Gable Wall Damp Shenanigans

[Alex O]

Okay, let's get to it.

We have a solid gable wall on our 1904 semi-detached. It's double skinned and has been rendered in sand and cement. As you can see from the pics the render doesn't cover the air bricks and there's a French drain at the bottom.



This drain appears to be draining effectively, in that the pea gravel isn't any wetter than you'd expect it to be under the surface layer and I haven't seen any worms or anything that would indicate blockages.

The bricks at the bottom of the exterior side seem to be pointed in some kind of tarry black substance. I assume this is an attempt at damp proofing.

The render is blown in several places, so needs at least a repair job. Inside, the wall is dry except for the bottom couple of feet. I don't know whether the damp at the bottom spreads across the whole wall or just the section where the bricks are exposed in the cupboard under the stairs:



There have obviously been serious damp problems on the ground floor where it meets the gable wall in the past. All the flooring, including the joists, have been replaced along this wall. The plaster has been removed up to about a metre in the under stairs cupboard and there is a clear line where the damp stops a couple of feet above the air bricks. There was evidence of dry rot on the cupboard door frame, so when we bought the place we had an independent damp surveyor look it over. He said the dry rot was old damage and there was no active rot and the wood just needed replacing, which we've now done. His assessment of the damp on the exposed bricks was that it was condensation.

Where there is still plaster and wallpaper on the rest of the gable wall, it feels cold to the touch but we can't see any actual damp patches. There are a few places where it sounds like the plaster is blown so there are repairs to do. Large sections have also had a layer of renovating plaster skim added, presumably as some kind of attempt to damp proof it.

So, my first question for the experienced and expert out there - would you agree with the surveyor's assessment that this damp on the inside is condensation, rather than penetrating or rising (I know rising is now thought to be vanishingly rare)?

We have been ventilating the house as much as possible since we bought it - we removed all the old carpets, laminate etc, have cleared the air bricks and installed a stove which is hopefully circulating the air. When we've looked under the floor in the hallway the movement of cobwebs tells me that air is moving well around the sub floor.

A couple of months ago there was actually beading of water on some the bricks in the under stairs cupboard, which isn't appearing any more - is this a sign that our ventilation is working and the wall is drying out? What sort of signs should we be looking for that it is drying, and how long would it take to dry?

Secondly, where should we go from here in tackling this wall? Here are some of my thoughts:

- rake out the tarry black stuff from the bricks at the bottom of the exterior side of the wall. Re-point with a softer (lime?) mortar.

- is the pea gravel okay in the french drain or should we replace it with a larger sized stone?

- given that there doesn't seem to be penetrating damp on the inside of the wall, should we take the "if it ain't broke" approach to the cement render and patch repair in cement? Or should we have it all taken off and re-render in lime? Or some other solution (all the builders seem fixated on K Rend or similar but I have no idea if this is really suitable. I'm assuming the bricks will be in too much of a state to have the render removed and just repoint them - also we might fall foul of building control and the old 25% change to thermal elements thing.

- Add vents to the door of the under stairs cupboard (at the moment I'm leaving it open a crack). It smells musty in there but I think it's less musty than it was!

- remove the layer of renovating plaster from the interior wall and let it all breathe / patch repair the original plaster (likely to be lime in a house this age?)

Sorry this is such a long post! Hoping for some advice from all you old hands at dealing with damp!

 

[Feltwell]

You've put a lot of stuff there Alex - but a biggie that you haven't mentioned is how the exterior ground levels relate to the interior floor levels, and to the damp proof course (at 1904 you will almost certainly have one, probably in slate). If it's not obvious then it should be below the bottom of your floor joists - the top level of the airbricks is a good starting point. Are you sure that's a French drain, and not just a slot filled with gravel?

Your damp surveyor scores a big plus for not trying to flog you an injected DPC and all the usual horrors!

You've not been in the place too long have you? Bear in mind that it takes a long time to dry a house out - sounds like you're doing all the right things - but you're talking many months to properly dry a damp house out, not weeks, and I'd live there over the summer first.

The pointing in your exposed brickwork is clearly poor, but that may be under your DPC anyway, looking at your airbrick height.

Condensation is a distinct possibility. Ventilation will help. You don't have to cut holes in the cupboard door for vents, you could start with encouraging air flow around the edges of the door.

 

[Alex O]

The exterior ground levels are below the interior floor levels. I think the DPC is just under the air bricks - I can see blobs of shiny black stuff along that line on the inside, so assumed it is a bitumen felt DPC. What should I be looking for if it's slate?

What exactly is a French drain? I though they were just a slot filled with gravel!

