More damp!!

[kev208]

The survey on our house showed damp to the chminey breasts and damp to a partition wall. We knew the problems and went ahead with the purchase. I've sorted out the damp in the chimney as it was not ventialted properly and this seems to be on the mend. we thought we better get the professionals in so we had someone in last night.

He was actually baffled and is getting his boss to come and have a look. in several walls he was getting high readings right next to low readings and he also spotted some damp in places we had never even noticed and I'm sure were not there when we moved in.

i have a theory but its probably rubbish. its an end of terrace at the bottom of a hill, its got stone floors in the hall and back room and suspneded timber in the front room - the most damp is in the partition wall between these two areas. could it be possible that a lot of this is condensation casued by the recent hot weather combined with the contact with the stone floors?? another theory is that we are decorating the room above and have been using a steamer and a great deal of water.

any thoughts as to how these "patchy" readings could occur other than the damp course failing?

[Peter Parry]

Baffling dampdroid salesmen isn't very difficult at all. The "get the boss to have a look" is often a ploy used if they sense the victim is good for a big bill or they think they need some sales support.

That is because the meter does not measure damp. It simply measures resistance. They were designed for measuring the moisture content of _wood_ and they are quite good at this as there is a known and predictable relationship between resistance and moisture in wood. Typically dry wood will have a resistance of tens of millions of ohms, wood with a 25% moisture content about half a million ohms. These are high resistance readings.

When these meters are used in walls the readings are, by themselves, completely meaningless as there is no consistency in wall materials and no possible way of correlating a resistance reading with moisture level. Some common building materials will produce "damp" indications when completely dry.

The only thing you can say about them is that if the show dry it really is dry. Any other indication may mean the presence of surface damp or may mean any of a hundred other things. It is completely impossible to diagnose "rising damp" with one of these meters alone.

If insufficient "wet" readings are showing up the common salesdroid trick is to slide a finger over the prongs to produce the required "dampness".

This sound to be quite reasonable - all the meter detects is surface resistance - if you have been steaming the house the wall surfaces will, not surprisingly, be somewhat moist and their resistance low. The patchy reading would be consistent with this as the wall would not have been uniformly damp and will dry at varying rates.

See above. Moreover the obvious one is that the "measurement" isn't. The readings are meaningless so no conclusion as to how they might occur can be made.

If you can't see signs of damp don't worry about it. If you can then find out what's causing it (which won't be the DPC "failing")and fix it. Whatever you do, do not rely upon a "survey" done by a company which only makes money if it sells you a solution to the "problem" it will invariably discover.

[meow2222]

'ang about, this is someone who claims to understand all matters damp, but he doesnt know whats going on.

translation: softening you up for a hit

then its dry

did he notice damp or low resistance readings? Theyre 2 different things.

how would that cause damp? If there is any damp there would bne more factors invovled.

then youd expect to find damp temporarily!

if it has a stone floor it most likely has no dpc.

You need to take a step back and evaluate it properly first. Learn the signs of damp and survey it yourself. Ignore all this sales nonsense.

NT

[Chris Bacon]

Can you *see* the damp proof course? If you can, and there is a damp problem due to it failing, you will probably be able to see where it is failing quite easily. If you can't see it, you may have another problem. What's it (the DPC) made of? What sort of bricks (I assume) is the place made of? What sort of stone is the stone floor? How is the floor made? It's possible that it has bridged the DPC and that there's no vertical DPC. Was the house unoccupied for a while before you moved in?

[kev208]

No, and also not completely certain what to look for.

Victorian terrace, red brick dressed with local stone

Looks like concrete - I can see a blue plastic membrane sticking up at some points

Yes, nearly a year

Additionally, I spoke to a friend who is a surveyor over the weekend who said the plastering after the original DPC may have been done all the way down to floor level, and is in contact with the stone floor. I've had a look under one bit of skirting board and it doesnt seem to be the case so I'm stumped again....

there are two internall walls with damp (!) in them, one is almost below the bathroom which has had a leaking shower since we moved in (now fixed) so I am attributing this to that.

still doesnt explain the other wall....

[Chris Bacon]

Under the suspended floor (lift a board), and outside, you ought to be able to see a thick horizontal layer of mortar between the bricks where the DPC is, you may even see the edge of a piece of slate. If it's a slate DPC it should protude on the inside.

OK, it's not a stone floor, it's concrete. The blue plastic you can see is polythene DPC installed when the (comparatively recent) concrete floor was installed. This is a good sign.

Hm. "Ventilation". Your steamy stripping activities may figure, too.

The original DPC should be well below finished floor level.

Sounds OK then... are the skirtings nailed to a pair of horizontal battens, one below the plaster, one a little bit above the floor level?

I'd wait and see, or investigate the lower part of the wall more closely, since you can get to one side of it...

[kev208]

the internal wall in question is between the living room and dining room so I can get to both sides of it. the dampest part is right on the corner in the hall where the wall ends. it's so damp the wall paper is lifting off. however further along the wall (both sides) is dry to the touch (although damp according to dampman).

[kev208]

looked under floor boards. I can a think layer of what looks like thick material between the bricks about 3 incehs under the floor level. pulling at it, its like brittle black felt. there is a slate damp proof course in the back of the house but not here I dont think. the only other sign of a damp course is injection holes on the outer wall.

[meow2222]

dpc is very unlikely to be relevant here

NT

[Chris Bacon]

I'm having a bit of trouble visualising the layout.. can you post an ASCII art sketch, ot upload a diagramme/pics to some suitable site?

[kev208]

You are being really helpful so please don't stop watching this post. I'm away for the weekend though so wont be able to post anything until sunday at the earliest. i'll try and post pics and a sketch then

cheers

[kev208]

Update....

I'm working on getting some pitcures and a plan up but in the meantime and after some research I've got a theory of my own. I've lifted the wallpaper in various points on the ground floor and there is a definite tide mark virtually all around the downstairs room that has a recent concrete floor where the damp problems are concentrated. some spots are worse than others but generally the tide mark is about 2-3 inches above the skirting board so about a foot in total. In parts however it's higher (almost 3 feet).

my theory is the that the concrete floor is stopping natural evaporation and that all the moisture under the floor is being forced to the edges of the room and up the walls. does this sound realistic? if so, could it be that all we need to do is ventilate the skirting boards at various points allowing natural evaporation rather than the moisture creeping up the walls.

[Peter Parry]

Yes, quite reasonable.

Ideally you also need to do something to stop the water getting underneath if you can by improving drainage around the house. If this isn't practical your idea of allowing natural evaporation is a sound first step.

[Baz]

I have just read your original post. Quote "another theory is that we are decorating the room above and have been using a steamer and a great deal of water. " If you are chucking water around the house! No wonder you have damp. WTF do you think all that water has gone?

Baz

[kev208]

this was a few months ago now. a bit of steaming in one room is unlikely to cause tide marks all around one room. there would also be evidence of it running down the walls rather than rising up them.

thanks for the input though.

[Baz]

If I remember you had a cavity? Water runs down behind that and back from the bottom. Baz

[kev208]

No - no cavity. The tide mark is around all of the walls of the affected back room, it was the front room upstairs which we were steaming so only affects one, maybe two walls downstairs.