Brickwork damp patch after prolonged heavy rain

[Mr Punter]

I think it would be normal to have a stepped cavity tray installed above the stepped lead flashing, but not an option retrospectively.  Can you consider coating that damp wall with Stormdry Masonry cream?  I have used it in the past and it works really well at repelling water and leaves the brickwork breathable.  It soaks in and apparently lasts over 25 years.

 

I am using it on a forthcoming build where there is an exposed brick section that will be difficult to access in future.

[PeterW]

43 minutes ago, readiescards said:

The dummy pots sit on  concrete tiles built into the top lip and then surrounded by a concrete bed. Below that tile is a void and below the lead tray is another void.

 

That should have had a DPC with weeps built in - has the lead tray also got weeps..?? And what is the lead sat on ..??

 

If those are dummy’s then I would have stood them on a DPC square and then put a hole through the bottom edge running back toward the roof to allow any moisture to get out. 
 

Looking at that, there is water getting in at multiple places - could even be coming in via the stepped flashing and into the void. 
 

Does it have some sort of corbelling to stand on the inside wall of the build as it’s too wide to just be part of the external wall..?

 

Do you have access to the brickwork from the attic space ..?? I would be taking a couple of bricks out from the inside to get a camera into the void to see where is wet - that will give you an indication of where to start looking for the problem. 

 

[readiescards]

One half of both stacks (about 10 brick courses below the lead tray has been coated by some water proofing - which has made the outer wall look an ugly patch work of differences (especially with part of the stack being rebuilt, in a previous attempt).  The waterproofing/rebuild/insert of another cavity tray of the left stack has stopped damp coming  into the attic space.  There are weep holes above the lead tray and cavity tray.  I'm told the soaked looking brickwork below the water proofing is simply the water that has run off the water proofing but I find that hard to believe that it can then enter the utility attic space.  

 

Prior to rebuilding the stack an investigation was made into the left stack and this reveal wet internal blockwork.

 

I don't know what the lead tray is sat on

 

DPC with a weep hole directly below the pots would seem a good idea.

 

The right hand stack continues to have internal damp issues (it has had the pots removed, resealed and reseated) - that is the big damp photo (I don't know how to place photos in the text where I want them, sorry)

 

The attic photo with the blue box shows the damp from the left hand stack soaking into the utility attic space.

 

The stepped flashing has been inspected, not by me, but I'm told is in good order.

 

Yes both stacks are corbelled - last photo.

 

[readiescards]

Right hand stack yesterday, you can see below the lead tray where the brickwork has been painted with moisture proofing - the bricks looking dry.  But below that the bricks look very wet - a few days after the rain the rest of the gable will dry normally but a strange V shaped patch of brickwork will remain wet for a few more days.

[Mr Punter]

I would coat the whole of the flank walls with Stormdry.

 

Off topic, where were your stooled window cills from?  From the photos they look well made.

[readiescards]

On 29/12/2020 at 10:42, Mr Punter said:

I would coat the whole of the flank walls with Stormdry.

 

I've previously been advised applying an external waterproofing is merely a sticking plaster and last resort as really it masks the true issue plus it only has a finite life span, so kicking the can down the road as such.   Is a waterproofing such as Stormdry, a permanent (25-50 years) solution that does not cause any knock on issues?

Thanks

 

[Bonner]

I have seen this before, waterproofing causes the rain to run off so it soaks the untreated brickwork below. Treating the whole wall may be the only solution.

[TonyT]

Do you have an architect drawings of the area?

 

just to see some of the detail?

 

don’t apply an external waterproofing solution, it’s masking the problem

[readiescards]

On 05/01/2021 at 11:24, TonyT said:

Do you have an architect drawings of the area?

 

just to see some of the detail?

 

don’t apply an external waterproofing solution, it’s masking the problem

 

No detail architect drawing of that area, the architect drawings were for planning approval only and the builder just 'built it'.  I will try to create a diagram from my understanding of what there is.

 

Although the waterproofing has been applied to a bit of the chimney as a last resort I do still feel it was a last ditch attempt as nothing else seemed to work and it is indeed hiding the real problems 

[readiescards]

On 05/01/2021 at 08:42, Bonner said:

I have seen this before, waterproofing causes the rain to run off so it soaks the untreated brickwork below. Treating the whole wall may be the only solution.

 

Do you have a photo of this? Thanks

[Bonner]

35 minutes ago, readiescards said:

 

Do you have a photo of this? Thanks

Not sure, it was in an old house about 12 years ago. I will have a look later.

[PeterW]

2 hours ago, readiescards said:

I will try to create a diagram from my understanding of what there is

the only way you will find this is physical investigation. You’ll need to access the inside of the chimney and get a camera in there and then work out where the water is getting in. As a minimum I expect those pots and the top flaunching needs removing and redoing, the lead work may also be suspect so it will require a good amount of investigation to find the true source of the leaks. 

