Damp stone wall dilemma - Differing advice - Please help!

[JONXLR8]

I posted this on the plastering / rendering forum nearly 24 hours ago but have had no response so I guess this forum might be the better place to ask.

This is going to be a bit of a read, bear with me..

Photos:
//www.diynot.com/network/JONXLR8/albums/16326

We are in the process of renovating our front room, originally it was just going to be a new floor and a bit of paint but as usual and especially with old houses (can't grumble it's a lovely house) this has evolved into something a lot more complex.

To give a bit of background, it's an 1897 terrace with solid stone walls and lime plaster, outside is rendered and painted. Last year the neighbours guttering leaked and it took them ages to get the landlord to fix it, which they eventually did. During the time it was leaking it splashed up the outside wall and damp appeared on the wallpaper which has now been completely stripped.

The floor is chipboard layed on to the joists. I intend to rip this up and fit solid oak boards.

To the crux of the matter... the whole room was in lime apart from the area below the windowsill on the front bay and just to either side of it up to about a metre in height which had a thick layer of some sort of slurry, the back layer looked a light grey, then it had a dark grey layer then a skim of gypsum plaster. The lime plaster above these areas was fairly loose for the most part so I decided to remove it along with the slurry / render exposing the stonework. The lime mortar above where the slurry had been was a fairly light colour and looked quite healthy, the area behind where the mortar had been was very dark and damp (you could smell it) and the pieces of wood that had been put in the wall presumably to hold the skirting board on were like sponges, as were what was left of the wooden beads which had partially been removed when they had put this slurry on. The stonework at the front of the bay is also loose in the area directly above the air vent.

This was about 3-4 weeks ago. I've had the dehumidifier on constantly since then and the wall has actually dried out quite a lot. I haven't noticed the mortar going any darker since it's rained heavily today and the wooden pieces in the wall feel more like wood than sponge now.

I've had several plasterers in to have a look and have received a wide variety of advice which has totally confused me. To be clear, the quoted prices included to lift the chipboard floor to allow easy removal afterwards, plastering inside the fireplace and skimming the other walls with lime putty or gypsum skim, and adding some concrete to the bottom of the little drain outside to bring the level up so the water drains straight into the pipe rather than pooling up next to the wall.

Quote 1 - Hack off render outside up to below windowsill and lime render, tank and gypsum plaster inside - Approx £1800

Quote 2 - Fill cracks outside, tank and gypsum plaster inside - Approx £1000

Quote 3 - Fill cracks outside, lime plaster inside - Approx £1400

Quote 4 - Fill cracks outside, lime plaster inside - Approx £700

Only the person doing quote 4 came on recommendation, all others were found online by searching traditional or lime plastering.

A lot of people have said just to tank it or put some sort of slurry back over it but seeing how much water this had built up behind the wall and reading articles like this...

http://www.heritage-house.org/pages/managing-damp-in-old-buildings.html

...has made me think about how the wall needs to breathe and not trap moisture in it. Which is leading me down the lime plastering route but the outside is rendered so how does this effect the whole situation?

We don't plan on moving any time soon so I want to make sure we get it right first time and do it properly.

To add to the confusion slightly, our relatives are offering to help pay for the work which is very nice of them, and naturally they want to make sure we get it done right as well, so on advice from her parents my fiance paid for a damp survey to be done by a local firm, I wasn't here at the time so unfortunately I couldn't ask the surveyor any questions. The result and attached quotation can be found here:

Quote - https://dl.dropboxusercontent.com/u/48985321/letter.doc

Specification - https://dl.dropboxusercontent.com/u/48985321/DPC & Plaster specification.doc

Maybe I do too much reading but wouldn't this DPC injection be a complete waste of time in this type of wall?

Please let me know what route we should take here as we're completely at a loss, thanks. As I say I like the sound of the lime option but I'm no expert and others are suggesting we DPC or tank the wall.

Photos:
//www.diynot.com/network/JONXLR8/albums/16326

 

[Joe Malone]

Jon, I've just posted very detailed responses to a similar problem with granite walls. Can I ask you to read those posts first to see if this clears up any of your questions? If you have anymore questions after reading my last posts then please come back to me.

