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Damp issues on single skin brick wall

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 pec 25 Jan 2014
I'm renovating a Victorian terraced house at the moment. I've ripped out the kitchen units and stripped the tiles off the walls to find the plaster behind is saturated.
Its had a DPC injected at some point (regular holes drilled in the bottom course of bricks) but has incorrectly been replastered (for a damp wall) with a gypsum based backing plaster which was also down to the ground, thus bridging the DPC. What I also discovered is the outrigger which contains the kitchen and has 3 external walls is built from a single skin of brick. The dampness extends to the ceiling so appears to be penetrating as well as rising, not a surprise given the single skin.
I'm considering how best to remedy this and have come up with the following options:

1) Inject new DPC and replaster with a sand/cement render + waterproof additive.
This would be cheapest and quickest but I don't know how long waterproof additives remain effective and it would offer crap insulation to a room with high condensation levels.

2) Build a second skin inside from lightweight breeze blocks with plasterboard over.
Still cheap, would solve both damp issues and improve the insulation a bit, but I can't afford to lose enough space to leave a big cavity with insulation, just a small cavity (25mm) to stop damp bridging.

3) Build an inner skin from timber studwork with Kingspan between the studs, cover with ply or OSB sheets and plasterboard.
This would solve the damp, greatly improve insulation and the ply sheets will make fixing units to the walls easy but will be the most expensive and probably time consuming.

4) Glue Kingspan (25 or 50mm) to the wall with silicone (just to hold it) then put ply sheets over it fixed to the wall through the Kingspan with window frame fixings like these http://www.toolstation.com/shop/Screws+Fixings/Frame+Fixings/Hammer+Fixing+...
and plasterboard over that.
This would improve the insulation, be quicker than 2 and 3 and cheaper than 3 but is a bit of a wild card. I've never heard of it done and although the Kingspan should stop damp reaching the ply, water might build up behind it.

Bearing in mind this last point, should I put some weep vents in the outer wall if I go for 2 or 3.

Any comments on the above, or alternatives welcome. Thanks.
In reply to pec:

Always great to discuss these problems when it's somebody else's problem - having lived in and done up a cob house sunk into a bank, and this year having to deal with an incorrectly placed dpc in the current house, you have my sympathy.

Almost certainly is penetrating, but a couple of questions: from your run-down, I take it there's no chance of an external skin?; second, do you have any guesstimate for how much of the problem is from poor ventilation and condensation; third, are you going to be living in this, selling or renting out?

Good, cheap, quick. Which two you want has always been the question and always will.

Martin
 blurty 25 Jan 2014
In reply to pec:

Some options/ things to consider:

Hack off & replace finish with renovating plaster

Ventilate

Check gutters, downpipes for leaks

Check external pointing

Check external ground level

Embedded leaking pipework

Increase level of background heat

External rendering

Stud wall with insulation as an internal skin
 Mountain Llama 25 Jan 2014
In reply to pec: I have recently done something similar to option 3 but the walls in question only had rising damp. Our neighbours had gone through several rounds of dpc injection which had not worked in the short term so I built a stud frame from treated timber protected by tough plastic to a height of 1m, just wrapped the plastic around the 2" x 2" battens. I then worked out where the kitchen unit fixings would go and added extra noggins. Insulated with kingspan and then covered with plaster board with the foil membrane. 12 months down the road it's fine and saves the plywood.


OP pec 25 Jan 2014
In reply to maisie:
> (In reply to pec)

> Almost certainly is penetrating,>
Yes, its wet up to ceiling height.

> I take it there's no chance of an external skin? >
No chance! I'm not digging footings for a new wall 2 stories high and extending the roof to cover the extra width etc.

> second, do you have any guesstimate for how much of the problem is from poor ventilation and condensation; >
The walls were tiled floor to ceiling, a pretty effective damp proof barrier and there was an externally vented extractor so I'm pretty sure its a combination of rising and penetrating damp from the single skin.

> are you going to be living in this, selling or renting out? >
Probably selling but possibly renting. I want to renovate it quickly and cheaply for obvious reasons so I don't want grand expensive solutions but I'm not a cowboy so I don't want to just bodge something until I've offloaded it onto some unsuspecting first time buyer.

