More lime novices, insulating finish

[numberwang]

Hi, would like to ask advice on best approach on bedroom wall finish. Our house is a 1790 Farm cottage with one Victorian and one 1990’s extension, and is not listed.

One bedroom in the Victorian ‘wing’ has 3 solid walls that are external, to cut a long story short we are undoing the previous owners DIY to expose fireplace and found the original lime mortar shot (was being held on by layer of polystyrene backed plasterboard)!

So in terms of reinstatement (we are currently down to brick) and thinking of 15mm wood-wool board to insulate covered with hemp lime -all from TyMawr which is our nearest supplier. We want to blend it in to meet the original curve of ceiling so not planning to drywall it.

The exposed bricks are a little uneven, is it worth putting on a base coat of lime (sorry if not right terminology) to even things out before attaching the board?

Also is cork board be a better choice for insulation?

Thanks

 

[TheSpid]

Make sure you have absolutely no damp all before using hemp plaster - my brother used it [from Ty Mawr] on his chimney and it went mouldy. He was not impressed. Ty Mawr weren't interested at all.

If it were I, I wouldn't bother with insulating boards and would just lime plaster, but I believe Ty Mawr recommend cork board over wool board. They have a leaflet on their website about insulation.

 

[Crazycacti]

Similar situation to mine. Got a lot of external walls back to stone on the inside and looking at the different solutions at the moment.

Later in the year I'm going to have a look at the insulating plaster Eden Hot Lime do. Looks to be basically hemp lime with some perlite thrown in. Some good reviews on it and can go on in pretty thick coats.

The other potential solution I've seen is a hempcrete kind of idea where they stud the wall out a little and pack it in against the wall using a board on the studs and move it up each time so you get a good 40mm+ layer of hempcrete against the wall. I've got a lot of discoloured stones in my walls (high iron amount in some of them it seem) so this looks the option less likely to leach colour through but still in two minds about it.

I've also thought about the boards but not massively happy about putting so many fixings into the walls if honest plus the dubbing out behind would have to be pretty decent to ensure a perfect flat background for the boards to fix to with no tiny voids.

 

[paulc]

A work colleague used hemp plaster in her little cottage. From the short talks I've had with her, she is not impressed with the stuff.

As for the wood fibre boards, I'd go for the 25mm sheets on the grounds that more is better. You'd also get a flat surface to plaster over.

 

[a twig]

On the other side, I've used hemp with no issues at all, the extra cost of it is offset by the lower vat as it counts as insulation

I've only used with it NHL though. It is heavy going to get it on the walls but it was brilliant for any dubbing out work as well as the base coat.

 

[TheForge]

I’ve used putty based hemp plasters with no issue, but in persistent damp I can imagine it promoting mould and potentially rotting the hemp shiv if the plaster hadn’t been able to carbonate.

It’s very easy to apply and can potentially be put on thicker than ‘normal’ mortars.

Hemp plaster seems to be warmer to the touch but to actually effect the u-value of a wall it would need to be applied extremely thickly.

 

[numberwang]

Ah thanks for the heads up on the hemp, I’ll look at some other options. We’re trying to match up to a depth of about 2.5cm where the original plaster ceiling curves down to form the wall, so was thinking base coat, then wood wool board, then some sort of top coat would get us there. The ceiling is in pretty good condition bar a little cracking..

 

[Lime]

Successfully insulating a wall that was not designed to be insulated is not an easy task, impossible over the long term if the wall is damp.
Using material that will decompose or alter in damp conditions will make it all the more difficult.
Not only do you have to prevent water ingress through the wall bricks causing damp problems but also prevent any air or moisture from the room condensing on the sometimes colder interface between the insulation and the brick.
The insulation will prevent evaporation and the water content build up over time.

 

[numberwang]

Ok, not sure I follow the last post sorry. There are no signs of damp anywhere, it’s just we have 3 external walls exposed to cold rather than adjoining other rooms. The outside is rendered.

We were assuming the previous owners lined the walls with polystyrene to make warmer for that reason, I want to replace with something breathable. The wall is a brick and a half deep (40cm?) we might insulate the outside at some point when we’ve done more of the essentials!

Thanks

 

[Lithgae]

You may wish to look at diathonite evolution. I came across this product when I was looking for breathable, insulated render, and considered alongside bauwer light, other renders and wood fibre boards etc. I did a lot of research and it seemed to have the best insulation values of all the insulated renders and plasters I looked at, but I wasn't convinced that it would have been durable enough for an external render in the climate where I am in Scotland, seemed better suited as an internal plaster.

If I was gutting an internal room back to brick/stone though I would consider giving it a go. Hardest thing I found was actually finding a plasterer that was interested in working with it, or for that matter anything that wasn't gypsum or cement!

 

[numberwang]

Thanks for the reply, we ended going for a hybrid solution after getting some advice... one wall and alcove has an incredibly hard base coat we can’t identify so we’re going to Celenit board that then lime hemp & top coat, the other side we will use consolidation layer, EcoCork and topcoat.

We hopefully start boarding out at the weekend so will report out how it goes. I worked with clay in a previous life and have rendered before so attempting DIY job with the lime! I’ll start where the wardrobe goes to hopefully get the hang of it

 

[numberwang]

You may wish to look at diathonite evolution. I came across this product when I was looking for breathable, insulated render, and considered alongside bauwer light, other renders and wood fibre boards etc. I did a lot of research and it seemed to have the best insulation values of all the insulated renders and plasters I looked at, but I wasn't convinced that it would have been durable enough for an external render in the climate where I am in Scotland, seemed better suited as an internal plaster.

If I was gutting an internal room back to brick/stone though I would consider giving it a go. Hardest thing I found was actually finding a plasterer that was interested in working with it, or for that matter anything that wasn't gypsum or cement!

I’m curious about your outside insulating render, what did you use in the end?

 

[Lithgae]

I’m curious about your outside insulating render, what did you use in the end?

I didn't in the end. I was getting cement render removed, and I figured that it would make sense to re-render with an insulated render, and Bauwer and Diathonite both looked like good options. I spoke to the Scottish lime centre trust and Historic Scotland, and both were interested but cautious, and the reason the gave was climate. We are quite exposed. However, the main reason was that the front of the house is Ashlar Sandstone, and even if we were allowed (conservation area), I wouldn't want to cover it over. This would have meant a very visible edge where the render stopped, because it would need to be thick to be effective. It would also have meant leadwork flashing to cover at the top, and it was just starting to get too expensive. I think I would be keen to try the Diathonite internally, it looks good, but it is expensive. It would certainly be cheaper to use say wood fibre and plaster I think.

In the end I just left the stonework exposed and repointed. Will try and post a pic later.

 

[numberwang]

Sounds complicated Lithgae.

Progress very slow here, bricks look normal but insanely hard and had to upgrade drill! Hopefully wood-wool boarding out will speed up over weekend.