Dry lining a damp wall - what does the team think

[Chataigner]

Advice please - the back wall of my kitchen (80cm thick rough stone wall with old lime mortar) tends to be damp, and being part below ground on the outside, is very cold and attracts condensation in summer. I'm planning to dry line it, but have some doubts about the type of insulation and the supports for the new surface. I have already injected a silicon product along the base of the wall to stop rising damp.

The normal support system used here is galvanised steel sections, with semi-rigid glass fibre or rock wool insulation, then plaster board over the top. I worry about the insulation absorbing miosture - would extruded polystyrene be better as it is inherently water proof ? Is there a better choice than plasterboard ? I'd like to hang kitchen cabinets on the wall, and something more solid such as OSB appeals - any comments ?

[mark270981]

you could do with lining the walls with something like this it maybe overkill but will be effective.

http://www.twistfix.co.uk/products/wate ... ducts.html

then if you used 50mm stud like this

http://www.insulationexpress.co.uk/C-St ... C-Stud.htm

or if you prefer 2 x 2 timber.

The stud will need to be strapped back to the walls in the middle to take the bounce out of it.


hope this helps

[tusses]

the part 'below ground' ? Is it in contact with the ground / subsoil ?
If so, it will all need to be damp proofed or tanked(from the outside) to stop rising damp.

I'd use timber for the studs (just cuz thats what I'm used too.) and have the studwork line up with where you want to hang your cabinets.

I'd use a damp proof membrane behind the insulation and a vapour barrier in front. I dont see a problem with plasterboard, once the damp is delt with.

Polystyrene, can be open , or closed cell - the closed one is warterproof.


I'm DIY, not trade for this stuff, so I may well be corrected

Rich

[mrgrimsdale]

Depends on a lot of very variable details.
Simplest is to live with it.
Repair old lime mortar with proper lime mortar (slaked lime not "hydrated")* and plaster with trad lime plaster with plenty of horse hair (or modern equivalent). This increases the insulation value and surface temperature by much more than you would expect.

Then paint with distemper or lime wash.

You then have a "breathing" wall and a bit of condensation or external damp ingress may not be noticeable.

Then keep well ventilated i.e. leave clear space in front of wall to allow air circulation and adjacent furniture on feet so that air goes underneath.

* The French are good at this and UK conservationists may buy french lime products in preference to UK equivalents.

[modernist]

I think I'd be looking to get air, rather than earth, against the outside as a starting point. Maybe a membrane then a drained pea gravel filled trench if it can't be dug clear.

Once the damp is dealt with, insulated plasterboard on battens or Galv with a moisture barrier on the inside and ventilation to the void from the outside.

I suppose it depends on how far you need to go and how "ethnic" you want to leave the inside appearance. In your climate you may be able to tolerate more damp than UK.

[telos]

the part 'below ground' ? Is it in contact with the ground / subsoil ?
If so, it will all need to be damp proofed or tanked(from the outside) to stop rising damp.
I'd use timber for the studs (just cuz thats what I'm used too.) and have the studwork line up with where you want to hang your cabinets.
I'd use a damp proof membrane behind the insulation and a vapour barrier in front. I dont see a problem with plasterboard, once the damp is delt with.
Polystyrene, can be open , or closed cell - the closed one is warterproof.

I'm DIY, not trade for this stuff, so I may well be corrected

Rich

You may well be corrected.
Don't do it like this, it will cause more problems!

Modernist's ideas sound about right.

Have a look at the first diagram, p2. on the Kingspan site download.

Never externally damp proof a solid (non-cavity) wall that has no damp proof course. The damp has to be allowed to escape from the wall so don't use cement based renders or pointing.

Leave a gap between the solid insulation and the stone (doesn't have to be ventilated as long as the wall can dry out from the outside).
Do not put a damp proof barrier behind the insulation, that must go directly behind the final plasterboard layer if you don't use a combined insulated plasterboard.
The damp proof strips behind and under the studs are really important to stop them rotting. (something to do with durability....? )

Yet more advice to chose from. Who's tonight's lucky winner going to be?

[woodsmith]

I live in a house that has similar walls, thick stone walls that have no damp proof course, and these walls have been lined with insulation backed plasterboard which has been dot and dabbed onto the wall. This is not a fantastic idea IMHO but was NHBC approved, although I think they are a shower. However they have been up for 13 years and where this was done properly we have had no problems at all.

I have redone one wall that they cocked up when they dabbed ordinary plasterboard to the wall and it showed up as damp spots where the dabs were. I ripped it all off and put a breathable membrane over the wall, screwed roofing lath horizontally (which I used to level up the wall as it was well out) then fixed treated 2x2 battens with kingspan in between. Finished it off with foil backed plasterboard. If the wall had been particularly damp I would have looked to add some ventilation between the wall and the insulation.

