Attic Chimney Breast - Brown Stains

sundin13

Hi, Our attic is a bedroom for our teenage son, heated and painted white. I repainted a couple of weeks ago as I'd noticed some brown stains on the chimney breast. It also seemed that the plaster was a bit damp so I gave it a coat of anti damp paint under the emulsion. I've been up there again today, and the stains are back. Could this mean that the roof's leaking around the chimney stack? And is that going to mean a massive bill?
Advice much appreciated

S13

CB1979_2

could just be the lead flashing needs replacing.

or the chimney repointed.

sundin13

The chimney has been repointed and rendered in the last five years, so the flashings sound like a more likely candidate. I will have to get the roofers out I guess. Thanks

CB1979_2

if you have a set of binoculars try and see if you can look at the chimney yourself to see if you can see it, before a roofer gives it the old "ooooh, looks a big job"

but if it's been repointed properly then i'd opt for the flashing needs doing, strange you didn't have that replaced at the same time as the repointing though, only takes about an hour and the lead isn't overly expensive (well wasn't when i had mine done!)

MX5huggy

Is the chimney used? If so it may be the damp is caused by condensation from the fuel burning.

David_Aldred

Hi,
Whilst looking for any defects regarding flashings around chimney stacks / defective pointing to chimney stacks / whether there are appropriate cowlings fitted to chimney stacks is obviously a good start to keep this area in a good state of repair, the following background information may also be of some assistance:

Chimney breasts are great when they are used for what they are designed for which is having a coal fire in constant use which keeps the area nice and dry. When this use ceases problems of dampness and disrupted plaster often occur.

In some houses a sheet of lead or other impervious material called a lead tray or damp proof course (dpc) is built all the way through the depth of the stack masonry just above roof level so that this acts as a barrier to moisture from rain saturating the chimney stack brickwork soaking down into areas below.

Do not confuse this barrier as described above with the usual lead flashings tucked into the chimney stack where it enters the roof as such lead flashing only tucks into the stack masonry a few millimetres.

However in many houses such a dpc barrier to the chimney stack was omitted because the thought was the heat from the coal fire would keep this area nice and dry which it usually did whilst the coal fire was in constant use.

When the coal fires cease and there is no barrier as described above, moisture can migrate down the masonry of the chimney stack irrespective of whether the roof / chimney stack flashings are in good order or not. In many houses this problem is not seen as the moisture evaporates into the attic storage space before it can be seen in the rooms below. However in this case directly below the roof covering is a room so any such issues will I am afraid immediately be seen.

Just to make things even worse the moisture that evaporates into the room from the chimney breast brings with it contaminates from the soot within the flues such as sulphates and once this occurs the plaster will not recover. These contaminates often present themselves as brown stains to plaster of the chimney breast and adjacent areas which will tend to come and go with the weather and the changes in relative humidity within these rooms.

Obviously the chimney stack / flashings / needs to be in good order along with appropriate cowlings fitted for any appliance below under the written guidance of a Gas Safe registered plumber but once the plaster is contaminated no amount of playing about above roof level will resolve the existing contamination.

Once the above issues have been addressed you can either put up with it / try and mask the issues as you have already but with limited success, or replace the plaster with a waterproof grade dry lining system over the full height of the area or re-plaster to a waterproof specification able to hold back these contaminates within the masonry.

The problem with such re-plastering is it requires a very high standard of workmanship for substrate preperation and application and the plasterer will want paying whilst the new plaster is still damp. Ordinary portand cement should be avoided within replacement plaster as sulphates will disrupt such. If the area degrades again in the future the plasterer may well not accept liability.

Because of these issues the waterproof grade dry lining is often the preferred option usually on a backing of studded polyethylene sheeting which goes under trade names such as Oldroyd / Platon / Delta etc. Specific cases will obviously differ from these general comments such that they should not be acted upon without proper inspection of the area of concern by somebody competent to do so but hope this helps, kindest regards, David Aldred Independent damp and timber surveyor

sundin13

Thank you David (and others) for the incredibly detailed response. The chimney is not in use, and although I haven't specifically had anyone look at the chimney flashings, I have had roofers up there doing other repairs and I would have hoped that they would have mentioned if the flashings were in need of repair.

We are currently in the process of selling the house, so I anticipate that any surveyor might make comment about it. However I actually find it reassuring that it may not be an active problem with the roof and that it may be able to be resolved in the way that you suggest.

iamcornholio

Brown stains on an internal breast are normally due to the acid created from the flue gas leeching through. If these stains are in the central region of the breast then this is what they are and you need to hack off the plaster, treat the wall with a barrier sealant and replaster

If these stains are near the ceiling then it's more likley due to defective flashings

eco-friendly_2

In extreme cases if no cure is found with common defects flashings etc, rendering the chimney is the only option.

David_Aldred

Hi Sundin13,
Further to my last post please be aware that as the flue goes all the way up the chimney stack the issues discussed can appear anyway on the chimney stack, even near the ceiling and indeed can appear more acute at the ceiling / chimney stack interface.

This is not only because of moisture coming down the masonry of the stack itself when there is no lead or other dpc and other issues as discussed above but in addition there is often masonry debris from the chimney stack and roof fine debris that over time has impacted between the chimney breast and the first rafter adjacent to the chimney breast immediately above the ceiling.

This fine debris is often high in contaminates as discussed above and may act as a hygroscopic moisture resevoir. Often the only way to see if such debris requires clearing out is if there is any minimal space loft void at ridge level you can crawl into to inspect this area or sample opening up the ceiling from below in this area. If the ceiling itself is affected close to the chimney breast areas then again it will not recover and replacement with foil backed plasterboard is often required making sure you include an impervious but flexible sealant between the plasterboard edge and the subject chimney breast.

If no such lead dpc tray is present then periodic application of clear breathable water repellants to the chimney stack would be preferred to rendering with cement based renders to older property chimney stacks (and indeed anywhere else) as they are generally too hard and dense for these types of substrate leading to premature failure, especially where there are likely to be issues of contaminates and thermal expansion.

Once cement renders crack they stay cracked allowing moisture to get in behind the render where freeze / thaw action causes detachment usually taking the outer face of the masonry with it and they tend to trap moisture rather than allowing the masonry to be breathable. In comparison a breathable true lime render tends to self heal as rainwater washes over them in the same way stalagmites are formed. Kindest regards, David Aldred Indpendent damp and timber surveyor