Lime Plaster

[JessUK98]

I've always had a problem with "damp" and mould in nearly all rooms with external walls (the front of the house basically). This is probably down to my not being very good with opening windows and drying clothes in front of the fire etc (now that I'm older and wiser I've seen the error of my ways) and the previous owners skimming using pink gypsum (solid stone house). The plaster feels blown in many places. In one of the rooms I've basically hacked all the pink gypsum off underneath the window (it literally fell of with hardly any effort whatsoever) and there was black mould behind the plaster in some places.
Now, I'm not sure what is underneath the skim plaster though. It's kind of grey and grainy for want of a better word, so I'm not sure is that is the base coat or not and what they have used for this layer (I'm hoping that it isn't asbestos now....). Would this also need to be hacked off, or is it likely to be breathable?

Could I just put lining paper over this layer of plaster - I've seen Erfurt wallrock fibreliner which allows the walls to breath. Then I was thinking of something like an earthbborn interior claypaint to paint the lining paper with. Or would it be better to skim the wall again with a lime finishing render e.g; http://www.limestuff.co.uk/external-and ... cabamento/
I've never plastered a wall before though (and I believe lime plaster is harder to work with), and trying to find a plasterer that has used lime plaster or will get back to me is like trying to get blood out of a stone (which I'm surprised about given there must be loads of stone houses around here).

The section of wall I've removed the pink gypsum from is markedly improved, and I've since invested in a second dehumidifier (I leave one in the kitchen all the time) and this has really helped.

[redsturgeon]

These people are near me and might be worth a call.

http://www.thelimecentre.co.uk/advice.htm

John

[bungeejumper]

"Grey and grainy" sounds like the bonding coat ("scratch coat") plaster that was used on our 19th century stone-built house. It was halfway between plaster and cement mortar, TBH, and it had been applied coarsely and in considerable thicknesses where necessary. One of its best attributes is that it sticks like anything, and it sets quite hard. The plaster, whether gypsum or lime, would then take a successful 'key' to it and you'd get your smooth, stable finish.

Our builders had to hack off an entire wall of this stuff (because a leaking gutter had destroyed all the plaster over a 30-year period before we bought the house), and they replaced it with a modern equivalent, http://www.wickes.co.uk/British-Gypsum- ... g/p/220055 . It worked fine, and in fact they skimmed it over with modern pink gypsum and there have been no probs in the intervening 23 years.

I think you're right to suppose that damp in the rooms has been the cause of the mould, but I'd be a bit surprised if it's all happened during your ownership - that sort of thing usually takes much longer to get that bad. Maybe your predecessors under-heated the rooms, or maybe they used damp sources such as propane heaters?

Either way, you need to think at least a little bit about using lime plaster for 'edge' and minor-damage repairs, because it's a bit of a beast to handle and it can take forever to dry before you can paint it. If you feel confident, however, then good for you! The following link will probably help: http://www.buildingconservation.com/art ... eplast.htm

Good luck!

BJ

[JessUK98]

I think you're right to suppose that damp in the rooms has been the cause of the mould, but I'd be a bit surprised if it's all happened during your ownership - that sort of thing usually takes much longer to get that bad. Maybe your predecessors under-heated the rooms, or maybe they used damp sources such as propane heaters?

Quite possibly. Before I bought it, it used to be a holiday home for many years. They had also blocked one fireplace in the living room (and must have removed a back boiler as when we were opening it back up to add a multi fuel stove we found a lot of left over copper pipework (and an absolutely gorgeous slate lintel)). They had completely removed another fireplace (which would have been the one in the kitchen - they've knocked through the lounge/dining room and kitchen to make one room, and added an extension on the back for the kitchen).
Dread to think what other horrors await me as I start to update other parts of the house.

[bungeejumper]

Quite possibly. Before I bought it, it used to be a holiday home for many years. They had also blocked one fireplace in the living room (and must have removed a back boiler as when we were opening it back up to add a multi fuel stove we found a lot of left over copper pipework (and an absolutely gorgeous slate lintel)). They had completely removed another fireplace (which would have been the one in the kitchen - they've knocked through the lounge/dining room and kitchen to make one room, and added an extension on the back for the kitchen).
Dread to think what other horrors await me as I start to update other parts of the house.

