Damp Issues - What's the cause?

veedee · 25 Nov 2020

I need some advise on the cause and remedy of some damp issues in this Victorian property

Picture 1 - Damp which starts from the floor and appears to rise.

Picture 2. External wall directly behind damp in picture 1

Picture 3 - Internal party wall on upper floor

Picture 4 - External picture of area affecting picture 3

Property appears to have a new roof, which was installed prior to occupation by myself. The loft has zero insulation

skhudy · 25 Nov 2020

Downstairs Damp - I'd guess the damp course is beneath the air brick. As with so many older houses when work is done outside by inexperienced builders they keep making the ground level higher with no consideration to the damp problems which will come a few months later. The outside levels should be a few inches below the bottom of the air brick, but its not, so looks looks to be breached. To make matters worse some cowboy had cemented along the bottom of the wall well above the damp course to stop damp - i think it will actually aid its passage up the wall, the effects you are seeing inside. I suppose the only positive is they didnt concrete over the air brick

What you need, if you don't want to have it all dug up outside and lower the level of it all, is have that render taken off the bottom. Then have a channel dug 4-5" distance from the wall, perhaps all the way round that side of the house if its at that level, at least 6" down and fill with shingles / stones.

Then inside you will have to have the damp plaster hacked off up to 1m or so and re-plaster as its probably blown (sound hollow when tapped?). Its going to take some time to dry out (months) once the work outside is done.

upstairs is water ingress from a leak from the tiles (unlikely as it looks reroofed? note it looks like it is dipping on the side of the leak - weight from the concrete tiles, and no extra support) or from the part wall which is more likely. You will have to have someone go up and look at the pointing on the party wall, it looks like someone has had a go patching things up already

tel765 · 25 Nov 2020

You appear to have a solid wall, is that the gable wall?
An air brick suggests that the floor is suspended - how many air bricks can you see around the house?
The sand and cement plinth should be removed and all your pointing repointed in lime mortar.

The interior recess seems to have rising and penetrating damp - hack off all traces of damp plaster in the recess on the return wall and the chimney breast. And render with a 3:1 sand & lime mix.
Some form of bitumen tanking has previously been tried - it failed.
Do you intend to keep the tiled fireplace?
Has the flue been swept?
Examine closely the c/breast and the other recess for damp signs.
Examine the floor for rot - if it is indeed a suspended floor.

The gutter on the rear elevation is sagging.
The render to the rear elevation is not of a high standard.
The flat roof flashing - is it lead or felt? Any damp below?

Both the chimney stack and the parapet show fillets of sand and cement " flashings" instead of lead flashing - the front apron lead flashing on the stack is hanging loose. The fillets might crack and allow leaks.
The stack has a slight inwards lean.

The render on the parapet has been repaired?
The last flat bit of the parapet capping should be sloping to discharge water - instead its ponding.
This is probably the cause of the damage below on the party wall etc.
The neighbour's parapet shows an air brick in an unusual hump - is there/ was there a chimney breast going up in that corner of the neighbour's house?

mrrusty · 27 Nov 2020

all your pointing repointed in lime mortar.

Forget this. If it's cement pointed you haven't a hope of getting it out nicely.

The cement along the bottom of the wall has probably been done because the bricks are spalled below. If you take it off also plan to renew the brick courses.

I am fairly confident that it won't be "rising damp". I am of the group who think it mostly doesn't exist, and my restoration of a 1902 house and what I have seen with my own eyes, has not changed my thinking. I agree with https://www.heritage-house.org/damp-and-condensation/managing-damp-in-old-buildings.html

IMHO that is all condensation. Lower areas of solid walls are cold, and will attract condensation. The other damp I agree may well be coming from the parapet wall.

veedee · 27 Nov 2020

You guys are absolutely amazing. Thank you for the responses/advice

veedee · 27 Nov 2020

@tel765 I have responded to your queries in red

tel765 said:
You appear to have a solid wall, is that the gable wall? Yes that is the gable wall
An air brick suggests that the floor is suspended - how many air bricks can you see around the house? three on the gable end, one on the rear elevation and one on front elevation
The sand and cement plinth should be removed and all your pointing repointed in lime mortar. Thanks. Will do

