Damp Walls

[Nick]

Help Please

I am in the process of tidying up a small 150 year old brick cottage that was refurbished and damp proofed about 8 years ago. I did inherit a guarantee form the previous owner, so I didn’t worry too much about it at the time.

However, having now stripped the walls of decoration etc, I have found that there is a visible line of damp along the length of various walls at approximately 4 feet, just above the join on the plasterwork. It has been suggested by my surveyor that this could be due to salts in the brickwork! The plaster at the base of the wall is however visibly dry.

How does one overcome this problem as I am intending to paint the walls and this damp is going to be visually obvious, although it was apparently masked by the original wallpaper.

Any useful suggestions appreciated - other than re-wallpaper.

NC

 

[robgil]

hi nick , my understanding is that you cannot brush damp under the carpet and attempt to hide it , you need to get to the heart of the problem.
is this on an outside wall? is the wall rendered on the outside? do you have a leaking rainwater pipe?

 

[Nick]

Thanks for your prompt response.

It’s a 2up - 2 down cottage (with modern extension to back) and the damp is on at least 6 of the eight walls, including 2 internal walls, supporting the stairway.

The cottage is in good order and no obvious leaks. The walls are about 15" solid brick, with the original lime mortar between the bricks, however inside is cement & plaster, its rather strange as the damp is just in a strip about 6" deep along the walls, the top and bottoms appear dry.

Thanks

Nick

 

[MdB]

My thoughts:

Would I be correct in saying that the section of the wall that has been damp proofed is dry and that the section of plaster above it is damp?

If so, this would tell me that all that the damp proof coating has done is trap the damp in the wall. You now have a very damp wall all the way up to the top of the damp proof coating with the moisture escaping over the top. The damp proofed part of the wall is dry as the coating is doing a successful job of keeping the moisture in the wall and not letting it out. Think of the bottom part of your wall as a plastic bucket full of water that is overflowing at the top.

As it is a problem on internal walls as well, the source of the damp is probably from a high water table in the ground. I would guess that you have a concrete floor with a DPM of some sort in it. This is unlikely to go underneath the walls. Think of your bucket as having a hole in the bottom into which a hosepipe is connected.

Question: What are the ground levels like outside of the house compared to inside the house? I would guess that they are higher.

I am not an expert in this so all of the above could be wrong.

 

[Nick]

Thanks

The floors of the original bit of the house are wood with a gap of about 12" under the floor there are also some metal ventilators in the walls.

You step down out of the cottage and the levels outside are about 8-10" lower, although creeps up a bit around the extension.

Have just had closer look at plaster and it seems that some walls have been plastered from floor to ceiling, but damp only at about 4feet on some walls. Walls also feel sticky, but I guess that this could be from wall paper glue.

In under stairs locker there is no plaster on the walls which don't appear that damp other at right at bottom.

Where is damp likely to be coming from any ideas?

Other than that I don’t think I can tell you much more.

Nick

 

[MdB]

It looks like what I said above is likely wrong.

Where the moisture is coming from is the big question. The external walls could be from various reasons but it is the internal walls which are puzzling. It doesn't sound like it is coming up from the ground if you have wooden suspended floors.

Do you keep one side of the damp internal walls at a higher temperature than the other? Is there a damp side and a dry side? Is the damp side near the kitchen and / or other moisture source? I'm thinking condensation.

I'm a bit puzzled. We could do with one of the damp experts to comment.

 

[Penners]

I agree with MdB's suggestion that the walls may have been "damp-proofed" or even tanked up to a height of about a metre. This is the usual height to which such processes are applied. And I agree that it sounds as though the damp has "overflowed" this tanking.

As to the source - that's more of a puzzler. If you've eliminated all possible factors such as leaking gutters, dodgy pipes, roof problems, and so on, then two possibles remain:

1. That the tanking was applied before the walls had been properly dried out - thus trapping the moisture in the masonry.

2. That this is rising damp (which some people say doesn't exist - I'm not one of them!).

Solid brick walls will be much more at risk of becoming damp throughout, and - due to their thickness - remaining so for a very long time.

Solutions? Well, as I said above, your first move should be to make absolutely certain that the source of damp is not some problem with the building's water management facilities. Asuming you've eliminated that possibility, then I think you have to consider hacking off all the plaster up to a point above the damp area, and allowing the brick walls to dry out. This could take some months, particularly as we're approaching a wetter time of the year. Then, once the brickwork is truly dry, you could replaster in lime, and paint with limewash, distemper or a similar breathing paint.