[readiescards]

On 08/01/2021 at 09:00, PeterW said:

the only way you will find this is physical investigation. You’ll need to access the inside of the chimney and get a camera in there and then work out where the water is getting in. As a minimum I expect those pots and the top flaunching needs removing and redoing, the lead work may also be suspect so it will require a good amount of investigation to find the true source of the leaks. 

 

Well finally done this.  Removed the steel plate sealing the flu to the stack to find all the vermiculite behind was completely soaked.  The strange V pattern on the outside of the gable end exactly matching the distribution of the wet vermiculite (it was basically keeping the bricks wet).  Removed all that to find water dripping in from the lead tray to flu joint.  I collected around 3 litres in the last 24 hours (and it was only raining for a few hours).

 

So I can understand making the flu to lead tray joint can be tricky to obtain a 100% long life water proof joint and the odd drip might get through, what I can't understand is why there is multiple litres of water in the void above the lead tray and underside of the sealed pots.  Going to need the stack above the lead rebuilding I fear

 

 

 

 

 

 

[PeterW]

1 hour ago, readiescards said:

I can understand making the flu to lead tray joint can be tricky to obtain a 100% long life water proof joint and the odd drip might get through, what I can't understand is why there is multiple litres of water in the void above the lead tray and underside of the sealed pots.  Going to need the stack above the lead rebuilding I fear

Glad you have found the issue. 
 

The flaunch is porous and will let water through, it is why there has to be a continuous lead tray with adequate weep vents and it sounds like the tray does not have this. 
 

Also worth checking the lead tray is continuous. I’ve seen them made of multiple sheets with a bit of leadmate between the lap joints and that is a guaranteed leak spot. You have to use a single sheet for the tray - expensive but worth it unless you can find someone who can lead weld and put the correct upstands in for each cavity. 
 

Also, you say the tray to flue joint is leaking ..?? What joint is this, and what flue or flue liner are they using ..?? Photo would be helpful. 

[joe90]

Glad you found the problem, with my stack I read up about it first and learnt about the whole sheet of lead as @PeterW says above, luckily my brickie had been trained old school and was going to do it anyway ?

[Dave Jones]

Looks to me like that sealed stack cant breath at all. 

 

Normal chimney build is pumace liner with every join sealed with the proper sealant then the void between the liner and brickwork filled with vermiculite. This is sealed at bottom and the top of the chimney with blocks, brick, tile etc DPC over the top then a very hard mix made with grano dust to seal it round the pot. Water should never get into this insulated void as its sealed and doesn't need venting.

 

Yes water will get into the chimney but that doesn't matter its fully vented by virtue of the pot and fireplace!

 

Your situation I would start by adding a tray for the chimney to sit on with weep holes to drain it. Take the top off and do it again with a DPC and grano and put some brick vents in it to vent the void, do the same in the attic more brick vents. Even if it was letting in rain water which has no where to go as there is no tray, I would bet it would fill with condensation much like a wrongly fitted warm roof. 

 

It means taking down the chimney but not the end of the world.

 

[PeterW]

47 minutes ago, Dave Jones said:

Looks to me like that sealed stack cant breath at all. 

 

Normal chimney build is pumace liner with every join sealed with the proper sealant then the void between the liner and brickwork filled with vermiculite. This is sealed at bottom and the top of the chimney with blocks, brick, tile etc DPC over the top then a very hard mix made with grano dust to seal it round the pot. Water should never get into this insulated void as its sealed and doesn't need venting.

 

Yes water will get into the chimney but that doesn't matter its fully vented by virtue of the pot and fireplace!

 

Your situation I would start by adding a tray for the chimney to sit on with weep holes to drain it. Take the top off and do it again with a DPC and grano and put some brick vents in it to vent the void, do the same in the attic more brick vents. Even if it was letting in rain water which has no where to go as there is no tray, I would bet it would fill with condensation much like a wrongly fitted warm roof. 

 

It means taking down the chimney but not the end of the world.

 

 

 

Not necessarily - if you look back this isn't a full 4 pot stack and 3 are sealed dummies. One is a vent but can't allow water in as it isn't that sort of flue. There is already a lead tray in place but it looks like its not installed correctly and there are no weep vents or they are blocked. Brick vents in this sort of chimney are not recommended as this should be a sealed void which it clearly isn't..!

 

 

[Dave Jones]

9 minutes ago, PeterW said:

 

 

Not necessarily - if you look back this isn't a full 4 pot stack and 3 are sealed dummies. One is a vent but can't allow water in as it isn't that sort of flue. There is already a lead tray in place but it looks like its not installed correctly and there are no weep vents or they are blocked. Brick vents in this sort of chimney are not recommended as this should be a sealed void which it clearly isn't..!

 

 

 

Just goes to show its the smallest of errors that can cause major problems. 

