Insulated render - anyone used this?

[Kaymo]

As you say you have made a cost/benefit comparison, would you mind sharing it?

I don't see why you think that cork based renders wouldn't be breathable at >50mm, stone walls at 600mm thick are still breathable, how breathable they would be will be a function of their vapour permeability and thickness. While I agree that EPS is breathable to an extent, these renders, and wood fibre, are significantly more breathable, 5-10 times more vapour permeable, so could go on 5-10 times as thick for the same vapour permeability.

There a few potential advantage of insulated renders that I can think of, compared to say wood fibre:
1. No thermal bridges.
2. One trade on site.
3. Can go straight on to uneven walls without levelling.

 

[gomez500]

Hi. Just found this thread. Has anyone got any experience of using a breathable render (such as Bauwer) on an internal stone wall that is cement rendered on the outside? I know ideally you want the wall breathable on both sides but I have a large stone house that is nicely rendered on the outside and I want to leave this alone. Render is painted and in very good condition with no cracks and I'm assuming is pretty watertight. I am hoping that if I use breathable on the inside, I am at least providing some breatheability and allowing any trapped moisture to escape.

 

[Kaymo]

I wouldn't see a problem with this. If humidity is controlled inside the house, and the cement render doesn't appear to have caused any problems to date then I wouldn't be too concerned. I think that common sense would say that the render on the outside of the house only needs to be breathable if wall is taking in water. For that reason, houses that don't have a dpc need to have to be free of render at the base level so any rising damp can breathe to the outside. The only other way for water to enter the walls is from the inside, and if the humidity inside is kept under control there shouldn't be an issue.

However, you might find that there are cheaper options for the inside, wood fibre and plaster?. I think the main component in terms of breathability on the inside is usually the final layer, the paint. Even EPS insulation, with plasterboard and a breathable paint would probably allow sufficient vapour transmission. I used EPS on an inside wall in my 200 year old house, but then this was in a bathroom and I also deliberately used impermeable paint to stop moisture entering the walls - but then my outside wall is not rendered so should breathe on the outside.

 

[gomez500]

I wouldn't see a problem with this. If humidity is controlled inside the house, and the cement render doesn't appear to have caused any problems to date then I wouldn't be too concerned. I think that common sense would say that the render on the outside of the house only needs to be breathable if wall is taking in water. For that reason, houses that don't have a dpc need to have to be free of render at the base level so any rising damp can breathe to the outside. The only other way for water to enter the walls is from the inside, and if the humidity inside is kept under control there shouldn't be an issue.

However, you might find that there are cheaper options for the inside, wood fibre and plaster?. I think the main component in terms of breathability on the inside is usually the final layer, the paint. Even EPS insulation, with plasterboard and a breathable paint would probably allow sufficient vapour transmission. I used EPS on an inside wall in my 200 year old house, but then this was in a bathroom and I also deliberately used impermeable paint to stop moisture entering the walls - but then my outside wall is not rendered so should breathe on the outside.

Thanks very much for your useful reply. You have highlighted another issue that should be addressed. The stone walls were constructed well before any sort of DPC existed. The walls are rendered right to the base so I may well now take some of that render off although there aren't really any noticeable problems inside. Base of ground floor walls are cold however and we do get condensation problems.

Back to the original query - I have considered other solutions like plasterboard and EPS and wood fibre but want to try and achieve 3 things, 1 - minimise the loss of space (even though room is pretty big), 2 - maintain breathability and 3 - increase insulation. My current plan is to get rid of the rather uneven original lime plaster from the wall completely (it was wall papered to hide the imperfections) and then re-do with bauwer. By doing this it should meet all 3 requirements but perhaps not the cheapest solution. I guess a lot of people might say that you want to try and preserve any lime plaster but I dont think you can add bauwer insulation over the top of the lime plaster? There are also parts of the wall in the window reveal that have been replastered with gypsum and I really want those bits to go. If I sacrificed the insulation requirement, could I reskim the wall as it is with a lime based finish or even Bauwer finish? Meets 2 of the 3 requirements and keeps the cost down.

 

[Kaymo]

The walls are rendered right to the base so I may well now take some of that render off although there aren't really any noticeable problems inside.

If you have suspended floors with ventilation, then it might be that any damp rising from the ground is able to escape on the inside, under the floor. If there are no problems then I probably wouldn't do anything, but I would be surprised if cement all the way to the ground and no dpc, didn't result in a wet wall at the base.

Base of ground floor walls are cold however and we do get condensation problems.

Are you sure that this is not rising damp? If the walls are particularly cold at the base that could be a sign of wet walls and that might be cured by taking some of the render off at the bottom. I heard a good test for condensation on another forum. The guy uses a ring of silicone to stick a small piece of glass to the wall in the area where the issue is, if condensation appears on the room side of the glass its condensation, if it appears on the wall side then it is a wet wall.