We deliberately went with an independent damp surveyor for that very reason - didn't want to be flogged expensive dry rot treatments etc. Cutting vents in the cupboard door wouldn't be an issue, as the door is new (the old one had rot damage as well so we replaced it).

It's fine for it to take months to dry out, we're not in a rush and want to get that wall right - but what are the signs that it's drying out? I just don't want to miss something obvious that we should do now to get it sorted.

In the end, if it is condensation, won't the bottom of that wall always suffer to some extent, with it being the coldest part of the house? Is it just a matter of mitigating the problem as much as possible with ventilation?

 

[Feltwell]

Bit of a rushed reply, will look properly later:-

A French drain has a means of taking the water away at the bottom of the trench, to your drain or a soakaway - usually a perforated pipe. However don't worry too much about this for now, start with the simple things. Dig some gravel out after a wet period and see if the trench is holding water, if it isn't then don't worry about it. You only really need a pipe if the water won't soak away naturally, for example on heavy clay soils.

If the DPC is at the bottom of the airbrick, the gravel is too close to it - splashback from water falling onto the gravel could be going back onto the bricks above the DPC. From memory 3 courses of brick is the recommended separation from ground level to DPC - take some gravel out. Shiny back stuff does indeed sound like a tar DPC, a good sign. Is it possible to space those slabs a bit further away from the wall? They are a bit close - not critically so but personally I'd be happier if that gravel trench was a bit wider.

Looking up, is there guttering above and is it in good nick? What about the downpipes? Get out there when it's chucking it down with rain, easiest way to check for leaky joints even if your neighbours will think you've lost the plot! Don't forget cast iron can look good on the front and be rotten as a pear at the back, where no one ever paints it.

Signs of drying out - colour change on the bricks, white deposits on the bricks as the salts are left behind as the water evaporates off.

Yes, condensation hard to cure, ventilation will definitely help. The pointing on that exterior brickwork really needs redoing as well, but as a quick & easy first step get some gravel out of that trench and check rainwater goods would be my advice, along with ventilating the cupboard.

It'll be a long slow process of trial and error I'm afraid - often is for causes of damp - lots of "it could be this".

 

[Alex O]

The trench is in a shared ginnel and the slabs are only really wide enough to get the bins down, so I don't think widening the trench will be an option. We could certainly take the gravel out and put a grille over though.

Guttering's all fine and that cast iron pipe is the soil pipe. The plastic downpipe seems to be okay but I'll check again when it's raining hard (though it backs onto the porch, not the inside of the house anyway).

Thanks for the advice - will keep at it! Could be a lot worse I s'pose (and certainly has been in the past).

What are your thoughts on repairing / replacing the render? It needs attention but I don't want to replace with lime for the sake of it when there doesn't seem to be any water penetrating at the moment. Am I right in thinking we'd have lime mortar and lime plaster in a house this age? I know cement was around then but I don't know how widely it was used.

 

[Feltwell]

Looking again at your picture - a significant clue of what the problem was - look at the paint line on the bottom of that soil pipe, the old ground level was clearly at or slightly above the DPC, which could easily lead to the bottom of the wall becoming saturated. I suspect a previous owner has moved slabs away or hacked concrete out and put that gravel in as part of their fix. I'd still lower the gravel though. Even a grille will cause some splashback.

Render - a huge amount of work to remove cement-based render and impermeable finishes, quite possibly for no benefit, esp. as you say there's no penetrating damp. I'd do local repairs only for now. May well not be causing any problems. Could have been lime or cement originally, you're in the changeover period.

Are the bottoms of your joists all above the DPC level? They should be.

How would your neighbour feel about a wider, lower, all gravel path? It's an option. If you wanted to stop the gravel moving about too much as you wheeled the bins over it you could always use some groundguard tiles filled with gravel.

http://www.toolstation.com/shop/Landscaping/d130/Ground+Control/sd3225/Ground+Guard/p94411

 

[Alex O]

The fix was actually done professionally about 16 years ago - we have the details in the house paperwork. Flooring was replaced in the hallway and room behind (with undersized joists, which we'll have to replace as we want to tile those floors), render repaired on the gable wall and the trench dug and filled with gravel. On the paperwork it says this was to deal with woodworm, though whether it was really rot I don't know. Certainly there is evidence of rot in the cupboard and staircase.

Thing is, because the wheelie bins take up a lot of space in the ginnel, we need to be able to walk over that gravel, so it'll need some sort of cover if we take the stones out. Otherwise I'll break my ankles pushing my bike up there in the dark after work! Our neighbour is very elderly too so we need to make it safe.