Hope that helps

[thatsnotafestool]

... I have already injected a silicon product along the base of the wall to stop rising damp.

...

Sorry to rain on your parade but I have yet to find a silicon or any product that is effective as a barrier in stone walls simply because there are so many many voids that you can pump gallons in and it just runs any and everywhere other than where you need it.

If you are going down the high tech route (although Jacob's approach has more merit IMO although tad difficult to nail cabinets up!) then a vapour barrier is essential.

Loads of excellent information here http://www.spab.org.uk/advice/technical-q-as/

[Chataigner]

Wow, such a wealth of feedback, thanks everyone.

I will be helping the aeration from the outside with a gravel filled drain along the below ground section of the wall, and because it is built up from the solid rock on which we live, there should be very little contact with the subsoil. As for the silicon compound, yes of course there are cavities that cant be filled, but then moisture does not wick across cavities either, i've found the stuff very effective, if not a 100% effective solution.

Jacob - i hear what you say, but the level of damp is quite severe as the wall is at the foot of a slope it tends to collect water at the base. I've tried the traditional approach for several years, and it's much better than it was, but I feel the need to go a step further, using waterproof materials that were not available to the guys who built this place in the 1600's.

Looks like damp proof membranes to isolate the wall from the insulation etc. followed by steel studding, semi-rigid insulation and then a vapour barrier and plaster board.

Thanks everyone - watch this space in 5 yrs time and I'll tell you how I got on !

[Chataigner]

PS. As for putting loads of horse hair into the plaster, my horses have been contributing to this approach for years, we have bags of the stuff in the barn collected every tile we groom them. Long fibre tail hair is best, but all of it works to some degree.

[modernist]

PS. As for putting loads of horse hair into the plaster, my horses have been contributing to this approach for years, we have bags of the stuff in the barn collected every tile we groom them. Long fibre tail hair is best, but all of it works to some degree.

In my last place which was 250 years old we were hacking off the said horsehair plaster in one place and my cat stuck her head in for a look. Came out covered int he biggest ticks I've ever seen.

I used an injected damp course, dry lined with 50mm PU backed plasterboard on big dabs and sealed the inner surface with a paint on waterproof membrane. I did not vent the void but there was a huge draught coming out of the electrical sockets. Purists would seal the patress boxes but it is not necessary and even the BCO's have eased off about interstitial condensation now as it usually doesn't happen. I used building paper under solid timber floors on battens. It seems you are more likely to suffer from condensation damp in a 70's council flat.

[mrgrimsdale]

......... Purists would seal the patress boxes but it is not necessary

OK if you don't mind draughts!
It doesn't take much draught to complete nullify the insulation values. I'm having all services surface mounted on our insulated studding so there won't be any holes at all. Also sealing all joints and edges with tape or mastic as necessary.
Chapel conversion nearby has high spec sockets all over the place. This winter they had to gaffer tape over as many as possible, to reduce the draughts. Last place I lived in had 6" insulation in the attic ceiling. Toasty warm on any still day. Any wind and the temp fell rapidly to approach outside air temp, due to inadequate sealing around the eaves. Had to stuff carpets and cushions around the perimeter.
I will also be ventilating behind the studding. I've hung polythene over the worst bit of the stonework behind the studs. Water drips off at the bottom and is taken up by the earth as there is an earth sub floor. Without this there could be a problem.
k value of stone is so high (granite 2.30) that you can just about ignore it for heat calc purposes. Phenolic foam k value is .02. This means 25mm of foam has the insulation value of 2,875mm of stone i.e. approx 1 inch to 9ft!!!
This also means that lightweight plaster (ancient or modern) applied direct to stone, has a surprisingly large effect on final U value, and hence surface temp and condensation.

[thatsnotafestool]

....
This also means that lightweight plaster (ancient or modern) applied direct to stone, has a surprisingly large effect on final U value, and hence surface temp and condensation.

Not sure what you mean. Can you explain a bit more?

[mrgrimsdale]

....
This also means that lightweight plaster (ancient or modern) applied direct to stone, has a surprisingly large effect on final U value, and hence surface temp and condensation.

Not sure what you mean. Can you explain a bit more?

Lightweight plaster has more insulation value than normal, due to addition of stuff like perlite granules. Trad lime plaster can have hair/straw added, plus being aerated by nature, so is more insulating than dense plaster (e.g. gypsum etc as used for finishing coats or mouldings).
More insulation means higher surface temperature which means less condensation, a.o.t.b.e.

[thatsnotafestool]

That was my understanding but as I read your OP it read as if there was more condensation after plastering..which I didn't understand.