The interior recess seems to have rising and penetrating damp - hack off all traces of damp plaster in the recess on the return wall and the chimney breast. And render with a 3:1 sand & lime mix.
Some form of bitumen tanking has previously been tried - it failed.
Do you intend to keep the tiled fireplace? I actually want to get rid of the chimney and the chimney breast in its entirety.
Has the flue been swept? I am unsure at present. I will find out
Examine closely the c/breast and the other recess for damp signs. The chimney breast appears to be damp free on ground floor
Examine the floor for rot - if it is indeed a suspended floor. Floor boards have been lifted and there is no rotting to the joist on the ground floor

The gutter on the rear elevation is sagging. Great spot. That is disappointing as i understand that the roof/gutter & render was done approx 1-2 years ago
The render to the rear elevation is not of a high standard. You're right but what gave this away? What are the signs of poor quality render?
The flat roof flashing - is it lead or felt? Any damp below? It is lead

Both the chimney stack and the parapet show fillets of sand and cement " flashings" instead of lead flashing - the front apron lead flashing on the stack is hanging loose. The fillets might crack and allow leaks.
The stack has a slight inwards lean. As the chimney is not in use and due to all its defects, I would like to remove this and the chimney breast. Is this a job for a competent diy'er?

The render on the parapet has been repaired? I am confident work was done to it, but this was before i took ownership
The last flat bit of the parapet capping should be sloping to discharge water - instead its ponding.
This is probably the cause of the damage below on the party wall etc.
The neighbour's parapet shows an air brick in an unusual hump - is there/ was there a chimney breast going up in that corner of the neighbour's house?I do not believe so. I have attached an pic of the neighbours roof

veedee · 27 Nov 2020

mrrusty said:
Forget this. If it's cement pointed you haven't a hope of getting it out nicely.

The cement along the bottom of the wall has probably been done because the bricks are spalled below. If you take it off also plan to renew the brick courses.

I am fairly confident that it won't be "rising damp". I am of the group who think it mostly doesn't exist, and my restoration of a 1902 house and what I have seen with my own eyes, has not changed my thinking. I agree with https://www.heritage-house.org/damp-and-condensation/managing-damp-in-old-buildings.html

IMHO that is all condensation. Lower areas of solid walls are cold, and will attract condensation. The other damp I agree may well be coming from the parapet wall.

Repairing spalled bricks sound like it could be costly. I hope they are not spalled.

There has been no heat to the property in approximately 1 year. Do you believe that this could still be condensation?

skhudy said:
Downstairs Damp - I'd guess the damp course is beneath the air brick. As with so many older houses when work is done outside by inexperienced builders they keep making the ground level higher with no consideration to the damp problems which will come a few months later. The outside levels should be a few inches below the bottom of the air brick, but its not, so looks looks to be breached. To make matters worse some cowboy had cemented along the bottom of the wall well above the damp course to stop damp - i think it will actually aid its passage up the wall, the effects you are seeing inside. I suppose the only positive is they didnt concrete over the air brick

What you need, if you don't want to have it all dug up outside and lower the level of it all, is have that render taken off the bottom. Then have a channel dug 4-5" distance from the wall, perhaps all the way round that side of the house if its at that level, at least 6" down and fill with shingles / stones.

Then inside you will have to have the damp plaster hacked off up to 1m or so and re-plaster as its probably blown (sound hollow when tapped?). Its going to take some time to dry out (months) once the work outside is done.

upstairs is water ingress from a leak from the tiles (unlikely as it looks reroofed? note it looks like it is dipping on the side of the leak - weight from the concrete tiles, and no extra support) or from the part wall which is more likely. You will have to have someone go up and look at the pointing on the party wall, it looks like someone has had a go patching things up already

Great advice thank you

veedee · 27 Nov 2020

Had a damp guy come in to evaluate the job and he recommended the following works

1. Remove internal damp plaster. Then Tank, membrane & replaster wall

2. Re-point external gable wall (with lime)

3. Treat external wall with Thompson sealant

4. Remove plaster from parapet and install lead flashing to prevent damp on party wall

6. Re-point side wall in loft and treat with Thompson sealant

15 year guarantee

Cost - £5500

What are the forums thoughts?

Also added some pics of the loft.. as this this provides an insight into why the roof is sagging

mrrusty · 27 Nov 2020

DO NOT TANK AND SEAL A SOLID WALL!!!

Sorry it's in caps, but you really should not do this. All you do is seal any water vapour in to the wall structure. Read Heritage House and understand what is being said.

