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Armchair

'Green' damp proofing

I'm having some damp treatment done in the near future and have been looking at various companies to carry out this work. One claims to use 'environment friendly chemicals' (surely a contradiction). Is this a load of greenwashing nonsense? There is no information on their website (www.craftpreservation.co.uk).
Gervase

What sort of walls are you thinking about having damp-proofed?
It's actually very rare for an injected dmap proofing system either to be necessary or even to work without other, additional treatments.

In fact, most injected damp-proof treatments are a complete waste of time and money, I'm afraid, and the only thing that makes them appear to work (for a time) is the waterproof plaster and render that the practitioners also insist is used before they will issue a guarantee.

What is the nature of the damp problem in your property? Is it damp penetrating the walls from outside, coming up through the floor or condensing on the walls? What are the ground levels like on the outside walls and what sort of surfaces do you have outside?
The answers to those questions may well give you a cheaper and more effective solution than an injected DPC. If you have an older property which was not built with a DPC, the sort of treatment this firm suggests could well be the worst possible solution. In that sense, I fear for the cottage pictures at the bottom of the firm's page of case histories; their treatment was wholly inappropriate and would not have been approved by the local authority conservation officers.

If you do have a situation that does warrant an injected DPC, it will need to be in the form of a gravity injected silicone cream entering the mortar bed thoroughly between two brick courses just above ground level. If your house is built of stone, cob or anything other than brick, however, don't even think of an injected DPC!

But the chemicals used are not harmful, so in that sense they're 'green'.
Armchair

Thanks for the reply Gervase.

The property (which I'm in the process of purchasing) is a mid-terraced house built c1885. The damp appears to be classic rising damp, petering out about a foot or so above the skirting boards, so I think it is probably a deterioration of the slate DPC (or the lack of a DPC in the first place). I was only able to test for damp in a handful of locations due to furniture.

I've got two different contractors looking at the property so it will be interesting to see what they recommend.
sean

They'll probably tell you that you need to hack all the plaster off up to 1m off the ground for a start. Sorry if we've got any as members, but in my experience of damp-proofing contractors I wouldn't trust their advice as far as I can spit.
kevin.vinke

A guy I used to know (sounds really believeable now Laughing ) bought a house on the understanding he put a damp proof course in.
He didn't want to pay the money for the injection system so ended up diging a trench round the foundations left it a couple of months and the surveyor came back to grudgingly admit there was no damp.
Looked a bit funny but worked. Cool
Gervase

The trench - known as a French ditch - is the most effective way of dealing with damp in older properties. The usual method is to dig it, put a perforated 100mm land drain at the bottom, put a geotex sheet over that and backfill with coarse gravel so you don't end up with a visible trench in your garden.
This cures nearly all damp problems in lower walls - where it doesn't work is if you have hydrostatic pressure under an impermeable floor slab, so damp ends up getting pushed up the walls. That's best cured with a breathable floor and a sump with an active pump.
However, if your place is 1885 and originally had a slate DPC, a chemical course may be what's needed. But do check all ground levels first. Is there any point where the slate DPC is bridged either by soil or a later applied render? Is your rainwater system sound and not bringing any water into contact with the lower walls? Do you have concrete paths next to the walls which produce an upsplash when it rains?
Fixing those could end up being a lot cheaper than a chemical DPC.
And, rest assured, they will hack all your plaster off up to a height of a metre. They do that with a chemical damp proof course so they can offer a guarantee. Have a look at the T&Cs on the web site - it states that you will need to have the treated walls replastered to qualify.
Have you had an independent surveyor look at the house?
Armchair

The damp I found was on one of the party walls so I assume it is caused by deterioration of the DPC. There was nothing externally in the way of leaking gutters etc. I'm ok with them replastering as I will be re-decorating anyway.
Barnie

Gervase wrote:
If your house is built of stone, cob or anything other than brick, however, don't even think of an injected DPC!


I can't remember what the chemical was I used on our stone walls (can dig out my records to find it if anyone wants to know) but unless the regs have changed the council wouldn't pass my building unless I provided a ten year guaranteed damp proofing, so in some circumstances it can't be avoided, however it's obviously worked well because we haven't had any rising damp since injecting the walls about 7 years ago.
Gervase

Buildng Regs are guidelines only, and most more enlightened building inspectors will negotiate towards a solution, though it does sound as if Barnie's BCO was particularly mutton-headed.

Thankfully most these days realise that chemical DPCs in stone are pointless - on their own they have no effect on damp. However, they will often insist that the walls are tanked instead to counter dampness.