[readiescards]

Correct: 3 pots are sealed with a fibre glass cap (assuming the cap is still there), they sit on a recessed paving slab (I think).  The live pot has a flexible tube sealed to its upper lip, the live pot sits on some slate supports.  The whole lot is then flaunched (to secure the pots I assume). There are no weep holes in the flaunch.

Under the flaunch is a large single brick void.

11 brick rows down from the top is a single solid sheet of lead, with tiny weap holes (I've never been able to confirm if water comes out of them - and looking just now while the dripping is happening inside I can see no evidence of water running out)

The builder cut a square hole in this sheet and pushed the flap down(!) so the log burner installers could run the log burner flexy flue up to the live pot.

This hole was then sealed up from below, it was later also further sealed up from above.

This seal is currently dripping.

 

It is dripping because a considerable amount of water is getting into the stack void above the lead - currently the drip is 5 litres in last 24 hours so gawd knows how much water is sitting in the void.  Many of the bricks above the lead tray have green mould growing up them now from being constantly damp.

 

The builder says not his fault.

 

Questions:

1. how many litres of rain water should a void be expected to capture in a normal storm?  A few cc? Less than 1 litre?  More than 5litres? (I personally assumed practically nil)

2. should I be able to see evidence of water coming out of the weap holes (e.g. after 3 years maybe staining on the lead) as I can't 

3. should an air-brick be installed in this cold void (it was originally filled with vermiculite but this got wet from poor chimny pot sealing so was removed)

4. would the lead sheeting sag under its own weight so directing the collected water to the centre (and therefore around the flue)?  (from below I can not see evidence of sagging but only needs to be a few millimetre to create an issue)

 

Thanks all

 

[dpmiller]

shouldn't an upstand have been formed in the lead around the hole for the flexi?

[readiescards]

14 minutes ago, dpmiller said:

shouldn't an upstand have been formed in the lead around the hole for the flexi?

 

Yep I think so, pushing the cut flap down seems to be the worse option available!

[PeterW]

1 hour ago, readiescards said:

Questions:

1. how many litres of rain water should a void be expected to capture in a normal storm?  A few cc? Less than 1 litre?  More than 5litres? (I personally assumed practically nil)

2. should I be able to see evidence of water coming out of the weap holes (e.g. after 3 years maybe staining on the lead) as I can't 

3. should an air-brick be installed in this cold void (it was originally filled with vermiculite but this got wet from poor chimny pot sealing so was removed)

4. would the lead sheeting sag under its own weight so directing the collected water to the centre (and therefore around the flue)?  (from below I can not see evidence of sagging but only needs to be a few millimetre to create an issue)

 

Thanks all

in order :

 

1. None of a tiny amount if sealed correctly. 
 

2. Yes If they have been done correctly but I suggest these haven’t. 
 

3. No no no no no, absolutely not !!! That void must be full of vermiculite as should the remainder of the flue to insulate the liner. 
 

4. Possibly with the heat of the liner but it really should have been sat on a full liner of vermiculite so should have nowhere to go. 
 

30 minutes ago, dpmiller said:

shouldn't an upstand have been formed in the lead around the hole for the flexi?

 

I am not sure that setup as it stands meets the Hetas or BRegs but could be wrong. It should have a top hat type setup but I would not expect it to be diverting any water of volume as the liner should be hung off a pot liner and they have a proper shroud to go over the top of the pot. 
 

I think water is getting in via those other pots, and you will need to somehow create a secondary void which is fully sealed. If it was me, that lot would come down and a new stack built with a single compartment for the flue that is properly insulated and a lead tray below the pot to catch any leakage, then a full lead tray further down for the “fake pots” that is open. This would mean the flue can be correctly installed and the void cannot retain water. 

[readiescards]

(The East stack has the log burner flue)

Today the We st stack soaking of the gable end bricks has now got so far it has breached into the living space both in the attic and in the utility room (the one below the red tiles):

 

You can see the bricks above the lead tray on the West stack are very very damp to the point mould is growing in the mortar.  Below the lead tray is a patch of brickwork that has been repointed and had a water proofing applied (which has run down the wall creating the horrible looking square patch).  The soaked bricks are now onto the utility wall

 

I think considerable water is being captured in the 'sealed' void above the lead tray of West stack (which I believe is an empty single brick wall void) that is some how breaching the lead tray and various cavity trays below that.  

 

Question:

* I've been told the flaunching is absorbing rain - is there a good reason for the flaunching not being regular water proof concrete?

* discussion above suggest this void should be ether double skinned/insulated.  Rather than using vermiculite (which once damp collapses and is damp for ever) could it be filled with  rigid insulation (Xtratherm type stuff) - would that be a 50+ year solution?

 

Thanks as always - the Buildhub continues to be a life-saver for me

 

[markc]

This seems odd, a chimney pot isnt a big hole/funnel to collect so much rain water. 

[readiescards]

Looking up from the attic into the live stack at the underside of the lead I can see drips of black sealant (I guess). 

 

Is it normal practice to apply sealant to the brick-lead joint?

 

thanks