damp bricks, cost about £3000 (exc. VAT)

He says that if I put normal plaster on the walls without letting them dry out, the new plaster will crack and fall off. A little research suggests two alternatives to rather expensive Rentokil plastering;

1. Cover walls with PVA and then apply plaster with 'waterproofing' mixed in (what is this waterproofing bit?)
2. Cover walls with cement render, which I'm told is waterproof, with added benefit of adding support to slightly dodgy brickwork.

Does anyone have any advice for me on these points? It is probably clear that my building knowledge is limited, so please assume I know very little if you reply!! Whilst the house is a building site it would be great to get this all sorted, and not have to worry about it in the future.

Thanks in advance for any assistance, Ellen

[Richard Faulkner]

In message , Ellen Rawlinson writes

Get comparable reports and quotes from 2 or 3 members of the BWPDA

are a big brand name and almost certainly charge accordingly.

[Rick Dipper]

My architect has a big problem with these injection solutions, He says it takes 10 years for the damp to rise 1m in a wall, so if you hack off 1m of plaster, and replace with waterproof plaster, you need do noting else, to achieive a 10 year solution.

There are tanking membrans that you can fit under plaster, I will fit these to the walls in my house that have no DPC.

Cement render really needs a waterproofer, its only waterproof if its made really strong, and then it srinks as it sets ..... There are many available.

There are some electronic systems, I looked into one, but when I told the sales guy building regs wanted to see the BBA cert for it, he ran a mile.

I suspect you need a guy who knows his stuff to vist your place, rather than a guy trained for 3 days in a classroom.

Rick

[Christian McArdle]

Let the walls dry out naturally. You've probably already fixed the problem and don't need to spend thousands on solutions that may not be necessary.

If you can't wait to plaster, consider using a lime plaster, which will breathe naturally. In the meantime, keep the property well heated and consider buying/renting a dehumdifier to speed up the process.

Alternatively, if the internals of the house have no particular historic significance, such as original cornicing or plaster detailing, then consider drylining instead of wet plastering, using celotex/kingspan. This will dramatically increase the comfort and energy efficiency of the house and none of the damp will get past the insulant and vapour barrier to ruin the attached plasterboard/paper. Even 10mm of insulation would make a significant difference, whilst 25mm would be good and 50mm excellent. If you've knocked off the bonding plaster, than a 25mm total thickness of insulation and plasterboard isn't that much thicker than wet plastering.

Christian.

[Andy Dingley]

Congratulations. Now the sensible thing to do is ignore the problem until next Summer. We've had a wet Autumn and it's going to get worse. Assuming that your guess is exactly right (and I bet it was), then your house will remain damp for quite some time - nothing short of freeze-drying it is going to remove the existing moisture, so you're just going to have to wait a while to really find out what's what.

No-one with a shiny suit and a magic meter knows _anything_ more than this. You know the walls _were_ wet, you now have to hope you've removed the single cause and that drying out will improve things. "Tests" won't tell you any more about causes than simple visual inspection.

In the meantime, assume the worst. Don't hang valuable pictures on outside walls. Put some $5 hygrometers around the place. Think about a dehumidifier. Don't redecorate yet, and expect to do so next year.

That's even more than I would have done so far.

Never mind. I'm sure there's a pest control company that can eradicate it. Just keep the food in sealed tins and don't let them build a nest.

Rentokil are not a trustworthy company for damp proofing (Look what happened over their past guarantees). "Surveyors" that work for solution companies are implicitly untrustworthy. You've very probably fixed the real problem of the exterior bridging and internal injections et al. are a very poor second best in comparison.

BTW - What happened about the original buyer's surey and spotting the bridging in the first place ?

[Anna Kettle]

Sounds good. Sit tight until after next summer to give everything a good chance to dry out, but I can imagine you don't want rough brick walls for that long so ...

I wouldn't use anything waterproof. Waterproof means that water can't get through it, but the water doesn't magically vanish, it just goes somewhere else which can easily be into the plaster which is a couple of meters up your wall so you are just moving the problem elsewhere

I'd plaster with lime plaster instead of sand&cement render or gypsum plaster. In a 100 year old house your original plaster will be lime plaster - it only went out of fashion after the last war. Lime plaster doesn't fail when it gets wet, in fact it is breatheable (which neither sand/cement render or gypsum are) which means that gradually moisture will escape through it. If you use lime plaster then don't paint your walls with modern plastic paints or use vinyl wallpaper which will trap the moisture again - at least not until everything has dried out well

The problem you are likely to have is finding a plasterer who is willing to use lime plaster (they don't get taught that in college these days) so you might end up DIYing it :) You can try asking your local council conservation department for names of lime plasterers

Shout if you want any more advice

Anna

~~ Anna Kettle, Suffolk, England |""""| ~ Lime plaster repairs / ^^ \ // Freehand modelling in lime: overmantels, pargeting etc |____|

01359 230642

[N. Thornton]

ugh, youre barking right up the wrong tree. Dont even go there. The experts are here, you need to understand the important concepts:

do whats youre suggesting.

