Damp spots and independent gurus...

[Geoffrey]

Well I guess scientifically I can't - but the algae growing on the stone floor (see other thread) I think is a fair indicator.

 

[NT]

Congratulations, NT, on the successful deployment of a quotation (even if the embedded emoticon didn't work )

Well thank you I know what it is now, just dont always remember to tick it.


NT

 

[biffvernon]

but the algae growing on the stone floor I think is a fair indicator.

Algae on the floor might get it water from below, through the stone, or it might get it from the air. A stone floor will usually be the coldest surface in the room and the most likely to attract condensation. But what about the wall?

 

[Geoffrey]

Yes walls are still a bit damp around the bottom 18 inches or so, but as I said it is improving gradually. I removed 3 or 4 inches of concrete and dpc off this floor last year - as the floor wasn't breathing moisture was being forced into the walls. The floor now breathes and a couple of spots of algae to control is a small price to pay.
Presumably there was a damp problem 30 or 40 years ago when the concrete was laid - but I'm sure it can be controlled in a better way.
Ground levels outside have been lowered and drainage improved. This year the roofing and guttering are being overhauled (not actually relevant to this room) - it all helps. Next year I'll be having a go at the walls throughout the ground floor - removing emulsion, paper etc and patching plaster as necessary and decorating using breathable paints and hopefully the house will be stable in terms of moisture.
Another bit of damp treatment from the past I've inherited is concrete skirting boards - I might keep these as they're now part of the history of the building - and doubtless very messy to get rid of. I figure if the walls and floors are breathing then a few inches of concrete probably won't be making too much difference.

 

[Lime]

Children should not be allowed to leave school until they have learned by heart (and really understood the meaning of) "There's no such thing as a free lunch".

Some of the local secondary school children only go to school to get the free lunch. It makes a change from nothing or take-away at home.


As far as damp in old walls is concerned, I have found that cement placed on a wall never improves the situation.
The concrete skirting boards would go if it was my house.
Lowering the outside ground level nearly always produces an improvement as well as opening windows regularly.

 

[Matt Green]

The presence of algae means that this is almost certainly not a rising damp problem.

Ground water rising through the walls and floor will mobilise salts as it moves along an evaporation stream. The salts (mostly chlorides and nitrates) inhibit the growth of moulds and algae.

Whilst I would disagree from experience that 'most' damp problem in period buildings are due to condenstaion, this one sounds likely. If there is a damp problem in the base of the walls too I would need to know how the junction between the wall and the floor is constructed. There may be more than one source.

As for the original posters problem, you have to ask what's behind the wall on the neighbour's side- without that information it's tough to come up with any meaningful diagnosis.

Calcium carbide tests are curious. They seem to be used by remedial companies in guarantee disputes, mostly, although I think Rentokil may be using them in normal surveys now. I've probably posted this before but they are working a long scam, the theory of which goes like this:

The chemical DPC is guaranteed for 20 years. As part of the BBA certificate the DPC must be used in conjunction with a proprietry plaster system. The BBA certificate covers both the chemical and the plaster. The plaster is guaranteed for a statutory fit-for-purpose 6 years.

A surveyor uses a resistance meter to check a wall is damp. He finds high readings and writes a report suggesting the cause of the readings is rising damp that can be remedied by the installation of a chemical DPC and replastering.

The work is done and the damp problem returns. The contact the company and pay their fee to have them come out and check the efectiveness of their DPC. They use a calcium carbide meter this time, rather than a resistance meter. Hey presto- this time the wall is dry therefore the DPC must be working correctly (......) and claim is not upheld. Although you might get a replastering quote.

We don't use a calcium carbide meter in our damp surveys. There are several reasons; we drill a column of holes up the wall at 250, 500, 750, 1000, 1500 and 2000mm, remove the drilled samples and seal them in airtight phials. We take them back to the lab and weigh them wet, dry them and weigh them dry. This gives us a free water content. We then put teh samples in a salt chamber to see how hygroscopic they are (how much water the wall is absorbing from the atmosphere).

Yes, it's destructive. No, it's not used very often in pre-purchase situations. It does, however, give a moisture profile of the wall up to 2m rather than at a specific point; it gives a hygroscopic profile which helps determine the source and severity of ground water movement and it tells you which way water is moving. It also doesn't generate a large amount of stinky waste.

Invasive damp surveys tell you far more than non-destructive methods, but you have to tidy the walls up afterwards. Calcium carbide tests are a good tool, but if you are going to be destructive to may as well go the whole way and use the oven/dry method as it tells you a lot more.

So there you go. And if you're still awake I admire your tenacity- just don't start me on wood-boring insects.



Matt Green
-wild at parties.

 

[Nemesis]

Actually I enjoyed your article about wood boring insects...

http://www.ridoutassociates.co.uk/article02.htm

but I'm great at parties too.

 

[Geoffrey]

[Ground water rising through the walls and floor will mobilise salts as it moves along an evaporation stream. The salts (mostly chlorides and nitrates) inhibit the growth of moulds and algae.]

Damn! If I'd just left the ground level high I'd have enough salts still coming through to stop the algae. [/quote]

 

[plumbers mate]

There was a tv prog the other night where a damp patch was caused by the body walled up behind it .............

 

[Penners]

We remove the drilled samples and seal them in airtight phials. We take them back to the lab and weigh them wet, dry them and weigh them dry. This gives us a free water content.

I must say, Matt, that seems a much more obvious and straightforward way of testing.

 

[PC]

I would agree with Matt that condensation in period buildings is not that common and not something I have come across as the main cause of complaint!

On the subject of Calcium 'Speedy' Tests, yes they can be a usefull tool to aid with diagnosis assumming that you can carry out a destructive survey in the first place. I rarely use this on site as it can be quite messy.

But if your looking for accurate assessment then I use moisture profiling (not to be confused with the profiling the government are trying to introduce) by drilling samples and testing them back in the Lab.

However again it is a destructive method of investigation and not something Ive ever been permitted to use (by a Vendor) when surveying for a prospective purchasher. Would you want rows of holes drilled up your wall?

PC

 

[Nemesis]

Sadly, PC, rows of holes drilled all over the place is what most folks end up with when someone decides, by the non-destructive moisture meter test, that there is 'rising damp,

It's not usually a pretty sight.