I've dealt with damp issues before, its the single brick skin on outside walls I've not come across before.

OP pec 25 Jan 2014
In reply to blurty:
> (In reply to pec)

> Hack off & replace finish with renovating plaster >

That's what I normally do but ona single skin wall I'm concerned penetrating damp will always be an issue.

>
> Ventilate
>
> Check gutters, downpipes for leaks
>
> Check external pointing
>
> Check external ground level
>
> Embedded leaking pipework
>
> Increase level of background heat
>
> External rendering
>

None of those is a problem in this case

> Stud wall with insulation as an internal skin >
That's probably my preferred option but its the most time consuming and expensive, though not prohibitive. I just wondered if anybody had first hand experience to pass on on my suggestions or other ideas.

 browndog33 25 Jan 2014
In reply to pec:
I'd personally say studworks internal walls are the quickest and cheapest way of sorting this out.
Mark (20 years construction experience).
Post edited at 18:21
 gethin_allen 25 Jan 2014
In reply to pec:

Surely if the wall is sound and none of the obvious things like gutters, pointing or rendering are shot then it must just be condensation combined with a bridged dpc.
You could use one of the cellotex/kingspan bound plasterboard products but then you may struggle to fix anything to the wall. Battening out the wall first would do the job and you could insulate between the battens and use a moisture resistant plasterboard.
The thing that slightly concerns me is that you say It's a two storey single skin wall?
 browndog33 25 Jan 2014
In reply to pec:
Ps why do you need to ply a studwork wall?
Post edited at 18:23
In reply to pec:

Fair enough! For some reason, I was imagining a single storey extension as you said it was single skin (just out of interest, are we talking single skin as in 4.5", or as in full single-brick at 8" or so?).

I'd personally beef up the water repellency of the brick, dry it out a bit on the inside and go with the kingspan. It's a good solution and not too expensive, depending on the size of room (although still exorbitant for posh polystyrene). I've looked at seconds suppliers in the past, but not found it that marked a difference against friendly local suppliers, and 'unexpected' delays seem to occur with some suppliers.

Bet a bit of ventilation would work wonders, so external vents and an extractor would be worth their cost.

Martin
In reply to pec:
Injection dpcs are a waste of money. I'd go for option 3 with treated timber.
Post edited at 18:54
In reply to pec:

Rising damp does not exist.
OP pec 25 Jan 2014
In reply to gethin_allen

I'd be amazed if condensation could get through floor to ceiling glazed ceramic tiles in sufficient quantity to saturate the plaster. Victorian bricks can be quite soft and absorbant, wind driven rain can soak right through which is presumably why double skin walls and then cavity walls were invented.
Yes its a 2 story single skin 4.5" wall. Structurally that's not a problem, that's all load bearing internal walls are, often to 3 or even 4 stories. I've just never come across it on an external wall because of its lack of weather resistance.

In reply to browndog33

I don't need to ply the studwork but if I do I can easily fix heavy wall units etc to it without having to work out in advance where they will be and preplacing extra studs. I can just screw in anywhere and hit wood. It will also make the wall stronger for tiling onto.

In reply to highclimber

I've seen too many walls with tide marks 2 or 3 feet up them with damp plaster below and dry plaster above to buy into the "rising damp doesn't exist" theory. I know other problems can be misdiagnosed as rising damp but that doesn't mean its a myth. Anyway, its penetrating damp that's my main problem.

In reply to everyone

Thanks for taking the trouble to reply, reading them all helps the "thinking aloud" process. I'm erring towards no.3 What about the weep vents? Its common at the base of cavity walls where damp could track across to the inner skin. They're cheap enough and can't do any harm or can they?