NT

[Grunff]

Pointless (for you, at any rate)

1. Fix whatever drainage exists around the outside.
2. Adequately ventilate.
3. Adequately heat.
4. Replaster.

Our 1930s house has no dpc and no dpm. It was very damp when we moved in

3 years ago. Very, very damp. Following the above steps (all advice from this group BTW) has completely removed the damp.

[stuart noble]

Having dealt with half a dozen similar problems over the years, I would say the simple solution is to use a pva modified mortar to bond Aquapanels to the inside brickwork. If the outside is being painted, use a solvent based pliolite masonry paint, which is genuinely water resistant but still gives a matt finish. As to walls breathing, lime mortar, and other mud hut technology, I'd say that nothing stops the passage of air through mortar. Okay, walls have to breathe, but you need to stop them drinking.

[N. Thornton]

I dont think theres even any such a thing :)

[Roger Moss]

I like the idea of lime - but is it strong enough to put screws in? I have memories of old houses with light fittings, bannisters etc dangling where rawlplugs have turned what should have been a nice 6mm hole into a dusty, almost conical excavation.

Is there some special technique for fixing shelves, heavy mirrors etc to a lime plastered wall (without drilling through in the hope of finding a lump of stone and using 6" frame fixings to reach it!)?

Around here it it so difficult to get anyone who says they will come and plaster to actually come and do "your" job that one daren't frighten them off with talk of lime...

Roger Moss

[Ellen Rawlinson]

"stuart noble" that nothing stops the passage of air through mortar. Okay, walls have to

Thank you very much for the advice. At the risk of looking a fool, could I ask what aquapanels are?!

Ellen

[Ellen Rawlinson]

I bought it knowing full well it was very damp. I got a full structural survey from a very helpful, friendly and talkative surveyor, and this, along with detailed inspection, suggested doing the things I've already done would go at least part way to solving the problem. I just wasn't sure if I still needed things like injections or mechanical DPC etc as well.... unfortunately getting Rentokil out didn't really help!!!

[Dave Plowman (News)]

Both these treatments used to be a near essential when obtaining a mortgage some years ago on any similar aged house. Like mine. As part of a damp/woodwork warranty that the BS insisted on. And the first few companies I tried insisted mine needed it (using their measuring instruments) and it was the only way.

But the house has beautiful high Victorian skirting boards, and I didn't want to lose them.

Eventually, I found a company which would fix the wood rot - there was some - and supply the required warranty. Without installing either a 'damp course' or re-plastering.

30 or so years on, I dunno if I have damp or not. Nothing goes mouldy, and wallpaper stays on the walls. Of course the house is now well heated and ventilated.

[Dave Plowman (News)]

In article , stuart noble that nothing stops the passage of air through mortar.

If you mean lime mortar, that's the reason for using it. If you mean mortar in general, surely waterproof ones are available?

Perhaps it didn't rain 100 years ago?

[Andy Dingley]

The same things I asked about just a couple of days ago. 8-)

They're a bit like MDF, except made with cement instead of woodglue. So you have a very heavy, dark grey piece of "board" that doesn't mind getting wet. Popular for making shower enclosures, because you can tile over the top.

A few years back I made a Gaudi-like tiled garden pond from this stuff

- Aquapanel, bought from Wickes. This week I'm replacing exterior fascia boards with another brand, Viroc Versapanel. Following recommendations though, I'm having the plywood shop saw it to size for me, to save dust and wear on my tools.

I also have a suspicion that 20 years ago this stuff was radically new, and I bought a pair of hand-made speaker enclosures made from it. "Musician Bonsais", individually made drive units by a lab technician (?) at Liverpool University. And very good they still are ! It's an excellent material for making speakers - even better than MDF.

[Andy Dingley]

It's just timber and some time on the spindle moulder. You can have them any made shape or size you want, and it'll still be cheaper than B&Q,

[Dave Plowman (News)]

Was even cheaper not to have the rooms re-plastered.

[G&M]

I don't really think gypsum is strong enough to support these things either.

[Owain]

"Ellen Rawlinson" wrote | Rentokil sent along a surveyor today

That is a *salesman* not a surveyor.

| to have a look. He drilled a hole in a wall, put the dust in | a flask type thing and showed me that it was 10% (apparently 4% | or above is a problem).

Nah, it's only a problem if it feels squelchy when you prod it.

Others have outlined the solution.

Owain