On a stone or other solid-walled property without an existing DPC the best way to counter damp is to remove the cause as far as is possible (by attending to ground levels, guttering and drainage) and to use breathable plasters, pointing and renders. There are sometimes cases where more is required - such as using an impermeable solution like Vandex or Newton 500 as a technnique of last resort when faced with penetrating damp and no prospect of altering the outside soil levels.

Your average damp-proofing contractor, however, will simply stick his probes in the walls, inject the required number of litres of silicone and then replaster with a waterproof plaster. It's what they all do. And it works for a decade or so, but in time the waterproof plaster cracks or the underlying stonework spalls and the damp comes back through. Meanwhile, any timber in the wall - joist ends or lintels - will have started to rot thanks to being saturate. The long-term result is often a bigger bill for more drastic structural work and lasting damage to the fabric of the building.

That's why English Heritage and SPAB advise home-owners to think very carrefully before they do it.
Barnie

Gervase wrote:
Buildng Regs are guidelines only, and most more enlightened building inspectors will negotiate towards a solution, though it does sound as if Barnie's BCO was particularly mutton-headed.


Our building inspector was fantastic, he became my most valued ally during the project, but at the end of the day no 10 year damp proof guarantee and the building couldn't be passed.

My project was a stone barn which never incorperated any form of damp course, built into the side of a hill (field barn), after removing 2,000 tons of shale from the rear to uncover the rear walls I installed a land drain which obviously cured any water coming off the hillside, we came to many solutions along the way including upping the U value in other areas to avoid covering up our stone walls but the DPC had to be done, or rather I had to provide the relevant paperwork.

Barn restorations don't qualify for zero rated vat on materials, only a one off claim for vat at the end when building has been passed, as you can imagine that's quite a lump of money, not worth squabbling over DPC's when you need the vat money to add a conservatory Smile
Barnie

Here's some pics to give you an idea on the scale of possible damp problems.

Front of barn...



Rear..



Digging out..



Land drain installed with sewerage waste pipes on top...

Gervase

Nice place!
I'd imagine that the removal of all that shale and the land drain is what did the trick - it's what I would have done in the circs. In fact it's what we did do on our own place, having arrived to find one wall buried five feet into the side of a slope. It's now as dry as a bone.
A shame the BCO dug his heels on on the DPC but, as you say, in the overall scheme of things, it probably wasn't a huge amount to agree to.
With a conversion from agricultural use you can get contractors to levy VAT at 5 per cent throughout the work, provided you get them to invoice as such, with the words "In accordance with VAT notice 719 & 708, section 18.1" I've not had any trouble with clients who do this (and it makes life easier for me, too, as I end up sending less off to HMRC each quarter, while still claiming back the full whack on tools and materials that I have bought to do the work).
Obviously that means that the cheque you get back on completion isn't as hefty as it would be with 17.5 per cent VAT, but it means you don't have to spend so much up front - and you don't get interest paid on your VAT reimbursement.
Barnie

Thanks for your compliment Gervase.

The shale was put to good use - we built our access road with it, so it solved 2 problems in one hit, I love it when things work out like that.

The whole VAT issue with us proved more difficult due to not being VAT registered and actualy doing all the work including all joinery between myself/wife and a young 16 year old as my labourer. We had various accounts with builders merchants, plant hire and often sourced materials from odd places. Didn't use any contractors, the project was our full time occupation for 3 years...

I've had a look at your restoration and know only too well what it takes to do things right, so hats off from me

Can't resist showing you a couple more pics, very proud of what we achieved, as if you hadn't already spotted that Laughing

The cut roof was my masterpiece, all tusk tennons with pegs, here it is constructed on the floor as a dry run before dismantling again for final instalation up above..



Here it is partially installed



The finished barn conversion

Gervase

Cor, nice carpentry there!
I was working a few weeks back with a pal on a job where he was doing a roof like that, but using stud bolts. "Why aren't you pegging it?" I asked him. "Because no-one will pay for proper work these days - steel's the rule unless you're doing it for yourself or the taxpayer is paying. It should be pegged, but when I gave him the two prices, this was the decision, so there you go..."
And this is from a guy who worked for five years at St Fagans helping train their vernacular conservation team, so it's nice to see someone doing a proper job! You've every right to feel chuffed.
Milo

Gervase wrote:
The trench - known as a French ditch - is the most effective way of dealing with damp in older properties. The usual method is to dig it,,,,,

To what width and, relative to floor levels, what depth?
Barnie

300mm width is fine and 450 to 600mm below top of foundations at it's highest point, the trench needs to slop off all the way and idealy exit somewhere convenient, it can exit into a soakaway if necessary but best freeflowing out into a nearby drainage ditch, perforated pipe layed on the bottom of trench covered with drainage stone.

