Renovating plaster vs Thermal boards

Hiya,

Firstly, don't worry, I'm not going to ask about rising damp. What I do have is a condensation/ lower wall crumbling plaster problem. The trouble is on limited sections of 2 cold exterior walls (exterior areas in permanent shadow), solid brick 1910s mid-terrace. The problem was exacerbated by a mix of poor central heating (fixed now) and badly placed heavy furniture...

In one area plaster has 'blistered' away from the base layer of rendering (sand and cement, I believe). Another problem is on a closed-off chimney breast on the shared wall. There's crumbling plaster where the chimney meets the wall - it looks to be gypsum, so is basically just flaking away with the slightest moisture. The previous owner had DPC injection over a decade ago and god knows what mix of plaster and rendering.

To cut to the chase, I've had an independent surveyor advise that the exterior walls need to be hacked back to brick in the affected areas only plus another 300mm above and replaced with limelite renovation plaster or similar and the areas kept free of heavy furniture.

A surveyor from a preservation/ damp-proofing company went one further and advised hacking back to brick the whole of both exterior walls and fixing thermal boards with an integral vapour barrier directly to the brickwork using brick plugs.

Both surveyors agreed that the closed off chimney needs cowling, then reopening and cleared out. The independent then advised just tanking and replastering, the other suggested 'cementitious slurry' (???) and more thermal boards on the chimney breast.
They also both suggested extractor fans.

Question - what would be best choice overall? I've no experience with thermal board but I've reservations with a number of things:

1. I've got to mount a radiator back onto the wall being boarded, plus there are cables and sockets - wouldn't these just breach any vapour barrier?
2. If the cold exterior wall is still cold and damp, would this risk damaging the board?
3. What about if in future I wanted to mount things on the walls?
4. I understand boards on the exterior walls, but is there really any point in thermo boarding a chimney breast on a shared wall?

Ideally I'd want to keep all walls as breathable as possible so moisture isn't trapped - I've already had problems from previous owners and next door tanking both sides of a shared extension wall. The brickwork was still damp and it rusted away a power socket housing and blew a fuse (but that's another story).

Thanks

Hi mate I would sort the chimney out so it can air properly.. the walls I would suggest a k11 slurry which will prevent any moisture penetrating back through then apply a renovating plaster and reskim..

Thermal boards may work for some time but if not done correctly the moisture will find somewhere to get through.

K11 ( from sovereign ) applied with total coverage on surface will protect the new plaster

There is another more expensive product called natcem which has same effect.. not a slurry but a heavy mortar.. used for taking systems etc

Hope this helps

Couple of options with damproofing..

1 hack off 1.2n from ground level. inject DPC cream, S&C with waterproofer then skim

2 which I prefer tbh especially with solid 9" walls, hack off 1.2m from ground level, salt inhibitor, use a taking slurry many brands on the market Soverign and kingfisher some of the best, S&C with waterproofer and skim..

The insolation boards you mentioned have a vapor barrier but personally I prefer to stud the wall out rather than dabbing them, this will also solve the issue but you will lose some m2

Be aware of thermal mass implications caused by use of thermal boards, ask some of these experts about it ,if they don't know,don't ask any more,
ps would a breathable plaster not be sufficient ie lime

Right. I approached mr thermal boards who told me that I shouldn't have anything to do with renovating plaster. Limelite or otherwise. I smell salesman.

Told me it's too light and lets salts through...

You can use a damp proof membrane fixed to the brick work with plastic plugs then coat with sc should stop any thing comming through

time123 said:

Right. I approached mr thermal boards who told me that I shouldn't have anything to do with renovating plaster. Limelite or otherwise. I smell salesman.

Told me it's too light and lets salts through...

Click to expand...

Lol. It's got salt inhibitors in it

Exactly Arti. I'm not opposed to insulation boarding, but I am opposed to people who are on commission and wont enter into an open conversation.

In reply to some of the other posters, I don't have a problem with damp or water ingress from the walls. Basically I've got 2 areas plaster damage caused by prolonged contact with condensation and I just want an idea of the best plaster to replace the damaged rendering with. Then there's the chimney breast with the flaking gypsum that's taking the wallpaper with it - possibly due to salts from the flue.

I've had readings taken from one cold wall. One side of the bay window registered at about 11 or 12 degrees (it's in permanent shadow). The other side of the bay (that gets sun) was about 4 degrees warmer. Would thermal board really help equalise this anyway?

Read through god only knows how many posts. Many thanks to everyone who seem to have solved these problems many times over (after a wee bit of disagreement here and there).

Will break into the chimney and clear it out and cowl it properly. Ensure that the plaster isn't going down to the floor behind the skirting on it, and on the walls go for a more breathable plaster. I found some evidence this morning that the plastering after the original DPC injection was largely a DIY job, which probably explains the hodge podge of different plasters in various states of decay I'm finding on every wall.