In reply to pec:

Have you thought about tanking the inside of the single skin and maybe treating the outside with a brick veneer?
 mwr72 25 Jan 2014
In reply to pec:

Weep vents are pointless in a single skin wall, they serve no purpose what so ever!
Weep vents sit directly on top of the damp tray which rises 3 course of brick higher on the inner skin than on the outer skin and are mostly used above the lintel on doors and windows.
 browndog33 25 Jan 2014
In reply to pec:
You could just ply/ nog between the studs where the wall units are going to go rather than plying the whole wall. And you don't need ply the wall for additional strength where the wall is being tiled (I've worked on literally on hundreds and hundreds of newbuilds and have never had to ply bathroom studwork etc for that purpose)(just trying to save you unnecessary time, work and money!)
Mark.

Post edited at 23:19
OP pec 26 Jan 2014
In reply to cheek to the rock:
> (In reply to pec)

> Have you thought about tanking the inside of the single skin and maybe treating the outside with a brick veneer? >

I tanked my own cellar with Izonil and its been very successful but the preparation involved is huge and Izonil is really expensive and hard to get a decent flat surface with. Also for the same reason as I've now decided against no.1, it offers next to no insulation so condensation in a kitchen will be a big problem. But thanks anyway.

OP pec 26 Jan 2014
In reply to browndog33:
> (In reply to pec) You could just ply/ nog between the studs where the wall units are going to go rather than plying the whole wall...... >

Yes, that's a thought. I last plywooded a stud wall in a bathroom because I was fixing allsorts to it at different heights, basin, cistern, radiators, cabinets etc and it did make it really quick and easy. But I could just ply (actually I'll use OSB as its a lot cheaper) between worktop and top of wall cabinet height as that's where all the fixing things will be going on.

OP pec 26 Jan 2014
In reply to mwr72:
> (In reply to pec)

> Weep vents are pointless in a single skin wall, they serve no purpose what so ever!
> Weep vents sit directly on top of the damp tray which rises 3 course of brick higher on the inner skin than on the outer skin and are mostly used above the lintel on doors and windows. >

What I was thinking though is that with a stud wall inside the brick with a small cavity, say 25mm, the floor effectively becomes a damp tray. Any water on the inside of the bricks which runs down to floor level will pond up there and weep vents would allow it to escape. Given they only cost pennies and take minutes to install, unless they would actually do any harm I should put them in. Does that sound reasonable?

contrariousjim 26 Jan 2014
In reply to pec:

I feel your pain. I'd create an air gap by adding batons to the damp wall, onto which (not inbetween) I'd add the 50mm kingspan that is fronted by plasterboard as a single unit. This kind of thing:

http://www.building-supplies-online.co.uk/building-materials/plasterboard-p...

We had sodden walls solved this way, the air movement appears to be sufficient (vented under suspended floor) and communicating with roof space also vented through eaves and ridge.
 Ridge 26 Jan 2014
In reply to browndog33:

> I'd personally say studworks internal walls are the quickest and cheapest way of sorting this out.

> Mark (20 years construction experience).

I'd agree with that, and to be fair a bit of studwork, kingspan and plasterboard isn't mega expensive or time consuming in the grand scheme of things. Did a couple of walls in our house, (mixture of cobs, bricks and god-knows-what walls), a couple of years back. Bone dry and significantly warmer.

Ridge (30 years unskilled bodging experience)
 mwr72 26 Jan 2014
In reply to pec:

You can create a damp tray by laying one course of brick then "benching" concrete from the top of the brick down to the bottom of the outer skin where the weep vents will be. You can then sit your stud wall on top of the course of brick, but make sure you wrap the sole plate of your stud wall in a DPC to protect it from any damp.
OP pec 26 Jan 2014
In reply to mwr72:

Yes, I'd been thinking one course of bricks to raise the soleplate out of harm's way might be good idea so I think I'm settled on the stud wall idea now.
Thanks again to all who've replied.
 simonp 26 Jan 2014
In reply to pec:

> In reply to gethin_allen


> Yes its a 2 story single skin 4.5" wall. Structurally that's not a problem, that's all load bearing internal walls are, often to 3 or even 4 stories. I've just never come across it on an external wall because of its lack of weather resistance.

Structurally could well be a problem - internal walls aren't subject to wind loads! Stud framed inner leaf could also strengthen the outer skin, as well as ticking the damp and insulation boxes, so would probably be the best option.
 teflonpete 27 Jan 2014
In reply to pec:

> Yes, I'd been thinking one course of bricks to raise the soleplate out of harm's way might be good idea so I think I'm settled on the stud wall idea now.