 

[JONXLR8]

After getting in tonight I've removed the render from the bottom corner of the party wall, the rest of this wall is now only lime. The stonework here isn't as damp as I thought it might be.

Render removed from party wall

• JONXLR8
• 10 May 2013
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I also started removing the render from the reveal, again this isn't mega damp but the wooden insert in there has some drying out to do now it can breathe.

Render removed from reveal

• JONXLR8
• 10 May 2013
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But unfortunately this has resulted in cracks on the render outside so I've put this on hold pending further advice. Should I just remove the rest and repair the outside afterwards, or just leave it where it is?

Cracks appeared on outside render by reveal

• JONXLR8
• 10 May 2013
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[JONXLR8]

Jon, I've just posted very detailed responses to a similar problem with granite walls. Can I ask you to read those posts first to see if this clears up any of your questions? If you have anymore questions after reading my last posts then please come back to me.

Thanks Joe, I'll have a read

 

[JONXLR8]

If you have anymore questions after reading my last posts then please come back to me.

Joe, I've just had a good read of the thread about the house in France, from what I've read would I be correct in thinking the following:

> I shouldn't consider putting anything on the inside walls apart from Lime plaster and a suitably breathable paint

> DPC injection in this case would be money down the drain

If this is the case, the only thing I'm not clear on is what now to do outside. As the outside is rendered, should I fill in the cracks as best as possible and accept the fact that some water is bound to find it's way in, but be comforted by the fact that the lime walls inside will let the moisture evaporate through...

...or...

...hack the render off outside up to a certain level and render with lime and have the best of both worlds? If so, what would you do at the joint between the solid and lime render, surely there would be some movement here due to the differences in the materials.

At the front of the house is a raised concrete section which is below FFL (bottom of the air vent), should I consider cutting a drain into this concrete to guide water away from the wall?

I might lift some of the chipboard by the wall tomorrow and see what condition the joists are in. As can be seen on the photos of underneath the floor there is some rubble (probably the original building material) up against the bay wall so it may be a good opportunity to get rid of this to improve air flow under there.

Thanks for your help.

Under floor looking at bay

• JONXLR8
• 9 May 2013
• 1

 

[Joe Malone]

If you have anymore questions after reading my last posts then please come back to me.

Joe, I've just had a good read of the thread about the house in France, from what I've read would I be correct in thinking the following:

> I shouldn't consider putting anything on the inside walls apart from Lime plaster and a suitably breathable paint

> DPC injection in this case would be money down the drain

If this is the case, the only thing I'm not clear on is what now to do outside. As the outside is rendered, should I fill in the cracks as best as possible and accept the fact that some water is bound to find it's way in, but be comforted by the fact that the lime walls inside will let the moisture evaporate through...

...or...

...hack the render off outside up to a certain level and render with lime and have the best of both worlds? If so, what would you do at the joint between the solid and lime render, surely there would be some movement here due to the differences in the materials.

At the front of the house is a raised concrete section which is below FFL (bottom of the air vent), should I consider cutting a drain into this concrete to guide water away from the wall?

I might lift some of the chipboard by the wall tomorrow and see what condition the joists are in. As can be seen on the photos of underneath the floor there is some rubble (probably the original building material) up against the bay wall so it may be a good opportunity to get rid of this to improve air flow under there.

Thanks for your help.

Under floor looking at bay

• JONXLR8
• 9 May 2013
• 1

Hi Jon,

Firstly, I have read the surveyors report and it is amongst the worst I've ever read. No testing done whatsoever yet he confirms a case of rising damp. It is impossible to diagnose rising damp with a hand held electrical moisture meter. Please read a couple of my articles here on the subject...
http://surveyingproperty.blogspot.c...mp-update-for-2013-part-two.html#.UY30Voy9KSM

What is patently obvious is that the guy who did this survey doesn't even know how to use a moisture meter. He refers to readings of 40% taken in timber as being WME readings. WME stands for wood moisture equivalent and is a term that only applies to readings taken in masonry. These meters are calibrated for use in timber and not masonry so any reading you get in timber is the actual percentage moisture content and not a WME reading. The best thing you can do with this report is to throw it in the bin. Interestingly, BS6576, the code of practice for installing chemical DPC's is notably devoid of any reference to old properties built on the overcoat principle, those using traditional materials. DPC injection is completely inappropriate for your property and would be a complete waste of money.