Differing ground conditions and underground spings can complicate things but generally the above will suffice.
Armchair

Great conversion Barnie and a beautiful roof Smile
Milo

Barnie wrote:
300mm width is fine and 450 to 600mm below top of foundations at it's highest point, .....


In which case I won't offer to dig the ditch for my elderly, wealthy next door neighbour who has what looks very much like ground water trickling into her cellar from about 1.3m below ground level!
Barnie

Milo wrote:
In which case I won't offer to dig the ditch for my elderly, wealthy next door neighbour who has what looks very much like ground water trickling into her cellar from about 1.3m below ground level!


Hmm, probably not a good idea to buy a new shovel just yet, sounds like candidate for tanking or an indoor pool Wink
Milo

Barnie wrote:
Hmm, probably not a good idea to buy a new shovel just yet, sounds like candidate for tanking or an indoor pool Wink


Laughing

Now explain tanking. I've heard of it, but don't properly understand how it works.
tahir

Wow Nick, that's a stunning place, brilliantly done.
Penny Outskirts

Stunning Nick Very Happy
Gervase

Tanking is where you apply an impermeable substance to the wall - either internally or externally - to stop penetrating damp. It's most commonly used with structures that are below ground level - in cellars or on walls that are built into the side of a hill, for example.
Ideally you want to do the tanking externally, but that isn't always possible.
Steer clear of any DIY stuff - you can get all sorts of bitumen-based paints and the like from stores, but they're all pretty useless. Ideally you need a sealed membrane or a proper waterproof render, and the usual materials used are Vandex and Newton 500, both of which will effectively seal the walls against water penetration.
Barnie

Thanks all for your appreciation, and appologies to Armchair for temporarily hijacking his thread Wink
Armchair

Barnie wrote:
Thanks all for your appreciation, and appologies to Armchair for temporarily hijacking his thread Wink


Not at all Smile Time to ressurect this thread...

I had a couple of damp proofing contractors in and they recommended (surprise surprise) an injected DPC. Now what they weren't aware of, and what I only discovered when chatting to my new neighbour this evening, is that the party walls (where the damp is predominantly found) is made of chalk rubble with brick piers. Probably a rather unusual form of construction but the row of houses is about 100 yards from a railway cutting so my neighbour thinks they used the free building material that was dug up there.

This begs the question, would an injected DPC be of any use and if not, what are the alternatives? Am I better off just leaving things as they are (on the basis that the walls have probably been damp for decades and aside from damaged plaster there don't appear to be any problems)?
dpack

all i can add is that underground water can be a real problem to deal with
above ground is as described above
MarkS

are there plenty of air bricks or have they been covered over. Im with Gervase on the whole no dpc injection thing.
Gervase

Chemical DPCs only work in bonded brickwork (sometimes!) - they most certainly do not work in rubble stone walls (it's down to something called 'viscous fingering' which means that the chemical takes the line of least resistance). If the contractors still recommend such a course once you've told them what the wall is made from, I would suggest politely showing them the door.
My advice would be to ensure a good air flow and to leave things as they are. Changes in drainage and ventilation are generally far more effective than mechanical treatments.
Armchair

I spoke to both companies this morning and both said that injected DPCs on a rubble/cob wall wasn't going to work.

Company A suggested a quarter inch thick dimpled membrane to full ceiling height with plasterboard internally.

Company B suggested tanking with a cementious plaster!

Neither of these sound appropriate. I think I'll stick with improving underfloor ventilation and plastering with a lime-based plaster.
tahir

You could try asking at AECB
Gervase

Armchair wrote:
I think I'll stick with improving underfloor ventilation and plastering with a lime-based plaster.

By far the best option - and the cheapest. It's best to avoid using any cementitious mortar or plaster on rubble or cob - it's not good for it.
Do check all soil levels outside to make sure they're a good six inches below internal floor levels, as well.
Milo

http://www.aecb.net/
Armchair

Any ideas on what ratio the plaster needs to be? I've been hunting around on Google for some advice but can't seem to find anything concrete (please excuse the terrible pun).
Gervase

One part hydrated lime (or lime putty) to three parts sharp sand. If you want a particularly smooth and hard top surface, use 1:1 silver sand and lime as a skim coat.
For more advice on cob, try to find a copy of Jane Schofield's Cob Buildings - A Practical Guide. You should be able to get it from Black Dog Press. Jane herself is hugely knowledgable and helpful, and is also the author of the indispensible Lime in Building - A Practical Guide.
If you're not far from Winchester, make contact with Bob Bennett at The Lime Centre at Morestead.
He runs courses in plastering and rendering and can also supply all the materials you might need. The site also has some useful fact sheets you can download.
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