> Thanks again to all who've replied.

Use engineering bricks for that floor level course, less absorbant than normal bricks.
 toad 27 Jan 2014
In reply to pec: Hello.

Can I slightly hijack your thread? I have what sounds like identical problems to yours, but I'm not really a builder, so I'm going to need to get someone to sort this for me. The problem is, of course that I haven't a clue what kind of a job I need doing (other than making the damp go away. What do I need? Damp proof specialists, who seem to be riddled with cowboys? plasterer? builder?

(Nottm area if it helps!)

 jkarran 27 Jan 2014
In reply to pec:
Baton with treated timber to create a ventilated cavity then fix foam backed plasterboard sounds like the best bet to me. This job requires building control approval and they may be able to point you in the right direction regarding details around correct vapor-sealing and ventilation to avoid streaming condensation and mould in the cavity. You'll probably need 65 or 70mm of foam to meet the insulation requirements for renovation (0.3W/m2/k). Reducing the penetrating damp from the outside is probably also a good idea, either renew the render or perhaps even just some weather-proof paint.

jk
Post edited at 11:10
 Toerag 27 Jan 2014
In reply to pec:

You can get external insulation slabs which are rendered over these days. The problem with brick walls made with cement is that the cement shrinks in the vertical joints and wind drives rain through the resulting gaps. Fitting any sort of secondary wall inside will still mean you have a damp outer wall which will act as a big evaporation fridge, and any screws holding up studwork will rust. You're better off stopping the brick wall getting wet in the first place by rendering it outside, and even better by insulating it on the outside first. Fitting internal plasterboard walls will make it a nightmare for anyone wanting to hang kitchen cupboards on them. So, render the outside and do what you like inside afterwards .
 another_mark 27 Jan 2014
In reply to Toerag:

Another vote for external insulation.
OP pec 27 Jan 2014
In reply to toad:

Could you give us some details of the problem. Is it also a single skin brick wall or double, solid or cavity, age of house, where on the wall is the damp etc?
OP pec 27 Jan 2014
In reply to Toerag:
> (In reply to pec)

> You can get external insulation slabs which are rendered over these days. The problem with brick walls made with cement is that the cement shrinks in the vertical joints and wind drives rain through the resulting gaps. Fitting any sort of secondary wall inside will still mean you have a damp outer wall which will act as a big evaporation fridge, and any screws holding up studwork will rust. You're better off stopping the brick wall getting wet in the first place by rendering it outside, and even better by insulating it on the outside first. Fitting internal plasterboard walls will make it a nightmare for anyone wanting to hang kitchen cupboards on them. So, render the outside and do what you like inside afterwards . >

The problem with all that is it becomes a massive and expensive job. I'm not cladding 3 sides of the 2 storey outrigger in insulation and then rendering over it as well and then extending the roof to cover the extra width.
As well as destroying the character of the house, rendering can also cause as many problems as it solves. Modern cement is just too hard and brittle for Victorian houses which had no proper foundations and therefore "move" a bit. The render cracks, water gets behind it wetting the wall and then, with a bit of freeze thaw, the render blows pulling half the brick off with it.
The outer skin of bricks is designed to get wet. Modern house have cavities to stop it getting further and Victorian houses were designed to "breathe", using lime plaster inside.
Re the kitchen units, as I've said above, I shall put some OSB over the studwork so I can screw into it anywhere which makes hanging cupboards really easy.

 toad 27 Jan 2014
In reply to pec:

The easy bit is the front wall. The house is turn of the century and has classic black mould problems running up in corners, behind furniture etc. Recent double glazing and new heating are I suspect the root of this problem. upstairs and downstairs all on the front wall.

The problem that's bothering me is the internal dividing wall between the stairs and the living room. The plaster and skirting board has been pushed off the wall at the bottom by serious crystals in the brickwork and the plaster under the stairs (the other side of this wall) is bubbling off.

Any thoughts?