Yes all joists are above DPC - they meet the top of the air brick course.

So patch repair the render in sand and cement again? Or some other material?

 

[Feltwell]

Use sand & cement - and I'd use PVA to bond it onto the wall - no point in using anything else really, when everything around it is impermeable anyway. Only thing is, no matter what you do, a patch repair will always be visible - always a downside with render. Personally though, unless a lot of the render was shot, I'd patch repair it to a finish as good as you can possibly get, paint the whole wall and live with it - especially on the side of the house.

Re. ground levels - there's always a compromise, and it *may* be that the work done 16 years ago cured the problem - 3 courses of clearance is desirable but it is at least clear as it is now - so you could ignore it for now and see what happens. Or, to make sure it's not a cause and if keeping the full width of the ginnel paved is a must have, you could either go for ground guard tiles and gravel as I put above, or of course re-lay the existing slabs lower down - in fact go low enough and you can hard pave right up to your wall if you really wanted to, personally I'd keep a bit of gravel up against the wall all the same.

"Woodworm" is a bit of a catch all term for a variety of wood munching wee beasties, but all generally need the wood to be moist, and making it dry breaks the lifecycle. All the nasty chemicals that get used aren't really needed if you can get the wood dry.

Adding a grille will be trickier & more work than you think I suspect. Have a look for old posts on here by "Zebra", she had a bit of a nightmare with this on the back her house from what I remember - it backs onto a churchyard, she needed to lower the ground level but couldn't have an open trench, a grille went in but it was lots of work if I remember rightly.

I hope all this is of some help. I don't profess to be an expert on damp or old houses.

 

[Alex O]

This is all very helpful, thanks so much.

I like the idea of lowering the whole ginnel pathway and making it a gravel surface. We're having a small extension done in the Spring which I need to talk to the neighbour about, so we can add this to the list of inconveniences we'll be putting him through (still, hopefully he'll be keen if we're paying - his wall doesn't look too healthy at the bottom either).

Not fussed about the patch repairs and the look of the wall - you can't really see it unless you're in the ginnel anyway, so we don't really care how it looks, as long as it's keeping the rain out. What sort of paint is best? It's not painted at all at the moment.

 

[Feltwell]

Over sand & cement, you may as well use a modern masonry paint.

I've been using some Bedec paint recently, following a tip on here - very impressed with them and the quality of their products - they do a masonry paint, though I haven't used it. Only a small firm so don't expect flash marketing, but they do seem to know their water-based paint technology.

http://bedec.co.uk/extraflex leaflet.pdf

I've used Sandtex years ago, who are probably the most widely known, and wasn't that impressed.

 

[Feltwell]

By the way - not sure if you're aware, but your existing render looks like it's "Tyrolean" over a smooth base coat to me - it's a wet mix that's flung on with a special gun. You really won't be able to match it in without hiring a gun and using the right mix, but it's not that hard to master. Use Google images and see if you agree that it's the same finish.

But if you're getting an extension built, why not use the same finish on that, wait to do your gable wall until then and get the builder to do it then? I'm presuming you're getting a builder in and not DIY-ing your extension. If you do the prep work it will take them minutes to fling some extra Tyrolean mix onto your patches.

 

[Alex O]

Yes that will be the plan - we'll sort this wall out in the Spring when the extension's done. We've already brought it up with the builders we've been asking to quote, but each of them had a different opinion, none of which seemed particularly sensitive to the period of the house or the interior damp, hence I came here for advice.

There's lots of stuff we're happy to DIY, but rendering this wall isn't one of them. We'll do the path ourselves though if the neighbour agrees to the plan. I've shovelled so much gravel in landscaping gardens over the years I could put it on my CV.

 

[88v8]

As regards damp and drying out, scatter a few hygrometers around the house - one in the cupboard - and keep a weekly record of the relative humidity (RH) readings. RH will vary anyway with the seasons - ours is highest in the winter when the stoves aren't in use, but over an extended period it will show a trend, and the individual meters will identify damp rooms.

If you're into spreadsheets, you could do a chart and a Powerpoint presentation when you want to bore someone.
https://www.amazon.co.uk/Outdoor-Thermometer-Hygrometer-Temperature-Humidity/dp/B008M2TGL2/ref=pd_lpo_201_lp_t_4?_encoding=UTF8&psc=1&refRID=7PGS8GW1D0XPD6GFP65K

A little surprised that you have internal damp in a cavity wall, but perhaps it's only cavity from the dpc upwards.

