Advice needed re: damp (again!) and woodworm

chicarg

Thanks again, it is all really helpful.

Apparently the DPCourse previously done has been applied 160 mm over ground level and that’s why the surveyor called to our attention.

I was just reading about the DPM and it seems like something you apply to the floorings, can it also be applied to walls?

Would anyone have a rough idea of what will be cost to have a new DPC done or a DPM done?

And TJ are you in the London area by any chance?

chicarg

frannyscho wrote:

Have a look at period house forum. Most damp is dealable with by the most obvious means, and damp courses are a waste of time anyway. Have a look at some really bad damp and death watch beetles too and feel reassured. They have oodles of practical advice there.

I did look at the In my Home (includes DIY) forum but could not see a Period house forum?

matto

One problem I have often found is that internal plaster (where walls have been replastered) extends below the DPC and then acts as a bridge over the DPC to allow damp to rise up the wall.

I thought the higher the DPC the better although obviously there's a limt as below the DPC is liable to be damp.

My slate DPC is about 60mm above ground level and works just fine (in a well ventilated and well heated house).

TJ27

I'm afraid I'm in South Wales!

A DPC (Damp Proof Course) is what's found in walls, built into the brickwork. It's usually a plastic or bituminous layer simply bedded in a mortar joint about 150mm above ground level. An injected DPC is a silicone solution I think, which soaks into the bricks and does the same job. (In theory that is, the effectiveness varies and some other posters clearly think they are useless. I'm not entirely sure about that but essentially I would probably agree with them.)

A DPM (Damp Proof Membrane) is usually a sheet of polythene which is typically laid under a concrete floor slab and perhaps lapped up the walls slightly. In fact it's often lapped throught the wall to form the DPC too. In modern building it can serve to act as a radon barrier and all sorts.

Basically a DPC stops moisture soaking up the walls, a DPM stops moisture soaking up through a solid floor.

Older buildings sometimes have a slate DPC, which breaks down over time (not sure why though.) They sometimes have a crude form of DPM, like a layer of bituminous paint, but not often. Sometimes they have neither DPC nor DPM.

Dunno about cost really but a new DPC and/or DPM are both quite disruptive jobs to do. If they are done properly that is. You wouldn't want to be living there when the work's going on!

mrsS_2

hi-my first house(20 yrs ago)was an old victorian property- with woodworm and damp guarantees.

however the vendor had used the wrong sort of plaster over the silicone injected damp proof course so although i got a guarnatee when i moved in i couldnt claim on it-

so when the survey picked up the damp- the vendor waived the guarantee and everything was fine - until the wallpaper went black and peeled off the walls after 6 months.....

we had to have the whole house re- injected and replastered (properly this time) and it cost about £1500 20 yrs ago- so whatever you do wait for the quotes to come in!

TJ27

Yes, in my experience many builders guarantees are not worth the paper they are written on.

Typically, for a damp course you have to hack off the plaster up to a metre height, inject the DPC and then replaster using a very specific mix and thickness, usually 25mm or so. The trouble is that above 1 metre height the plaster might only be 12mm thick. So of course the builder will make the new plaster match the old and it will be 12mm thick. But I've heard of damp companies saying that the guaranteee is invalid because the new plaster (or render usually) is not to the thickness specified. There is always some sort of get out.

There are all sorts of pitfalls. What if the builder doesn't exist in ten years? Some offer insurance backed guarantees but I'd even be a bit wary of these to be honest. I'm afraid it can often be extremely difficult to find a builder you can trust to do a good job. But I'm sure everybody knows that!

A problem with injected DPCs is that they depend on the bricks sucking up the silicone and forming a barrier. Now of course if the bricks are already damp and partly saturated with water, then they aren't going to suck up a lot of silicone. It stands to reason that an injected DPC isn't going to work very well if the wall is damp in the first place. You can dry the wall out in good weather or use a dehumidifier perhaps, in theory, but an injected DPC is never going to be as good as the original one.

BobProperty

TJ27 wrote:

....They sometimes have a crude form of DPM, like a layer of bituminous paint, but not often.....

I believe it was hot poured on to the brick course.

TJ27

Yes, I think yours is probably a more accurate description Bob. And wood block floors for example were bedded in bitumen, which stuck the wood to the concrete. This had the added benefit of being a DPM at the same time. Of course over time the layer becomes brittle and cracks at the slightest movement and the blocks come loose.

Modern materials are better but actually I stuck down some of my wood blocks only the other day. I've got a 1930s semi. What did I use? A bituminous emulsion. So perhaps things haven't actually changed that much!

chicarg

Hello all!

We are learning a lot about damp proofing! Thanks!

So we have spoken to the EA about the issues raised in the survey to see if the vendor has guarantees of the previously done DPC. If he does, we would want him to deal with the company that did the work before exchange as suggested in case any problems arise with the guarantees (as previous posters)

The EA said they are going to get a damp & wood specialist in: Kenwood Plc, has anyone heard of them? I googled them yesterday and reviews seem good but since it is the EA who is getting them in we are a bit sceptical about their “independent” advice.

They will provide a report on any work done and quote us for costs. With that we can then get back to the seller and see what happens… maybe renegotiate?

blossom385

Just been reading the threads. Just a quick note about the insured warranties on damp proofing. (for those of you that don't know what these are, they are warranties that you can take out - for an extra fee of course - so that if your damp proof installer goes out of business and your damp proof fails the warranty company will step in and put the work right free of charge) However, beware, many of these warranties are owned by the chemcial companies and (so I have heard) in the event of a claim say it was down to bad workmanship which wasnt covered. There is an Insurance policy that you can get with the GPI This is an independant insurance company regulated by the FSA and Insurance Premium Tax is payable. They will only cover work carried out by Qualified surveyors. (when choosing a damp proof installer it may be prudent to see if they offer this insurance) If you claim, the insurance will cover both chemical failure and poor workmanship.

to tell the difference between a warranty and a genuine insurance policy ; Warranties charge VAT at 17.5% insurance pollicies charge IPT at 5% (Vat is not applicable on genuine policies.)