OP pec 27 Jan 2014
In reply to toad:
> (In reply to pec)

> The easy bit is the front wall. The house is turn of the century and has classic black mould problems running up in corners, behind furniture etc. Recent double glazing and new heating are I suspect the root of this problem. upstairs and downstairs all on the front wall.
>
> The problem that's bothering me is the internal dividing wall between the stairs and the living room. The plaster and skirting board has been pushed off the wall at the bottom by serious crystals in the brickwork and the plaster under the stairs (the other side of this wall) is bubbling off.
>


By turn of the century I'm assuming C19th-20th.
Mould suggests lack of ventilation but needs a source of moisture in the air hence is common in bathrooms and kitchens but not elsewhere. From the age it will probably be solid walls so moisture will condense on them but is there a source? Do you dry clothes in these rooms for example?
Heating ought to help, not cause the problem. Have the new windows cured draughts which ironically could have been preventing the mould before? Many windows have trickle vents to help with ventilation.

Re the plaster. Crystals at the bottom of the wall sounds like rising damp. This rarely goes more than about 3 feet up the wall unlike penetrating damp (which it can't be on an internal wall) or condensation which wouldn't produce crystals, these are carried up by the groundwater as it rises.
The normal cure would be to remove the plaster well beyond the visible damage and inject a damp proof course. If its a solid floor as close to the floor as possible, if its floorboards you'd ideally lift them and inject below them. Check there's no rubble below the boards bridging any existing DPC (possibly slate within a mortar course given the age of house).
The wall should be wire brushed to remove old salts and plaster before replastering and brushing on some salt inhibitor wouldn't do any harm. Never replaster previously damp walls with a gypsum based backing plaster (browning, bonding coat or similar). You should use a sand/cement render with waterproof additive or better still a renovating plaster such as Thistle Dri-Coat http://www.british-gypsum.com/products/thistle-dri-coat (click on the first pdf document for useful info) its not easily available in DIY shops but can be ordered from builders merchants like Travis Perkins (about £15 per bag).
When replastering don't plaster down to the floor, leave a couple of inches which will be hidden behind the skirtings and under no circumstances plaster below the new DPC.
As you say, a "damp specialist" should be your man but check what he intends to do. I think there are probably fewer cowboys now than in decades past but there are still some.
Hope this helps. If you want any more advice I'll try but not till tomorrow evening now.
 toad 28 Jan 2014
In reply to pec:

Thanks. I think it's a solid wall. I'm having a log burner installed soon, which I'm hoping might provide some better ventilation and drying, but though it was worth picking the brains of someone who knows. I'm calling a (recommended) damp proof company today about the internal wall. Thanks again
 Toerag 28 Jan 2014
In reply to toad:
Salts on an internal wall is deffo 'rising' damp. All Pec's advice is good, the other 'must do' is to lower the ground levels as rising damp will only rise a certain amount above ground level, so by lowering the level you reduce the height it travels up the walls. Injected DPC grout might help in brick walls but it's useless in rubble walls like mine. Electro-osmotic DPC doesn't work very well either, I have a 'working' system which essentially doesn't. You need to make sure the floor voids are well ventilated to help the walls dry out, and of course lowering the ground level in them will expose more wall from which the damp can evaporate before it gets above floor height and causes trouble . If your walls have damp and your floors aren't sat on DPC then they'll be rotten like mine were. The cowboys that fitted the electric DPC in my house replastered down onto the floorboards (below the DPC) so the ends all rotted off. Salt-resisting cementous plaster seems to keep the salts at bay, but you could also redecorate with Keim silicate paint as that lets the salts through instead of blistering.
Post edited at 13:31
 Toerag 28 Jan 2014
In reply to pec:

>

> The problem with all that is it becomes a massive and expensive job. I'm not cladding 3 sides of the 2 storey outrigger in insulation and then rendering over it as well and then extending the roof to cover the extra width.
Do you need to extend the roof? The stuff they fit over here is only 30-40mm thick.

> As well as destroying the character of the house, rendering can also cause as many problems as it solves. Modern cement is just too hard and brittle for Victorian houses which had no proper foundations and therefore "move" a bit. The render cracks, water gets behind it wetting the wall and then, with a bit of freeze thaw, the render blows pulling half the brick off with it.