Ivor

 

[Feltwell]

Is it a cavity wall? I'd assumed it was a solid 9" wall, I can't see the brick bond properly in those pictures. At 1904 it could be a cavity wall, but I think solid was still more common then.

If it is a cavity wall and if after a prolonged period of drying out there was still a damp patch I'd be knocking a brick out internally to see if the cavity has got anything bridging it. Endoscope is the best way to look but a mobile phone does a pretty good job if you can get your hand in there!

Hygrometer sounds like a great idea.

 

[Alex O]

It's a solid wall. The front elevation has a finger cavity, but it's otherwise 9" solid walls.

Will look into hygrometers, thanks.

 

[Alex O]

General question:

I've been wondering - if rising damp is a myth / extremely rare, why the need for DPCs?

 

[Feltwell]

My personal view - and potentially only mine! - is that "rising damp" is not a myth, but it gets blamed for a multitude of other things.

A DPC can be slate, tar, felt, plastic (if modern) - or even very dense engineering bricks - all very stable items that do not really degrade, especially when tucked up all nice & safe inside a brick wall. Unless some eejit has physically done something to damage it your 100+ year old DPC will be working as well now as the day when Bert & Alfred put it in.

So picture this:-

House with an external ground level that's too high, it's bridging the DPC, hence the wall is damp. Local "damp proofing specialist" comes in - "Ooo, your DPC has failed causing rising damp, I'll inject your walls with silicone, knock back all the internal plaster to 1m high and stick an impervious render on and give you a lovely certificate to keep your mortgage company happy". He/she (equal opportunities for shysters!) does the work, chances are the damp is not cured but crucially the render hides the problem, so householder thinks all is well. However, they *may* just have cured the problem - either because they've lowered the ground level to inject, or have injected above the original DPC, so above ground level, presuming the injected DPC actually does something.

Chances are it's just hiding the problem and eventually symptoms such as rotten joist ends will reappear.

"Rising damp due to a failed DPC" is an easy one to quote that most householders will find difficult to argue with. More likely is "Rising damp due to a bridged DPC", or it's nothing to do with rising damp at all and is just condensation, or it's failed brickwork /stone pointing, re-pointing in cement, a leaking pipe, dripping gutter, cracked render, internal suspended timber floor replaced with a solid concrete one which pushes the moisture into the walls, etc etc etc. True causes of damp are many and varied but I do believe that if you build a brick wall with no DPC you stand a good chance of getting rising damp, although the effect can be minimised by breathable plasters & pointing giving the moisture an escape route.

"Zebra" on here has done a frankly heroic "1 person with some help sometimes" restoration on a house that was formerly in a very sorry state. If memory serves me right
she ended up cutting a new physical DPC in to her walls - which would be a horrible job - as the house didn't have one and she couldn't stop the damp in the lower part of the walls, despite doing everything to maintain breathability. The DPC fixed the problem. Zebra, if I've remember that incorrectly, feel free to shoot me down in flames! :wink:

 

[Zebra]

"Zebra" on here has done a frankly heroic "1 person with some help sometimes" restoration on a house that was formerly in a very sorry state. If memory serves me right she ended up cutting a new physical DPC in to her walls - which would be a horrible job - as the house didn't have one and she couldn't stop the damp in the lower part of the walls, despite doing everything to maintain breathability. The DPC fixed the problem. Zebra, if I've remember that incorrectly, feel free to shoot me down in flames! :wink:

Thank you Feltwell. My flame gun is out of fuel, so I'll let you off.... Indeed. My house is very old, its bricks are very soft and absorbent, and its rising damp was real. However, I agree with your analysis above. The causes of damp are many and varied, and sometimes simple cures can be found. I mean, not in my case, but sometimes..... I imagine.....

 

[TheRoost]

Your pointing on the lower courses looks just like the lower courses on mine, cement slathered on much wider than the joints, so on the faces of the bricks, and probably not very deep into the joint . It was causing some damp patches on the brick work outside, and where I've removed it and repointed with NHL, the bricks have dried out nicely, only the bricks below ground level are wet now and the lime mortar joint just above ground is dry(yet the dpc is a few courses above that). A good starting point would be to chip out a small area of the bad pointing and see what type of mortar lies beneath it, my bet is that it will be lime.

I also have the same shiny black blobs of DPC visible from the inside, it appears to be bitumen, when I raked out the pointing on the outside wall theres about a 4mm layer of the black stuff with lime mortar on top of it.

Which direction does your gable wall face, does it get much rain, any sun?

 

[Alex O]

The wall faces SSW, and is about 1.5 metres from an identical wall on the neighbour's house, so it doesn't get battered with rain, but not much sun either.