Every point you make in response to reading the last thread is correct though I do think you should start again with the external render. Hack it off and replace with hydraulic lime. I'm unsure what you mean about the 'joint between solid and lime render'? If two different materials abut then yes, the likelihood is that it will crack due to differential expansion. Ideally you would render the whole elevation or build in a movement joint by leaving a small open joint that you fill with polysulphide mastic or similar.

Internally it sounds like you originally had a waterproof render applied followed by a coat of gypsum. Again, the point here was to dam in the damp rather than allow the wall to breathe and this will store up long terms problems.

How far below below internal FFL is the raised concrete section you mention? Please note my comments with regard to the 200mm required difference in floor heights. That being said you must do something to divert the water away from the wall, this is undoubtedly responsible or at least partially responsible for some of these damp problems. If can't divert into a gully then I'd be considering putting in a soakaway but not sure I'd this is possible for your property.

It's a good idea to remove the rubble but I'm not entirely sure how sub floor ventilation is dealt with, if you have air bricks, how many and where are they in relation to the whole sub floor void?

A few more points I would make... those pipes need properly insulating before you get a pipe burst and whilst on the point of pipe work, when was that incoming water main changed? I'm assuming the copper pipe is the incoming water main because it appears to come through the bay wall, that said, it shouldn't be copper if it is the incoming main. Readings of 40% plus in timber are incredibly high and there's a concern in the back of my mind that you might have a leak, possibly on the incoming main that is contributing to this damp problem. To check this out you will need to do something called a back siphon test. Turn off your external stop cock at the property boundary then place a full glass of water under one of your cold taps. Open up the tap and if the water main is leaking the tap will suck the water from the glass under siphonic action.

 

[JONXLR8]

Thanks again Joe, I knew there was something dogy about that damp survey. Especially from a company which offers to refund the survey fee if you have the incredibly expensive and as you point out, completely useless work done. What surprises me now is how many people have basically told me wrong information, i.e. to block the wall up and let it breathe, is the knowledge about old building techniques really that rare?

My point about the differential between the materials outside is two-fold:

1 - I may not be able to afford to have the whole of the front elevation hacked off and re-rendered in lime, therefore I was thinking along the lines of just hacking off the render under the bay window and having that in lime. I appreciate this isn't as good as doing the whole elevation but is it step in the right direction, if so I can speak to the chap who did quote 4 to ask him to do this and get some of that polysulphide mastic.

2 - Because it's a terraced house, what to do with the wall where it goes on to the neighbours property which is also rendered. Again, from your response I understand the mastic would be the answer.

Re the 200mm:

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Looks like it's barely 200mm from the concrete outside to the top of the chipboard. I hadn't spent too much time examining the render outside but when I moved the stones to take the photo of the vent, there is quite a big gap at the bottom of the vent which must be letting water into the wall. Perhaps this is what is causing the stonework under the floor to be wet and appear to be rising damp?

Re ventilation, there's the vent in the front there and also one in the side passage near the front door / hall. There are gaps in the foundations which must allow air circulation.

Thanks for the tips on the pipework, I'll have a go at that back siphon test.

Under floor looking at bay

• JONXLR8
• 9 May 2013
• 1

 

[JONXLR8]

I haven't done that test yet as we're doing some washing, but I have determined that the pipe coming through the bay is gas not water. Looks like they got a bit heavy handed with the wall when they originally put it in.

