Damp: how far can it spread?

Paulie · 11 Oct 2008

Hi,

My mother's house is a mid-terrace 100 year-old property with a strange damp problem.

The ground floor rear wall has been damp for years and was skimmed a few years back. When decorating recently, we found the paper was damp and came off easily, as did the plaster beneath. I had a look at the gutter on the brick shed that butts up to the rear wall and found that not only was the fall was towards the house, the crud in it meant that the thing drained onto the rear wall of the house. I've replaced the gutter, making sure it drains correctly, and I'm happy I've sorted the cause of the damp. It seems that in the past, the symptoms had been treated rather than the cause.

Nothing unusual there but for the fact that there are signs of damp on the inside of the adjoining (party) wall in the same room. There is also mould on the party wall in the front room, about 5m away. When the nice neighbours let me have a look from their side, I found no signs of damp or any obvious cause for the moisture on my mum's side.

My question is this: When water penetrates a building, how far can it travel horizontally?

I'm wondering if damp can appear in two or more places with dry patches in between from a single source.

I hope so.

I would appreciate your thoughts.

P.

^woody^ · 16 Oct 2008

Generally, dampness in buildings does not travel far even if moisture is constant - it evaporates before it has chance to move along a wall or heads downwards, and can not travel up the wall as pressure is too low. But it could travel along the top of a DPC in the wall

Black mould is typical of a condensation dampness problem, whereas actual fungus and brown staining with white salts is a sign of moisture coming up or through the wall

Past damp can leave salts in the wall and plaster which attract moisture from the air, so affected areas should have plaster removed and replaced

It is possible for damp to have traveled along the wall like you describe, but it would normally take a lot of constant supply of water to do so, and a DPC to prevent it soaking downwards. However it would be rare for it to show as several damp places rather than one single big damp patch running along the base of the wall on top of any DPC

JohnD · 17 Oct 2008

if there is damp in part of a room, it can lead to condensation on other parts.

gday2uk · 17 Oct 2008

^woody^ said:
Generally, dampness in buildings does not travel far even if moisture is constant - it evaporates before it has chance to move along a wall or heads downwards, and can not travel up the wall as pressure is too low.

How about rising damp? The most common cause of damp in this age of building is rising damp caused by blocked cavities. The DPC is probably non existent being broken down slate.

I know the OP said the gutter was leaking against the building but there has to be a underlying cause (either single skin, blocked cavity etc) for the water to penetrate to the inside.

Best thing to do in this situation IMO is to call in the specialists. I know this is a diy forum but sometimes you just have to bite the bullet.

Paulie · 21 Oct 2008

Thanks for your replies.

Woody, I've seen the black mould that you describe - a patch on the party wall in the front room from skirting level to waist height which, given that is the warmest room in the house, isn't where I would have expected to find mould. Most of this patch is slightly discoloured with just a bit of black mould at the top.

There's no mould of any kind elsewhere, just the damp rear and party wall.

I've taken off the affected plaster and when I go back up there in two weeks time. I'll see if if the walls have dried at all with a view to replastering at some point.

Failing that, the bullet, as gday says, will have to be bitten.

BTW, Is there any chance the party wall has a cavity?

If so, I'm wondering if the moisture may be coming from above without affecting the neighbours.

memor maplin · 22 Oct 2008

You also might find that the back part of the building only was built half a brick thick, 4.5 inches ( something Victorian builders did)

dry lining should help.

Paulie · 26 Jan 2010

The back wall is now dry, indicating that the wonky gutter was to blame.

Since my last post we had to have the floors renewed. The tenants were about to lay a laminate floor when they discovered the boards and joists were rotten.

We got our friendly builders in and when they ripped up the old timber they found the cavity below was full of rubbish thus blocking the flow of air under the floor. Also, an air brick at the back was partly below ground level allowing water in when it rained heavily. This was sorted in the summer but the damp doesn't seem to have gone away.

We had a firm come and take a look and they want to strip the plaster in the affected areas and install a chemical DPC then replaster.

I was wondering whether it would be worth getting an independant survey done by someone who doesn't want to sell me something. Any idea how much this would cost?

mointainwalker · 27 Jan 2010

So is this the damp on the party-wall as previously mentioned ?

gday2uk · 27 Jan 2010

Paulie said:
found the cavity below was full of rubbish

Thought so.

Paulie said:
We had a firm come and take a look and they want to strip the plaster in the affected areas and install a chemical DPC then replaster.

Sounds ideal. Get other quotes from other damp proofing companies; some are just rip off merchants but you'll be able to tell who if you get more than 2 quotes. Good ones will offer insurance backed guarantees on their work as well.

Paulie · 29 Jan 2010

mointainwalker said:
So is this the damp on the party-wall as previously mentioned ?

Yes it is, athough there was no mention of damp on the rear wall when the letting agent did the routine inspection. However, the damp-proofing surveyor reckons most of the downstairs internal walls including the other party wall are affected although no mention was made of this after the inspection nor by the tenant.

Paulie · 29 Jan 2010

gday2uk said:
Paulie said:

found the cavity below was full of rubbish

Click to expand...

Thought so.

Hopefully, the clearing of this rubbish wiil allow proper ventilation and a reduction in the damp.

Paulie said:

We had a firm come and take a look and they want to strip the plaster in the affected areas and install a chemical DPC then replaster.

Click to expand...

Sounds ideal. Get other quotes from other damp proofing companies; some are just rip off merchants but you'll be able to tell who if you get more than 2 quotes. Good ones will offer insurance backed guarantees on their work as well.

I want an independant survey done. I suspect the findings were a result of a conductivity test on it's own without the other tests that need to be done.

Paulie · 29 Jan 2010

memor maplin said:
You also might find that the back part of the building only was built half a brick thick, 4.5 inches ( something Victorian builders did)

dry lining should help.

The damp has gone from the rear wall pointing to the leaking gutter as the cause.

Paulie · 10 Feb 2010

I had an independent surveyor have a look and he said the house needs more ventilation. He reckons that if the wrong materials are used on a house of this type, the plaster itself can exacerbate the damp by drawing moisture from the bricks and air. Once the plaster shows mould it's had it and will need replacing as its composition has changed making it prone to damp.

So, we're going to strip and replaster affected walls, (but not the rear which is drying since the gutter was fixed) using 3 to 1 sand/cement with waterproofer and fit an extractor in the bathroom and a larger one in the kitchen.

He says that modern fittings in a house of this age are sometimes overlooked as causes of damp. Plastic windows and doors along with central heating instead of open fires means ventilation is reduced and moisture levels increase.

Interestingly, he made no mention of rising damp, concluding that the moisture was airborne.

Looks like we've saved the cost of an chemical DPC and the tenants have been told how they can play their part, ie opening windows regularly and not using rads to dry clothes.

Nige F · 10 Feb 2010

Paulie said:
So, we're going to strip and replaster affected walls, (but not the rear which is drying since the gutter was fixed) using 3 to 1 sand/cement with waterproofer
.

Is that mix a bit strong

..I`d check with the plastering forum

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Damp: how far can it spread?

Similar threads