Doing some renovations at STM towers which involved chiselling off the plaster from 2 walls covered in old, cracked blown horse hair render. This was laid really thick , up to 60mm in places where successive plaster coats have been added to cover up cracks . The walls , both face externally N /NE facing are now back to brick with a course of ash block at head height for some random reason, then brick again , then wood wall plate.Â
This has made the room colder , mostly down the gap above a window that has spaced timber above it so is open to the cavity. Due to the structual movement of the house ( near road , with drains the busses enjoy driving into causing the house to shake as its built on cathedral footings on gravel ) most modern plastering tends to crack over time.
SO , im thinking of getting some expensive Lime based insualting plaster which appears to contain either cork or glass fibre beads . These lighten the weight of the mix and add a good level of insulation for the thickness. Its not cheap at 5 x the price of the usual pre coat and finish plaster, but apparently adds significant levels of insulation.Â
As its got Lime in it apparentlly its better suited to older properties with some movement and has a degree of flex.
Has anyone actually had any experience of insulated Lime plaster, either applying it or getting it professionally plastered before I spend load of cash , or any ideas for a thin , effective insulating finish ( not cellotex 100mm as the room is small enough as it is..)
You could consider Stieco wood fibre insulation with lime render over the top.Â
I would suggest speaking to a surveyor who has experience in that area though so they can model potential make up and check that you aren’t creating another problem.Â
if you are south east I know someone who would be able to advise
I know my dad had issues with it, mainly getting it on to the required spec. The most thermally efficient its spray applied as it creates the least dense layer, and the really big numbers come from quite a thick layer.
He struggled to any contractor and the one who did, travelled up from England somewhere, did a shot job and left under a mutual agreement. It was finished with trowels at an increase eof density and acceptance performance would suffer. The finish os less hard than traditional plaster (lime or gypsum)
In other areas of their conversion wood fibre panels and cork block tile things were used.Â
I am in the process of insulating my stone property using various natural materials, it has been an interesting exercise.
I also work solely with lime mortars/clay and similar natural building materials as my day job, so it's all straightforward for me but it isnt rocket science either, it's typically labour intensive though!
On one of my gables I have used hemp plaster which is about 30mm thick as a straightening coat. It is a good insulator and noticeably warmer - hemp shiv is a hollow fibrous material that is naturally insulating. In time I will be adding sisal wool between stud and then woodfibre carrier board/lime plaster and then limewash finish. You could go much thicker on the hemp plaster (it's possible to build solely from hempcrete) although drying times become an issue. Hemp plaster is easy to use and mix, and you can buy the hemp from farm supplies as horse bedding and mix with quicklime in a belle mixer. If you wanted a thicker build up then you would put in stud and then shutter it and fill with lime in courses.
If you went for hemp lime, you could either use a fine hemp finishing coat or go for a lime/sand type finish, depending on your personal preference
Other walls I have used cork boards against the stone - typically 40mm - and then a build up of sisal wool between stud, carrier board and lime plaster again. Cork board is super easy to apply - cut to fit, and then 'glue' to the wall with lime mortar. It is very insulating and is damp resistant/breathable. Downside is cost but it is quick and relatively easy to use. Comes in a variety of thicknesses. Personally I think cork board is one of the easiest systems with excellent insulation and I would be seriously thinking about it if I had limited space to work with. I am pretty sure you can plaster direct to the cork, but i'd need to check to be sure
Other walls I have used sisal wool against the stone straight between studwork, then carrier and lime plaster
All these materials are good insulators, but of course if you are only using 10Â or20mm then the actual insulation isnt going to be great. I would be aiming for a minimum of 40mm, that said anything is better than nothing.
Check out Ty Mawr and Mike Wye- both have heaps of info on natural insulation systems with diagrams of their recommended build ups. They will sell you everything you need, though of course if you are confident it is possible to make the materials from the constituent ingredients which you can source locally
Totally happy to answer and questions
You could consider Stieco wood fibre insulation with lime render over the top.Â
I would suggest speaking to a surveyor who has experience in that area though so they can model potential make up and check that you aren’t creating another problem.Â
if you are south east I know someone who would be able to advise
This.Â
I used to sell Pavatex insulation and Baumit renders/plaster.
You could pop a thin 25/30mm board on then render. I guarantee it would improve warmth over a thick insulating plaster.Â
The modern lime renders are very good.
I've done the outside of our solid walled stone + red brick (from extensive repairs in the 50's) cottage with a perlite mix. 1 nhl 3.5, 1 lime putty to 5 perlite P321. It's much cheaper than premixed stuff. I don't have any u-values for it, but I belive It's not too far away from the pre-mixed stuff.Â