Don't spend money on flashings and sealants on that roof - waste of money. it needs to be remade. Obviously what's happened is heavy concrete tiles have been put on a roof that was originally slated and it has sagged. The structure is nowhere near strong enough and has been bodge braced. Start saving to have it taken off and rebuilt.

I don't know if that purlin is original but it is far too small for what is there now.

Notch7 · 27 Nov 2020

veedee said:
Treat external wall with Thompson sealant

That's a DIY option.

Thompson is not a professional damp remedy.
Professional brick sealants contain silane / siloxane not silicone.

I would be concerned you have had a damp guy around that is just touting for work and not a pro.

What materials is he proposing to use to tank the wall?

Your best options are a cavity drain system like Oldroyd or a breathable system like stormdry masonry protection cream.

Have a look at safeguard Europe for gear that pros use.

https://www.safeguardeurope.com/products/cavity-drainage

tel765 · 27 Nov 2020

mrrusty,

"Forget this ... nicely."

You jumble three wrongs in one sentence.

The wall has a few remnants of failing S&C mortar.
The S&C was an attempt to repoint the wall without even raking out the beds & perps.
That wall was built using sand and lime mortar.
The wall in question obviously has S&L beds & perps so why ask: "if its cement pointed"?
Raking out that wall would be a simple, easy process.
Raking out any kind of mortar in a brick wall is a simple, easy process unless the beds are extremely tight.

Retro S&C plinths, such as the OP's, are typically installed as hopeful attempts to prevent interior damp - they dont work, they make things worse.
The OP would begin to see the conditions behind the plinth after removing about 450mm of plinth.

Ref your denial of rising damp - do you also deny capillary action?

jacko555 · 27 Nov 2020

tel765 said:
Ref your denial of rising damp - do you also deny capillary action?

https://www.heritage-house.org/damp-and-condensation/managing-damp-in-old-buildings.html said:
The Ultimate Proof that Rising Damp Doesnt Happen!

Have a look at this photograph I took a while back. Water, running through a millrace - and the wall is dry!!

.. and just to ram the point home - this is the millrace, at an hotel I stayed at. The wall above the water surface is bone dry - that's the restaurant wall you're looking at!. Damp proofing companies tell you water magically 'rises' a metre up the wall - why a metre I wonder? Anyway - this wall is sitting in water 24/7, and its bone dry - so, Mr Rising Damp man - how do you explain this?

JohnD · 27 Nov 2020

tel765 said:
Ref your denial of rising damp - do you also deny capillary action?

Surely you've seen that in good, clean, unplastered brickwork, it can only rise a couple of courses?

Because the pore size in the mortar is not the same as the pore size in the brick. Capillarity easily runs from large pores to small, but is inhibited in running from small pores to large.

A cavity full of builders rubble, or a wall plastered or rendered, enables damp to rise.

In any wall, it will stop at the point where evaporation from the surface equals damp rising from below. A well-ventilated subfloor void is a great help in controlling damp.

Sadly many builders thought that the best way to cure a damp wall was to apply a mortar plinth, sometimes treated with bituminous paint, or to render the inside with a waterproof mix. Not only does this facilitate capillarity, it also prevents evaporation from the surface of the bricks. As does tanking.

tel765 · 27 Nov 2020

vedee,
Removing the chimney breast from the stack down to the ground floor has ben done by DIY'ers but its also a matter of safely making good behind you as you come lower. There's quite a bit of work in it.
Removing the c/breast from one floor only often requires a builder.
A builder's heads up on site would help anyway.

Wherever plaster is removed then dont go back on with gypsum plaster - only use a S&L render.

If the ground floor c/breast is removed then it would be best to remove all plaster from the GF wall, and clean & blind the sooty flue bricks, and then render with a Sand & lime render.

The parapet would be best worked on from both sides but i still cant see if your side has lead flashing or a S&C fillet?
Unless you are going to do a new roof then make all roof remedial repairs as soon as possible - you dont want water entering your house.

The loft pics show what looks like active wood rot (and much harmless white mould). That wood rotted corner with the repaired rafter needs investigating soonest.
The purlin has been repaired/reinforced at either end.

Perhaps get a permanent light in the loft asap.

jacko555 · 27 Nov 2020

I cited the source of the pic in the quote title.

I did not claim to take it.

Odd resposnse there ted/ree/vin/bobasd.

Do you disagree with the quote?

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Damp Issues - What's the cause?

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