Sounds like my kinda renovation. We had roof, walls, windows, four collapsing ceilings and three collapsing floors to sort out before we could start in on replacing the plumbing and the wiring. (The doors were all right, though. ) Have fun!

Sealed off fireplaces should have at least one air vent in them, so as to keep a modest drying airflow moving up through the flue and the stack. They don't need to be big, and there are some nice designs available. Enjoy your project!

BJ

[Mercenary]

Hi

My first post, hopefully not too late!

Problem is a solid wall needs to breath which means lime mortar and plaster and no cement (mortar, render, etc) or gypsum based plaster (like you seem to have). Also lime will not readily adhere to a gypsum plaster or even sand and cement render (assuming that's your backing coat). Lime plastering is more involved and takes longer, including repeat visits, so is not liked by most plasterers. Yes, they are very hard to track down, turn up, and get a quote from. I went to Ty Mawr for a course in the end!

Maybe your grainy backing coat is lime in which case you could possibly get a lime finish coat applied. Probably not. In which case, hack everything off and lime plaster, reapply a gypsum finish coat and pray, or try your wallpaper stuff. An alternative is to have it dry lined (and insulated) as is, ensuring this is done correctly (vented to outside or sealed very well) to prevent interstitial condensation and mould. Space permitting, you could possibly use insulated plasterboard (won't breathe) or frame the wall and add insulation (breathable or not) and finish with plasterboard (non-breathable) or wood fibre board skimmed with lime plaster (breathable). The Ty Mawr web site has specifications for the breathable walls. Breathable paints will be required for breathable walls.

I have been pragmatic myself and just re-skimmed over parts of rendered walls because of the work involved in removing the render (and no signs of damp) but will be boarding out the walls I can because I need the insulation. Due to some guy previously using a cement mortar on the stone walls, I will probably use non-breathable dry-lining with an insulated air gap for dry walls. At least do a test piece to see. Maybe Limelite (see below) for damper walls (once I have cured the cause of any damp where possible).

Just to add another twist, there is a product called Limelite Renovating Plaster which has some cement but a high lime (breathable) content and does not need the work of a lime plaster. It's more like a normal gypsum plaster to apply (in both method and the suitable backgrounds), although some plasterers say it's harder to apply. Definitely worth a look.

Hope this helps.

[bungeejumper]

Problem is a solid wall needs to breath which means lime mortar and plaster and no cement (mortar, render, etc) or gypsum based plaster (like you seem to have). Also lime will not readily adhere to a gypsum plaster or even sand and cement render (assuming that's your backing coat). Lime plastering is more involved and takes longer, including repeat visits, so is not liked by most plasterers. Yes, they are very hard to track down, turn up, and get a quote from. I went to Ty Mawr for a course in the end!

....I have been pragmatic myself and just re-skimmed over parts of rendered walls because of the work involved in removing the render (and no signs of damp) but will be boarding out the walls I can because I need the insulation. Due to some guy previously using a cement mortar on the stone walls, I will probably use non-breathable dry-lining with an insulated air gap for dry walls. At least do a test piece to see. Maybe Limelite (see below) for damper walls (once I have cured the cause of any damp where possible).

Aha, another lime plaster nut! Great contribution, and welcome. Yes, my wife has got her "lime certificate" - she's done the whole thing, slaking her own lime mortar and all that. And like you, she rails at the sight of other people using cement mortar on external stone walls. "They'll regret that. Just wait till the frost gets under it and the wall won't dry out." (Etcetera.)

You're also right, though, that you have to be a bit pragmatic about when and where you use lime plaster inside a house. The chances are that some builder somewhere will have updated walls and ceilings with gypsum, and eight times out of ten it won't have cause any conflicts or problems. (It's the other two that you have to be aware of.)

Then again, lime plaster doesn't suit modern life very well. It can take 3/6 months to dry out properly, and then when you've finally painted it with limewash it might still get damp in winter. We have a rental property which happens to be listed, and it isn't easy to persuade tenants that a few damp shadowy patches on the walls during periods of cold wet weather are considered "normal", and that they don't denote that the property is substandard - rather, it's exactly the traditional way that the listed buildings people want it to be.

