Old stone house with no foundations. Internal ( breeze block size) white plaster block walls, damp and stained advice on how to decorate please?
Welcome here ..aS a newbie they have made me welcome . So solutions .. there are those blocking paint treatments so an undercoat of that and hen painting with an emulsion type ..breathable will be a method . If the wall plaster is a bit iffy and friable I used a method which seemed common 25 years ago ..I hAVE not looked recently but there is a wall covering in a fibreglass mesh or weave which holds evering together and it is pasted on and then painted over. It wasn’t expensive a totally fireproof ..although a vinyl paint might not
Or ignore the problem totally and glue or otherwise attach vinyl panelling floor to ceiling .. You will see the product ranges in any large Brico. The panels can be 2.8 metres tall and about 30 cm wide and an entire room can be done in a few hours using only a box cutters and a staples or nail punch
Thanks Dan1 I need to do more research because it seems that lime paint isn’t the answer and the panels you suggest are not really the look for an old French stone tbh.
There’s damp, and there’s damp. If this is just a question of poor ventilation then sort the ventilation and you can decorate how you like. Personally I would skim with a thin layer of chaux.
But if a serious damp problem then whatever you do is likely to be very shortlived,
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I am confused on what type of internal walls you have .. your first post indicated that the internal walls which are damp are plaster block … . .Again years ago when I was looking at things there were blocks made of pure plaster and internal walls could be put up very quickly . The alternative in France is to put up a lightweight metal frame work and attach a plasterboard panel on either side and skim coast them and paint. .
Hello Squirrel and welcome to the forum.
Some additional information would be helpful.
When you say " white plaster block walls," do you mean Thermalite blocks known as Beton Cellulaire in France ?
Secondly, is this internal wall standing on the floor, or does it go down below floor level to the ground ?
Thirdly, is the damp staining at the top, bottom, or all over the wall ?
Additionally, what is the thickness of the damp wall and does it extend upwards through another floor above ?
The best course of action will be to deal with the source of the damp rather than just trying to cover it up, especially as persistent damp will eventually cause degradation of the structure which will be costly to put right.
A photo or two would be handy if you can manage it.
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Robert thank you so much for your reply to my query. The house was partly renovated when it was bought, it has no foundations or damp proof course. The ground floor outer walls are stone approx 500mm thick, on the inside the walls are made up of these 50 mm thick plaster blocks, I think carreaux de platre on the Placo website is what there known as in France and they appear to be working like sponges, ( the staining is 4 ft up the wall ) they are floor to ceiling and had been painted, not sure with what but it is flaking off. I’m not sure but I think the blocks must stand on a concrete floor which was then tiled, do not know if there was a membrane under the concrete. I think I’m digging myself into a hole again and realising there is no easy way out of this.
I’m just fed up looking at dirty flaking walls. Thank you.
Sounds like it’s rising damp. You could either take the wall down and rebuild to include a dpc, or try to inject a silicon based dpc but not sure how feasible it is in those plaster blocks.
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Now. I have never used it but I noticed a product by Silka ..who are a well known and respected manufacturer which is called a liquid damp proof membrane . Basically one drills a sequence of holes at low level and injects a watery substance which then penetrates by capillary action and sets and makes a waterproof membrane . Drilling into that plaster material is very easy ..and almost certainly the liquid would propagate in plaster .. filling up holes in the plaster is extremely simple with a tub of ready mixed renovation compound.. I would advise speaking with the “experts “ at LeRoy Merlin ….but at 120euro for the starter kit of solution seems worth a punt..I might suggest you read the reviews good and bad on Amazon Fr before being carried away ..
Doesn’t that just displace the rising damp elsewhere? Is sounds such an attractive (ie easy) solution but rumour has it that problem may return two fold several years layer.
Our maçon nearly had apoplexy when we mentioned. He views it as a total connerie.
(When he returns from holiday we are having remedial work to install a french drain and pozzolana gully along length of front wall which we hope will be a permanent fix).
If the internal floor is concrete then any damp underNeath has nowhere else to go but climb up the walls.
Riding damp doesn’t work that way ..the dampness keeps climbing upwards using osmosis until it hits an impermeable barrier . A damp proof course is just such a barrier ..
