leaking chimney

[Anonymous]

Our house has two chimneys, one is a more recent brick affair, the other a large rubble stone which lets a lot of water through to the flue when the wind is blowing the wrong way. The mason we are using who is very competent, is telling us that repointing will not be enough to prevent the problem, the lead flashing has been taken out and refitted into a new deeper slot in the stone, but the problem seems to be that the stone is very poor quality almost slate like which our mason tells us is notorious for allowing water in if it is not very carefully laid. The options we seem to have are, take the stack down and rebuild in better quality stone, render it using a cement and lime mix with a waterproof additive, or rebuild in blue brick to match the other one. The house is 17th century in origin, in very exposed position in North Wales. no listing. Cost is an issue therefore render would be our preference. Anyone have any thoughts?

 

[Nemesis]

render it using a cement and lime mix

Can I ask who has suggested this?

 

[Ian Bond]

Rebuilding sounds excessive to me, and a measure of last resort.

Proper repointing may help (without OPC), once you've fixed the soakers and flashing.

Does the chimney have pots fitted? Just wondering if the flaunching around the pot's cracked and is letting water in.

 

[Anonymous]

Thanks for the responses. The flashings are all fine there are no pots as such, just short ventilated caps which are all ok, the chimney has been checked by playing a hose over it and inspecting from a hole made in the flue inside the roof, the problem is that the stone itself is allowing driving rain through not the pointing, (which was replaced quite recently) We have talked to our builders again today and they are planning to use a waterproof slurry followed by a several coats of silicate masonry paint which will allow us to keep the original stack appearence albeit painted to match the rest of the walls.

 

[Nemesis]

It could also mean that any damp is trapped and the chimney deteriorates rapidly.

We have talked to our builders again today and they are planning to use a waterproof slurry followed by a several coats of silicate masonry paint which will allow us to keep the original stack appearence albeit painted to match the rest of the walls.

Sounds drastic and short term to me.

What was the pointing done in?

 

[Matt Green]

the problem is that the stone itself is allowing driving rain through not the pointing,

I never like that diagnosis, it smacks of 'it can't be anything else I can think of'. Think about it for a second: so much rain has to hit the stone for the inside surface to become not just saturated, but dripping wet. Or the rain to be so hard that it passes through solid stone.

Has this flue got a metal liner?

 

[MdB]

Think about it for a second: so much rain has to hit the stone for the inside surface to become not just saturated, but dripping wet. Or the rain to be so hard that it passes through solid stone.

My house is made from the worst type of sandstone possible. It is so weak that you can break it apart in your hands and it soaks up water like a sponge. Drop a bit in water and it bubbles for ages as the water seeps in. I'm sure the outer surface of our wall is saturated a lot of the time but the inner surface is bone dry (at least it is now the cement render has been removed). I'm with you Matt on this one, I doubt much water is going through the stone as if anyone would have this issue, we would and we don't.

 

[Nemesis]

Our chimney used to leak through a wall at times, in conditions of driving rain. This was the single skin part of a rubble stone wall, at the back of the opening.

Traced to small cracks in the (nasty cementy) pointing. A previous owner was very fond of nasty cement, unfortunately.

I doubt it's the stone either. I supect that there is a less damaging solution than cement render, too, and I would be suspicious of any builder who recommended cement, or any type of waterproofing out of a tin.

What exactly are the symptoms of the rain coming in?

 

[Anonymous]

Thanks to everyone for your comments. The stone is some sort of slate which has badly delaminated in places hence the water coming through the stone rather than the pointing, which you can actually see in places from inside the flue. The chimney was repointed in A strong lime mortar against the advise of the company who are now working for us again, the pointing is intact. We can't really see any other way of curing this without taking the chimney down and rebuilding and as the builders are doing great work in other parts of the house I don't really feel inclined to question their judgment.

 

[Nemesis]

Well if you are going to render, why not render in lime?

Sorry and all, but waterproofing slurries etc and historic structures are not really compatible.

Don't let anyone near a period building with cement, and cement lime mixes are really not recommended either.

 

[skier-hughes]

If the chimney is made of delaminating slate which is letting water through I'd be worried by the safety of it falling down.
I'd opt for rebuild.

 

[rocky]

What is the flue construction?

 

[Anonymous]

Thanks again for your comments. I would just point out to nemesis that waterproofing slurries are quite common on stone houses in this part of Wales, we have been to look at a number of other houses which have had the same treatment and now have no leaks or damp problems, so we are hopefull that this will be the answer. The use of lime as opposed to cement , well all I can say is you have to eventually put your trust in someone and in this case we have decided to go along with the builders. We have always lived in old properties and all of them apart from this one have been either rendered with cement or pointed with it with no problems at all, I am not suggesting using lime would not be beneficial but I do think that in certain situations cement works just fine.

 

[Nemesis]

Well all I can say is a disagree with you, and I suspect anyone with much idea about how to treat period buildings would disagree with you.

In the long term waterproof slurries and cement cause all manner of problems with traditional buildings.

http://www.oldhousestore.co.uk/tech_ohs/limeintro.html


Maybe you should give SPAB a ring.

http://www.spab.org.uk

http://www.buildingconservation.com/articles/mortgage/mortgage.htm

http://www.historic-scotland.gov.uk/inform_lime_and_cement.pdf

http://www.cadw.wales.gov.uk/upload/resourcepool/masonry%20notes%20english7511.pdf

http://www.vcrestorations.co.uk/intro.htm

http://www.horganandwebb.com/

The latter is the website of Gervase, who posts here.