Compromises, compromises. Thanks again.

BJ

[Mercenary]

Hi bungeejumper

"Yes, my wife has got her "lime certificate" - she's done the whole thing, slaking her own lime mortar and all that". Crikey, not sure I'm that much of a nut! She sounds great though. Would be a real asset here.

I have the typical older stone building which has been updated in the 1950's and then 1970's. What I learnt (to my cost to put right) is that, in general, is to match technique to the property age - e.g. lime in the stone bit but not in the 1970's bit and vice versa. I originally had tanking material put over the stone walls which you could then gypsum plaster over. It did not seem right so I left it "as is" and when I did take it off some three months later, the damp smell, etc told me I had definitely dodged a bullet!

Tough one.

[bungeejumper]

I originally had tanking material put over the stone walls which you could then gypsum plaster over. It did not seem right so I left it "as is" and when I did take it off some three months later, the damp smell, etc told me I had definitely dodged a bullet!

I've never been very sure how I feel about tanking, because often people use it to cover up a pre-existing damp problem without dealing with the cause. And it might buy you 20 years of dryness, or maybe only one before you get the tell-tale seepage and then you open it up to reveal a sea of grey mould. (Been there, got the T shirt - and no, it wasn't me that had done the tanking.)

I once had a stone-built cottage where the ground floor had been tanked up to six feet with some corrugated stuff called Newtonite under the (gypsum) plaster. I was urgently warned not to pierce the tanking - which kind of kaiboshed the idea of rewiring the house, because how else was I going to install the power points? So I made a few exploratory holes and lo and behold, it was all sweet and dry under there. My neighbour, however, had got the furry grey mould under hers. You never can tell.

BJ

[JeremyWils]

I recommend doing a slight render to your outer wall

[Johnspenceuk]

Hi

My first post, hopefully not too late!

Problem is a solid wall needs to breath which means lime mortar and plaster and no cement (mortar, render, etc) or gypsum based plaster (like you seem to have). Also lime will not readily adhere to a gypsum plaster or even sand and cement render (assuming that's your backing coat). Lime plastering is more involved and takes longer, including repeat visits, so is not liked by most plasterers. Yes, they are very hard to track down, turn up, and get a quote from. I went to Ty Mawr for a course in the end!

Maybe your grainy backing coat is lime in which case you could possibly get a lime finish coat applied. Probably not. In which case, hack everything off and lime plaster, reapply a gypsum finish coat and pray, or try your wallpaper stuff. An alternative is to have it dry lined (and insulated) as is, ensuring this is done correctly (vented to outside or sealed very well) to prevent interstitial condensation and mould. Space permitting, you could possibly use insulated plasterboard (won't breathe) or frame the wall and add insulation (breathable or not) and finish with plasterboard (non-breathable) or wood fibre board skimmed with lime plaster (breathable). The Ty Mawr web site has specifications for the breathable walls. Breathable paints will be required for breathable walls.

I have been pragmatic myself and just re-skimmed over parts of rendered walls because of the work involved in removing the render (and no signs of damp) but will be boarding out the walls I can because I need the insulation. Due to some guy previously using a cement mortar on the stone walls, I will probably use non-breathable dry-lining with an insulated air gap for dry walls. At least do a test piece to see. Maybe Limelite (see below) for damper walls (once I have cured the cause of any damp where possible).

Just to add another twist, there is a product called Limelite Renovating Plaster which has some cement but a high lime (breathable) content and does not need the work of a lime plaster. It's more like a normal gypsum plaster to apply (in both method and the suitable backgrounds), although some plasterers say it's harder to apply. Definitely worth a look.

Hope this helps.

Hi enjoyed your post very informative

John

[JessUK98]

Gosh, this post is a blast from the past. I’m currently getting the exterior repointed. Quite a job finding somebody. Anyway the old fella was like “somebody has patched this in cement! That’s not going to be fun to remove”. But that’s the polite version.