Is it essential to remove standard plaster?

[Anys9]

Having sandblasted, lime mortared, and lime rendered the exposed gable-end of farmhouse, (expensive,) now faced with advice to remove standard plaster inside and replace with lime plaster. The wall (no DPC) is stone, rubble-filled, dates back to 17th century. It was full of trapped rainwater which is why the above's been done, to let wall 'breathe.' We're using dehumidifiers inside to help get water out of wall. Do we really have to remove the internal plaster next, which is a messy, dusty business and extremely disruptive? And what about putting an airbrick or two with pipes through this wall, would that help? Also will scraping emulsion paint off wall and replacing with clay paint help matters? Would appreciate your advice.

 

[Me!]

I can't comment if this applies everywhere, but in central France where they have a lot of old stone houses (and it does get very damp in winter), the current building practice with these old houses seems to be to keep the outside of the walls completely breathable with lime mortar and exposed stone. But on the inside they use waterproof coatings like cement render and fibreglass wallpaper to keep the inside dry. It does seem to work OK.

 

[skier-hughes]

I'm doing it to my house, and yes it is a very very messy and disruptive business.
My understanding is that the wall really needs to breathe both ways, so internal moisture can enter the brick and go out side if neccessary, or heavy moisture from the outside can make it's way through and disappear internally, surely a blocking of this movement leads to moisture retention in the wall which could cause other problems?

Graham

 

[Nemesis]

I believe in France much of the lime used is hydraulic. It's rather like using a cement mix.

Cement and glass fibre paper aren't something anyone with any sympathy for historic buildings would use.

 

[Anys9]

Thank you for your input, sadly we're planning to sell up as my husband is so disabled now, and our thinking is that anyone buying might want to do some building work (like putting lime plaster internally on the end wall) before they move in, so all the messy work could be carried out then. At present the Ebac dehumidifiers are making stains on the wall in question and we wonder if they're doing more harm than good. Certainly there's a lot of trapped rainwater still in that wall and it needs to dry out. The rainwater had even got into the electric socket boxes in the wall and these had to be resited on the wall surface. :roll:

 

[Welsh Builder]

The wall will dry out far quicker if the interior is lime too. The positive air pressure within the house will push the moisture towards the exterior provided the wall is breathable throughout. In many areas the tradition was to have roughcast render on the exterior with smooth lime plaster on the inside. The larger surface area on the outside helped create the pressure diferrential and alllow the wind and sun maximum opportunity to dry the exterior of the wall (thus pulling the moisture out). You need the combined push and pull.

As mentioned above, hydraulic lime is basically cement and does not breathe like real lime render made with putty.

 

[skier-hughes]

As mentioned above, hydraulic lime is basically cement and does not breathe like real lime render made with putty.

I'd disagree with this statement, from what I've been told by Lime green products, South Yorkshire Energy Centre, Limecraft, hydraulic lime is breathable. Tests carried out on my lime mortar, so that we could copy it show that it was built with an hydraulic lime several hundred years ago.

 

[Nemesis]

The level of that depends on the hydraulic lime.

http://www.buildingconservation.com/articles/lime/hylime.html

 

[Anys9]

Welsh builder wrote '...allow the wind and sun maximum opportunity to dry the exterior of the wall ...' What sun? We've had practically nothing but wind and driving rain here for months, the worst summer on record for many years, and that gable end wall is southwest facing too. Nearly forgotten what the sun looks like.