Use lime render then.

> The outer skin of bricks is designed to get wet. Modern house have cavities to stop it getting further and Victorian houses were designed to "breathe", using lime plaster inside.

They weren't 'designed' to breathe, they were just built cheaply by people who didn't understand the issues.

> Re the kitchen units, as I've said above, I shall put some OSB over the studwork so I can screw into it anywhere which makes hanging cupboards really easy.

I missed that bit, good plan . You'll lose volume though from having OSB covered in plasterboard though - is there a product that's load-bearing which combines strength with 'decoratability'?
 toad 28 Jan 2014
In reply to Toerag:

Thanks. It's a solid floor, I don't know if that exacerbates the problem or not

On a related note, one company I called to see if they wanted to quote but they wanted an £84 "survey" fee. I didn't go any further with the phone call than that.
Lusk 28 Jan 2014
In reply to Toerag:

- is there a product that's load-bearing which combines strength with 'decoratability'?

Yes, check out Fermacell boards...
http://www.fermacell.co.uk/en/content/walls_ceiling_boards_1222.php

I wouldn't use anything else now (for walls).
Still use plasterboard on ceilings though, because of the weight!
 El Greyo 28 Jan 2014
In reply to pec:

Is the mortar cement, lime or lime with cement pointing? If it's lime with cement pointing then rake out the cement and repoint with lime. It won't completely solve the damp but it does (well, in my experience of one 17th century cottage) help moisture in the wall evaporate and reduce the damp.

As for rising damp, if possible a french drain would help but I appreciate it may not be practical.
 hang_about 28 Jan 2014
In reply to pec:

I had exactly this problem in my kitchen (Sheffield terrace single brick). I'd just had my cellar done and phoned up the same company (not sure they are still in business). They hacked off the plaster and put a studded plastic membrane up against the wall and then plasterboard in front. The idea is to create a small gap between the damp outer wall and the plasterboard. It worked fine for what was a quite extensive problem.
OP pec 28 Jan 2014
In reply to Toerag:
> (In reply to pec)
> Do you need to extend the roof? The stuff they fit over here is only 30-40mm thick.>
The outrigger has a mono pitch roof (front to back), the sides are flush with the walls and would need extending.
I appreciate that external insulation would be an effective solution but its just too big a job, too expensive and time consuming. There's a hell of a lot of other things to do on the house and I'm wanting to get it back on the market by the summer. I just want a reasonably cheap and quick solution that isn't a bodge job.

> Use lime render then. >
If I had to render an old building I'd definitely use lime, but again, there's a huge area to do and I'd need to hire scaffolding and it would take too long and cost too much. Lime is 4 to 5 times the price of cement.

> They weren't 'designed' to breathe, they were just built cheaply by people who didn't understand the issues. >
Can't agree with you on that one. Yes, some Victorian houses were built cheaply (as have some houses in every era including now), but in general they built bloody good houses with the materials available to them. There are hundreds of thousands of them still standing and many will still be there long after more recent houses have gone. A bigger problem is that builders today don't understand how Victorian houses "work" and try to impose modern practice on them.
Sometimes it works but often it doesn't. Huge damage has been done to buildings by repointing in cement for example instead of lime.



 Toerag 30 Jan 2014
In reply to pec:

> The outrigger has a mono pitch roof (front to back), the sides are flush with the walls and would need extending.

Is part of the problem that water is easily able to run down the walls off the sides of the roof due to lack of overhang? We had this with our kitchen 'extension' - the slates finished in line with the wall and had a 'sausage' of cement on them making a crappy parapet down the edge. Water was simply soaking into the sausage and down into the render. We had the edge re-slated with a 50mm overhang which seems to have helped massively and wasn't expensive .
 Toerag 30 Jan 2014
In reply to toad:

> Thanks. It's a solid floor, I don't know if that exacerbates the problem or not

If the house wasn't built like that in the first place then it probably does . As Pec says, many old house problems have been made worse by cement render and concrete floors preventing dampness from evaporating. Have a look on the old building / damp websites for lots of good info and case studies.


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