Green stuff under wallpaper - what is it?

TheJackah

We are pulling wallpaper off of a recent house purchase. It’s built in 1900. But underneath the wallpaper, there’s green stuff across the walls underneath it. 

Picture:

Does anyone know what this is?

Rummer65

I could be wrong but looks like distemper paint

Doozergirl

Paint?   It's not unusual to see colour on the walls.  

I'm not sure why it matters, the plaster is well and truly blown there, it should be coming off. 

TheJackah

Doozergirl said:

Paint?   It's not unusual to see colour on the walls.  

I'm not sure why it matters, the plaster is well and truly blown there, it should be coming off. 

Good spot, was too focused on the green stuff to even notice the issues with the plaster itself!

We were just worried the green stuff could be mould. 

TELLIT01

It's not mould but that plaster has completely gone!

[Deleted User]

...which means that wall's going to have to be hacked back to brick and replastered @TheJackah
That's making the big assumption that the whole wall's like it, not so if just that small area, sorry to be alarmist there.

FreeBear

Catsacor said: ...which means that wall's going to have to be hacked back to brick and replastered

Could be distemper, but that is more likely to have been used on ceilings rather than the walls. More likely a lime wash or casein paint.

If you are going to strip back to brick and replaster, please, consider using traditional materials such as lime plaster rather than modern gypsum. Whilst lime plaster is a bit more expensive, it is much more appropriate for a 1900s property with solid brick/stone walls.

Bendy_House

Has anyone had any experience of insulating plaster - containing additives such as cork to add thermal properties whilst still being able to breathe as a 1900s house ought to?

Eg: https://www.ecologicalbuildingsystems.com/products/insulation-and-materials/plaster-and-screed/insulating-plaster-and-screed

FreeBear

Bendy_House said: Has anyone had any experience of insulating plaster - containing additives such as cork to add thermal properties whilst still being able to breathe as a 1900s house ought to?

Secondhand experience - A work colleague used hemp plaster in her little cottage. She wasn't impressed.

Looking at some of those Diasen products, they are expensive (SecilTek ecoCork is only £10.40 per bag). The thermal performance is also comparatively low, so you need a pretty thick layer to be effective (maybe as much as 250mm). There is a limit to how thick you can apply the stuff (usually 20-25mm at a time). Gets very expensive very quickly.

If you want eco-friendly insulation at a price that isn't going to break the bank and is breathable, wood fibre or cork boards topped off with a lime render/plaster would be the answer.

Bendy_House

Thanks FB.

I personally know nothing about them, but was researching such products a good while back when a relative was looking at a cob-built house that needed work. I found insulated plaster which could be used externally, and other stuff for internal.

It was just a case of, if you must re-plaster the interior/exterior in any case, then might as well use this stuff - it'll give better insulation properties compared to 'normal' skim.

It would be fun to get it up to 250mm

The other stuff I found was as you said - a fibreboard that would be attached to the inside using 'pins', and would then be skimmed over.

FreeBear

Bendy_House said: I personally know nothing about them, but was researching such products a good while back when a relative was looking at a cob-built house that needed work. I found insulated plaster which could be used externally, and other stuff for internal.

Cob will generally be pretty thick walls to start with. Don't know what the u-value would be off the top of my head... I doubt that an insulating plaster would make much difference. But one thing is for sure, standard external/internal insulation materials such as polystyrene & PIR/PUR with a K-Rend type finish would be totally inappropriate and cause significant damage in the long term.

Edit - Interest piqued over cob wall construction. Can't find any definitive data aside from a couple of reports from the likes of SPAB. One report from the Devon Earth Building Association has a little quote from English Heritage - 

Currently [2008], English Heritage views the technical risks as unacceptable and does not recommend insulating earth walled houses either internally or externally.

Other reports suggest that because of the thermal mass of a cob wall coupled with its inherent air tightness, calculated u-values do not give a true indication of how a cob house functions thermally over the course of a year. To an extent, a view I could agree on.