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• 11 May 2013
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This pipe goes through to the hatch by the front door:

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• JONXLR8
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This is the gas pipe looking back towards the front room:

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• JONXLR8
• 11 May 2013
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This is the other air vent I mentioned:

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Looking towards back of house:

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• JONXLR8
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This is the water inlet coming in under the front door:

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[Joe Malone]

Jon, a couple of very obvious comments from the last pics you posted. If you look at how much paint and debris has blocked up the air brick you have probably lost half of the cross sectional area for ventilation. This is is significant loss in ventilation so take a blow torch to the vent and burnt off all the paint and clear the vent holes to restore full ventilation.
Secondly, I would take out all the raised gravelled area and reduce that level back to the same level as the path. This will significantly improve wall base ventilation and help prevent future problems with damp.
Thanks for confirmation on the incoming water main and my understanding is that this is close enough to the damp wall to be responsible for the damp conditions if leaking? I still have a problem with it being copper because it appears to be running through lime mortar in places. I'd advise that it needs changing to blue polyethylene pipe. The lime mortar will eat through the copper in a very short space of time but even aggressive soil conditions can eat through the pipe work, hence the need for polyethylene.

Can I just caveat the use of the blow torch, be careful you don't burn timber on the other side of the vent, it you can't get anyone to fire watch at the other side of the vent whilst you do this then try cleaning it with paint stripper and hand tools.

You have posted a pic that shows an air vent in the wall that appears to be above the level of internal floor, you have ran a tape measure in the pic and you can see what appears to be wet chipboard flooring. Is that right because this vent isn't meant to be above the internal FFL, it's meant to be below?

 

[JONXLR8]

Wow, in order to get this done right it looks like there's a lot more involved than I originally thought.

Regarding replacing the water inlet, would that involve digging up the path and the pavement outside where the stop cock is?

Were you referring to the side vent or the front one or both?

As there is a wall to the side and front of the raised area, would this need to be reinforced or rebuilt when the raised area is removed? I suspect it was all built at the same time. Rather than removing it completely would it be worth building some sort of drain into it to guide water away from the wall?

It would also involve a rethink about where this downpipe drains to:

Front of bay 2

• JONXLR8
• 9 May 2013
• 1

At the moment it pools into that little drain then goes into a pipe that exits into the road gutter via a metal section built into the pavement.

What do you think about just lime rendering the bay for now rather than the whole wall?I can see this becoming an impossible job otherwise due to the costs.

It's close but the vent in the bay is definitely below the FFL, just. You can't see it in the photos but when I popped my head below the floor you can clearly see the vent which is clear. I think the reason it looks above is because there was a piece of stone in there that dropped out when I was removing the very well stuck on render, as there's no lintel in there. This is the area of stone work that is loose.

 

[Joe Malone]

Wow, in order to get this done right it looks like there's a lot more involved than I originally thought.

Regarding replacing the water inlet, would that involve digging up the path and the pavement outside where the stop cock is?

Were you referring to the side vent or the front one or both?

As there is a wall to the side and front of the raised area, would this need to be reinforced or rebuilt when the raised area is removed? I suspect it was all built at the same time. Rather than removing it completely would it be worth building some sort of drain into it to guide water away from the wall?

It would also involve a rethink about where this downpipe drains to:

Front of bay 2

• JONXLR8
• 9 May 2013
• 1

At the moment it pools into that little drain then goes into a pipe that exits into the road gutter via a metal section built into the pavement.

What do you think about just lime rendering the bay for now rather than the whole wall?I can see this becoming an impossible job otherwise due to the costs.

It's close but the vent in the bay is definitely below the FFL, just. You can't see it in the photos but when I popped my head below the floor you can clearly see the vent which is clear. I think the reason it looks above is because there was a piece of stone in there that dropped out when I was removing the very well stuck on render, as there's no lintel in there. This is the area of stone work that is loose.

Do the back siphon test first, if it's leaking then immediate replacement required, if it's not then is still definitely needs putting on your to do list. You would of course have to excavate from the house to the main stop cock at the property boundary and replace with polyethylene, but it may be connected o polyethylene at the other side of the wall, the copper running through the wall and the connection would still be vulnerable and prone to leakage.
Just rendering the bay should be fine for now but I still think that the raised ground level is a major issue.
Any vent that is partially blocked needs clearing.
The garden wall is another major issue that will cause penetrating damp to the interior. Is there a vertical DPC between this wall and the front wall of the property? If not then another cause of penetrating damp.
Sorry Jon, I appear to be finding more problems than I'm solving.