This is his house in Wales:

http://www.periodproperty.co.uk/ppuk_discovering_article_042.shtml

 

[andrew gayton]

Thanks again for your comments. I would just point out to nemesis that waterproofing slurries are quite common on stone houses in this part of Wales, we have been to look at a number of other houses which have had the same treatment and now have no leaks or damp problems, so we are hopefull that this will be the answer. The use of lime as opposed to cement , well all I can say is you have to eventually put your trust in someone and in this case we have decided to go along with the builders. We have always lived in old properties and all of them apart from this one have been either rendered with cement or pointed with it with no problems at all, I am not suggesting using lime would not be beneficial but I do think that in certain situations cement works just fine.

good grief. how very wrong you are.

 

[andrew gayton]

WHAT IS WRONG WITH CEMENT MORTAR?

Modern cement pointing is very different from lime mortar. It is hard and brittle, much less porous and sometimes completelywater-proof. Its use on traditional masonry is damaging in several ways.

Cement pointing is harder than soft brick or stone and is too rigid to accommodate settlement or movement in the wall. When movement occurs the edges of the stone or brick are forced against the hard mortar spalling the masonry and cracking the mortar itself.

Further damage is caused by rainwater seeping into the cracks in the pointing and around the edges of the stones. Because the mortar is not permeable this moisture cannot evaporate from the mortar joint once rain stops. Instead it is forced to evaporate through the face of the brick or stone and soluble salts present in the water crystallise in the surface layers of the masonry leading to crumbling and decay. This is sometimes so severe that the entire face of the stone is lost and the hard cement pointing is left standing proud. Further rainwater is trapped and the decay continues. The concentration of trapped water in the masonry also increases its susceptibility to frost damage in winter.

In contrast soft lime mortar allows moisture movement and, being more porous than the masonry, encourages evaporation and salt deposition in the mortar joints. Thus it is the mortar which decays and not the stone or brick. It is much easier and cheaper to repoint a wall than to repair or replace damaged brick or stone, and there is less loss of important historic fabric.

Cement render causes slightly different problems. Hairline shrinkage cracks inevitably form in the surface of the render as it sets or afterwards by slight movement in the wall. Rainwater is drawn by capilliary action into these cracks and then diffuses into the wall. Once inside the wall this moisture, together with any rising damp, is trapped as it cannot evaporate through the hard, impermeable render. Moisture levels start to build up in the wall and the moisture tends to diffuse towards the inner surface of the wall resulting in internal dampness and damage to plaster and decorations. So, strange as it may seem, applying a waterproof render can actually increase levels of damp inside the house. A porous lime render encourages evaporation of moisture from its surface, helping to minimise the effects of penetrating and rising damp.

etc etc etc.

 

[skier-hughes]

Well all I can say is you have to eventually put your trust in someone and in this case we have decided to go along with the builders. We have always lived in old properties and all of them apart from this one have been either rendered with cement or pointed with it with no problems at all,
.

I agree you have to trust someone, but it may not always be well placed.

Maybe you haven't lived in your previous properties long enough to find the problems with cement. New cement render will be fine for a number of years, until it starts to crack, a small crack starts to let in moisture after a few more years there are damp problems, where people 3/4/5 moves down the line have to remove all the cement render, repair and replace with lime.

I'm only a short time period property ownder, but I'm now a non cement on my house kind of a guy.
Graham

 

[Anonymous]

Thanks again for all the comments. We have done a lot of reading and do understand the benefits of using lime in old buildings, I should have pointed out that we are having several rooms plastered using lime putty, and all the masonry repairs have been done using hydraulic lime. At the end of the day the chimney probably will need to be taken down and rebuilt, so this decision is mostly based on short term finances and doing something to stop the immediate problem. The points regarding damage to the stone do not apply as the stone/ slate is already badly damaged through presumably exposure to centuries of wind rain and frost, nothing to do with cement. As for our previous houses, as far as I am aware the external render was put up in the 1950s and is still there, our other property which was part timber frame was re plastered right through in the 1970's and was fine, no cracks no damp, maybe we have been lucky :?:

 

[Gervase]

The slate in your chimney may well be damaged - some of the slate in my house was like a wet book to the touch, thanks to cement render and deficient pointing - but a cement slurry with added waterproofer and silicate paint is just what will completely destroy it.
Slate as a building stone is very prone to delamination because it can trap water between its 'leaves', which is why it should always have some sort of protective but breathable coating. On normal walls limewash is enough, but on exposed areas - and chimneys are certainly exposed - a breathable render is needed. What you should never do is put on a finish which will trap the moisture and accelerate decay.
If you put a cement slurry finish on then you'll see happen what has happened to hundreds of houses in Wales. The stone will deteriorate to mush, up to the point where the only sensible option is to rebuild the chimney using blocks or bricks. I've got a chimney like that, which was replaced about 15 years ago. I was warned that the other one was on the way out - and it was, until I removed the cement render, repointed with lime and limewashed it. It's now weathertight and good for another century or so.
As others have said, if you use cement you may find you have no problems for five years, or even 10, but you're storing up trouble for the future. If you don't intend being in the house longer than three years or so, fine - leave the legacy for whoever comes after (and hope they don't appoint a surveyor who knows about stone houses), but if you're in it for the long haul, do it properly now. It's cheaper, long term, and your house will be the better for it.

 

[Nemesis]

all the masonry repairs have been done using hydraulic lime

Not always the best option - especially if it is strong hydraulic.

Non-hydraulic is still probably the best choice in many circumstances, although for a chimney a weakly hydraulic is probably a useful choice.

Just adding this for general information!