 

[Lime]

Nick, as Penners says you have eliminate the water entering the wall.

This is the usual outcome of modern damp control methods being used inappropriately on an older house.
If the modern solution was correct for the situation the walls would be dry.
It appears from your comments that some walls are damp, e.g. the modern "plaster" surface and the brick low down.

Most modern damp prevention methods interfere with the way water is lost from older brick walls.
What you must understand is that older walls are designed to get damp and then dry out slowly.
Usually the walls are built so that rate of water acquisition is less than the drying out.
Anything that impedes the drying will increase the risk of damp.

A wall can be damp for many reasons.
Condensation.
A cooler wall in a warm house atmosphere will get damp.
The sign of condensation is black mould.
The answer is to ventilate the room so that the water can evaporate or not have the chance to condense in the first place.

Roof and chimney leaks bringing water into the house often directly down through the bricks.
The solution is to stop the leak which can often be difficult to find if a chimney is involved.

Gutter, downpipe or interior water pipe leaks soaking directly into the wall.
These can saturate a wall regardless of how well ventilated the room is.

Rain splash can cause problems too.
Make sure water is led away from the house.


High outside ground level, also a flower bed or addition to the house built on, can cause damp in the walls.
Replacing a wooden floor with a solid floor can also cause damp.
Covering the outside, inside (or both) with cement will cause problrms too because it prevents ventilation, doesn't stop rain entering and accumulating.

 

[Flyfisher]

2. That this is rising damp (which some people say doesn't exist - I'm not one of them!).

From what I've read, the assertion that rising damp doesn't really exist seems to arise from the observation that any water drawn up a wall by capilliary action (which does exist) will evaporate before it rises very high (and the higher it rises the faster it will evaporate dues to an increased surface area).

But, that assertion seems to assume that the walls are breathable and in this instance we know that's not the case because of the 'damp proofing' preventing such evaporation until the damp reaches the unproofed section of wall and then, as mentioned, 'overflows' or evaporates out of the wall.

If this is correct then the solution, as Penners points out, could be the removal of the damp proofing, allowing any damp to evaporate, always bearing in mind the 'one inch per month' rule-of-thumb for the time taken for a given thickness of wet wall to dry out. Once the new equilibrium has been reached, any residual 'rising damp' should be free to evaporate at the very base of the walls, hopefully below the level of the suspended and ventilated floors.

 

[Matt Green]

'evening.

How is the sub-floor finished? Bare earth? Does the under stairs locker have a suspended timber floor like the other rooms?

Sorry for the questions, but damp problems are horrible to deal with. Can you post photos of the symptoms? It doesn't sound lie condensation, it's likely that it is damp trapped behind cement that is rising to evaporate at the junction between the cement plaster and what was there before. The reason for it being there is more difficult to ascertain.

 

[Nick]

Thank you all for the various responses trying to respond to all questions asked.

Just to reiterate my previous postings, the property was refurbished some years ago and has no obvious external problems, gutters all new no obvious leaks.

Ground levels outside lower than the floors inside.

Earth under wooden floors appears dry. Floor under staircase wooden same as rooms.

I don't now much about damp, but is it likely to be condensation on inside walls, part of the old rear wall is now inside due to modern extension and damp also on staircase wall, again inside, I also thought condensation caused mould, there was no mould on the walls or the lining papers removed.

Having read the damp proofing report from previous owner appears that the walls have been plastered with cement and injected with silicone. Wall outside looks dry apart from lower bits near ground.

No damp visible on inside walls at low level only at about 4feet 'ish', although some areas appear to have dried slightly over the weekend, lining papers only removed latter end of week.

Have arranged for surveyor to look at problem on Thursday. NC

 

[Penners]

is it likely to be condensation on inside walls

Others have already mentioned that this is unlikely. Why would condensation occur halfway up a wall?

I still believe (as others do) that trapped moisture in the wall is the most likely cause. Cement and silicone are preventing the wall from drying out.

Your surveyor will be much more able to give you "on the spot" expert answers to your questions. I hope you're having a proper survey, and not just a mortgage valuation.

 

[Nick]

Thank you Penners

I already own the property, so the survey is just to look at damp issues (he's a friend of mine) otherwise will be calling damp company back to take their advice.

Incidentally would the damp not dry out through the exterior brickwork, there appears to be nothing to obstruct it?