 

[JONXLR8]

The garden wall is another major issue that will cause penetrating damp to the interior. Is there a vertical DPC between this wall and the front wall of the property? If not then another cause of penetrating damp.
Sorry Jon, I appear to be finding more problems than I'm solving.

I really appreciate your advice, you seem to be making the most sense out of everyone I've spoken to, after reading a few articles I was sure that ventilation was the important key so I'm glad to have some agree with me that the problem shouldn't be hidden away with tanking solution or whatever.

No idea if there is a DPC on the garden party wall, I suspect not. I know the front wall is made out of some sort of concrete block as the render was put on after the gate post which has since come off.

It doesn't help that the raised section on the neighbours property is higher than ours as our part of the road is on a slight hill, which again means that water is going to flow towards our property.

Do you do any work down in Devon?

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• JONXLR8
• 11 May 2013
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[Joe Malone]

You have two options when dealing with damp, affect a cure or put a management solution in place. Tanking, DPC injection etc are pure management solutions designed to hide or dam in the damp. In the case of DPC injection I would question it's effectiveness anyway, it's the renovating plaster that gives you the appearance of a dry wall but in actual fact the wall is still damp. Your primary approach should lays be to treat the problem at source using minor building works.

Your location means that you have got some difficult management issues but the dividing all should keep water on the neighbouring side. Direct abutment of the garden wall will cause damp problems though.

You need to satisfy yourself that the water from the down pipe is being diverted away from the property. I suspect you have a combined drainage system and the gulley should run to a storm drain but check that gravel isn't being used as a giant soakaway. Of it is then its far too close to the property and is contributing to the wall damp.

Bit far for me Devon Jon.

 

[Graeme1983]

is the knowledge about old building techniques really that rare?

It seems to be sadly. Im in a stone cottage with earth render and some earth bricks and was recomended by a few people to do a DPC or undercut the house. A mate who is a builder mostly of modern passive type well insulated houses was also going to do a full modernised number on the place, going over cement render and concrete with more of the same.

Luckily, sort of, since buying the house and moving close to a different city Ive been in and out of work so couldnt secure funds for the above and in the meantime read up about and researched the wonderful world of lime, clay and ventilation.

For me some good food for thought is these books:

http://www.amazon.co.uk/Old-House-H...1368287023&sr=8-1&keywords=old+house+handbook
http://www.amazon.co.uk/Using-Natur...d=1368286987&sr=8-6&keywords=lime+in+building

Probably the best one for a fiver:

http://www.amazon.co.uk/Lime-Buildi...d=1368286985&sr=8-1&keywords=lime+in+building

Ive been floating on a few different forums to get info on lime and old houses and have to say that Joe here has been one of the most informed Ive came across.

 

[JONXLR8]

You need to satisfy yourself that the water from the down pipe is being diverted away from the property. I suspect you have a combined drainage system and the gulley should run to a storm drain but check that gravel isn't being used as a giant soakaway. Of it is then its far too close to the property and is contributing to the wall damp.

Round the back of the property in the alleyway is a drain. As far as I know the downpipe you can see in my photo literally just goes into the pipe and out through the metal strip on the pavement into the road, although I haven't put any coloured water or anything to prove that yet. You can actually see the metal strip on the pavement in that Streetview image I posted before.

I've left a message for my plasterer to go through what I've learnt here, not sure how much he gets involved in building work but I think the removal of the raised concrete section could be quite involved. I had a quick look at the side of the raised section when I left for work this morning and it appears that it's halfway under the front wall, I'll need to have a proper look but I really don't want to start demolishing the garden wall. Maybe some sort of gutter near the wall of the house could be a sensible if not ultimately the most ideal solution?

As I posted before there is a crack where the render meets the concrete section so I suspect this is on the main entry points water is getting into the wall. What if we put a cement fillet at this point to direct water away that had got onto the wall then dug a trench or french drain to direct it off? Or should I chip off the render and re-render just the bay in lime that we discussed before? Not sure which is best.

Thanks both for your help anyway, I'm glad my curiosity got the better of me and I decided to do some research. Imagine how many people would have just paid the £3k and refilled the wall back up with water.