In some cases and if there was no Damp proof course , people could dig down a bite on the outside of the external wall and attach a damp proof plastic course to the exterior stone and replace and tamp the clay back up to the level it was at previously and then repeat with another section. ..Of course the individual bites would need to be sufficiently small that the walls don’t decide to shift
. But rising damp is not the only source of dampness in a house … Since these houses are rock and rubble and more rock sandwich external walls ,there is no barrier to rain penetration through the walls ..and failed rainwater pipes are a common source. The other is whether the house is occupied all year and kept warm ..otherwise condensation makes wet spots . In my case we would typically have the shutters closed for months in winter and no heating and no solar gain. .. That provides conditions for discolouration and even wall stains.
If it is carreaux de platre there really isn’t a simple solution. They work fine based on a dry surface - on your floor they will absorb and slowly crumble whilst staining brown through all but gloss paint (and that just traps the damp so they crumble faster).
Inserting a membrane or anything beneath is more work than replacing it usually - but otherwise it’s always going to absorb from an old stone floor.
Heat and ventilation can resolve things if it’s been unoccupied for a period
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Damp spreads horizontally as well as vertically, which is why so many early 20thC beautiful cement tiled floors are damp round the edges. And the variation in stone in old stone houses can make the injected dpc less than effective.
Mr @Squirrel13 …you are getting some very sound advice here from folk with ‘damp’ problems in the past. I sympathise with you.
May I ask how many square metres of wall you are having to suffer?. If quite small, I suspect the previous owner(s) did a cheap a simple trick here of trying to cover up a damp wall behind and also did not I produce a dpc almond the way.
If it’s a small area, I would be included to take the lightweight block wall down completely. You will them most likely see a rag tag wall behind with cement and whatever. This will need to cleaned out removing all the cement and then more typically redone with a sand chaux plaster. It will still be damp though if the outside wall is not treated in the same way and any roof, gutter, downpipe leaks are not fixed and if below ground, a ‘french drain’ not installed.
Easy peasy if you know what you are doing and have the time. All doable and just rip it out if annoying you!
Good luck as well!
Actually there is (well comparitively anyway), so don’t worry too much.
First things first. Can we confirm that what we are talking about is the interior face of an exterior stone wall ?
I have had the same problem in my own home and have fixed it in what is admittedly a somewhat unconventional way, but which was done 20 years ago and the wall is still dry.
First thing is to discover where this damp is coming from.
No doubt some decades ago the interior face of this exterior wall was just rough stone that was both damp and not very hygenic.
Someone decided to build a false wall in front of it, and they did it on the cheap. You describe the blocks as being white in colour, but if they were the water resistant variety they would be either blue or green to show that they are ‘hydrofugé’. These are of course more expensive, which is why someone took the cheap option and used the white, water absorbent, blocks.
You say that the wall seems to have been built on top of the edge of a ceramic tiled floor. As the ceramic glaze on such tiles is 100% waterproof to all intents and purposes, the problem you have is not ‘rising damp’ as such.
We need to go back to think about the properties of the original stone wall. The mortar it is held together with is probably a mixture of sand, clay, and cow manure, and as such is very vulnerable to degradation over the decades.
All sorts of insects will burrow into the wall to shield themselves from the winter cold, and this, plus the natural movement caused by hot versus cold, and damp versus dry, will cause the ‘mortar’ to slowly fall out of the wall.
So, the block wall will have originally been built with a gap between the back of it and the face of the original stone. In all probability that gap no longer exists at the bottom of the wall, and this is what is creating the ‘bridge’ through which the damp is penetrating through to the inner surface.
To verify this, knock a 4 inch hole in the wall about 6 inches up from the floor at a place where the damp is at its worst. Stick your hand through the hole and feel around for the ceramic tiles below. If there is no gap, or all you are coming up with is handfuls of wet sandy muck, then that is where the problem lies. It is this wet muck that is forming the bridge for the water to reach the inner surface.
Ideally one would remove this muck by knocking holes through the wall spaced at twice the distance from your elbow to your wrist. A mucky job that doesn’t do much for the condition of your fingernails. 
Don’t worry, there is a fix that avoids having to demolish the existing wall.
I just need confirmation that we are indeed talking about the inner face of an exterior wall.
Also don’t worry about the lack of foundations or damp proof course. My house is exactly the same and there is a solution which adequately compensates for such a situation.