Thanks to all concerned but I'm still none the wiser.

NC

 

[MdB]

Thank you Penners

I already own the property, so the survey is just to look at damp issues (he's a friend of mine) otherwise will be calling damp company back to take their advice.

Incidentally would the damp not dry out through the exterior brickwork, there appears to be nothing to obstruct it?

Thanks to all concerned but I'm still none the wiser.

NC

I wouldn't get the damp company back - there previous work hasn't worked so why would any (likely to be expensive) additional work be any better? (Most people here on PPUK have a very poor opinion of most damp companies.)

A few pictures would help. You should also have a look at the damp FAQ here if you haven't already.

 

[Penners]

I agree with MdB about getting the damp company back in. They have a vested interest in blaming some new factor for the damp, and may try to sell you some additional magic treatment. I suspect the chances of their admitting that their interior tanking might be responsible for your damp line are... ahem... slim.

If your friend is properly qualified on damp matters, he's your best bet.

As regards the damp drying "outwards", this is a possibility. But if the inner part of your solid brick wall is the dampest part, then the moisture could take a very long time to migrate out to the exterior. Once it's there, of course, then its ability to dissipate will be considerably affected by the ambient temperature and humidity. And, as you may have noticed ( :wink: ), the UK gets a lot of rain, so the ambient air is often laden with moisture already.

What's the pointing like on the exterior of the wall? Which way does the wall face (on the compass)?

Thanks to all concerned but I'm still none the wiser.

I think if you look back on the responses you've had to your question, there's a considerable amount of information to be found in them. Of course, none of it can be stated categorically - as Matt says, damp is very tricky to diagnose even with a full on-the-spot physical inspection. So on the basis of a brief written description it's doubly difficult.

But you've had some informed and worthwhile speculation.

 

[jaykayem]

Nick,

I posted recently regarding my brick wall damp problem, and received a great deal of help, some of which you may find useful:

http://www.periodproperty.co.uk/forum/viewtopic.php?f=1&t=10546

 

[floramarg]

Hi, I'm reading these posts with interest and whilst I cannot comment on the problem or offer any solutions, I do have my own query and wonder whether anyone has any feedback.
A bit of background info - I have recently bought a 100 year old terraced house. The rendering outside was down to the ground, I have since removed this hopefully resolving the problem of damp inside the house. The previous owners have obviously had some damp treatment done because you can see the holes in the bricks(i have no paperwork for this). I have removed the plaster from the walls, as it was practically hanging off anyway, so now am back to bare brick which I intend to plasterboard.
The kitchen was extremaly damp with noticable black mould on the walls. Again, I have removed the plaster and now the bricks appear to have dried I intend to plaster board. I am also in the process of digging out the old floor in the kitchen - this having been some kind of ash/soil/sand concoction. I have sought advice and will re-lay the new floor with the appropriate materials.
My query is regarding the floor in the adjoining room. The floor seems to be concrete, maybe 1" think or so and under that seems the same as in the kitchen (so I assume original). the concrete floor in the dining room has a perfect 'rectangle' shape (just the outline of the shape), which shows up only when it rains. This come up on the other side of the petition wall from the kitchen to the dining room. I have no idea where the moisture would be coming from???????

 

[Penners]

If I understand you correctly, you have a concrete floor which exhibits a perfect rectangular "shadow" on its surface, whenever it rains. I presume this shadow is darker than the rest of the floor?

If so, I wonder whether you might have a well or a sump under the floor. If this is the case, then the apperance of this shadow would suggest that it's not very effectively covered, so might need some inspection/attention.

I'm afraid the only way that you'll find out for sure is to dig - unless you have access to any old records of the house that might mention anything.

 

[Nick]

Following up from my last posting.

I have now had my friendly surveyor and an Independent Damp Surveyor look at the property and the strange line of damp around the various walls.

Salts in the wall is apparently the cause, this occurs as damp rises in the wall and dries out! The salts apparently originate from the ground as the damp rises through the wall.

The wall itself appears dry, although the salts attract damp from the air creating the visible damp line. Apparently its called a ‘Salt Band’.

May have to replaster the areas concerned.

Thanks for all previous help

N

 

[Penners]

If you're going to have to replaster that area, then you'll obviously have to hack off the old plaster.

If it were me, I would still take the opportunity to leave that area unplastered for a while, to allow any residual moisture to dry out.