I would look at Diathonite Evolution as well as Bauwer. When I looked at it I thought Diathonite was marginally the better option, better u-value for same thickness. My problem was that I am no good at plastering large areas, and I couldn't get a plasterer locally that wanted to use it. You would definitely need to remove the lime plaster if you wanted to put on an insulated render/plaster. Its a very very messy job. I did it on one wall in the bathroom because that lath and plaster wall was falling apart due to the plasterboard that had been screwed on to it before we got here. After getting the lath and plaster off, I found an even older plaster direct to the stone, and once I got that off I had a lot of bags to take to the dump. The upside is that those old plaster layers are usually quite quick and so when you come back out to the same thickness its quite a bit of insulation.

You could of course re-skim over what is there, or overboard with plasterboard even, but that might bring the wall out too much if you have cornice/skirting etc to consider.

 

[gomez500]

If you have suspended floors with ventilation, then it might be that any damp rising from the ground is able to escape on the inside, under the floor. If there are no problems then I probably wouldn't do anything, but I would be surprised if cement all the way to the ground and no dpc, didn't result in a wet wall at the base.

Are you sure that this is not rising damp? If the walls are particularly cold at the base that could be a sign of wet walls and that might be cured by taking some of the render off at the bottom. I heard a good test for condensation on another forum. The guy uses a ring of silicone to stick a small piece of glass to the wall in the area where the issue is, if condensation appears on the room side of the glass its condensation, if it appears on the wall side then it is a wet wall.

I would look at Diathonite Evolution as well as Bauwer. When I looked at it I thought Diathonite was marginally the better option, better u-value for same thickness. My problem was that I am no good at plastering large areas, and I couldn't get a plasterer locally that wanted to use it. You would definitely need to remove the lime plaster if you wanted to put on an insulated render/plaster. Its a very very messy job. I did it on one wall in the bathroom because that lath and plaster wall was falling apart due to the plasterboard that had been screwed on to it before we got here. After getting the lath and plaster off, I found an even older plaster direct to the stone, and once I got that off I had a lot of bags to take to the dump. The upside is that those old plaster layers are usually quite quick and so when you come back out to the same thickness its quite a bit of insulation.

You could of course re-skim over what is there, or overboard with plasterboard even, but that might bring the wall out too much if you have cornice/skirting etc to consider.

Only one suspended floor and this has cellar underneath. I guess rising damp is unusual or even impossible when the walls continue down well below ground level. Certainly no evidence of rising damp.

I'll take a look at Diathinite - thanks although I'm sure I'm going to fall into same position as you with no local plasterers having experience with this sort of thing. I'm going to hack a bit of the lime plaster off to see how thick it is. There's no lath beneath as far as I am aware but is it still a messy job? I do have cornicing and skirting that would be a bit of a faff to redo but there is also a window seat with decorative panels beneath that would have to be moved outwards if the new job did not line up with the old. What I think I might do first is hack a bit of the lime plaster off to see what depth its on at. Can then decide on how effective any Bauwer etc may be. If not looking thick enough, I may well just reskim. Cheers

 

[Kaymo]

I guess rising damp is unusual or even impossible when the walls continue down well below ground level.

I'm not sure. Really depends. If for example the cellar has been tanked on the inside, which a lot of them are, dampness coming into the wall just below ground level can only go up and if it can't get out to the outside wall because of the concrete, it could go to the base of the inside of your ground floor room wall.

I found this crowd who supply it to be very helpful in terms of finding installers - https://www.ecologicalbuildingsystems.com/UK/Products/Product-Detail/Diasen-Thermal-Plaster - they put me in touch with a couple but both were far enough away that I would be paying for overnight accommodation. In theory any plasterer should be able to follow the instructions and use it, but the ones I talked to seemed a bit scared of trying something unfamiliar.

Personally I'd take my time and think it through. If the plaster is a real mess then I would understand, but it was typical that lime plaster was covered with wallpaper. When I took if off on that one wall and got down to stone I had to do some repairs and repoint the wall before starting to build back up.

Old stone walls that are thick and dry often have better u-values than you would expect, and the heat loss in old houses is often to do with draughts so that should be the first port if you haven't already done so.

 

[gomez500]

I'm not sure. Really depends. If for example the cellar has been tanked on the inside, which a lot of them are, dampness coming into the wall just below ground level can only go up and if it can't get out to the outside wall because of the concrete, it could go to the base of the inside of your ground floor room wall.

I found this crowd who supply it to be very helpful in terms of finding installers - https://www.ecologicalbuildingsystems.com/UK/Products/Product-Detail/Diasen-Thermal-Plaster - they put me in touch with a couple but both were far enough away that I would be paying for overnight accommodation. In theory any plasterer should be able to follow the instructions and use it, but the ones I talked to seemed a bit scared of trying something unfamiliar.

Personally I'd take my time and think it through. If the plaster is a real mess then I would understand, but it was typical that lime plaster was covered with wallpaper. When I took if off on that one wall and got down to stone I had to do some repairs and repoint the wall before starting to build back up.

Old stone walls that are thick and dry often have better u-values than you would expect, and the heat loss in old houses is often to do with draughts so that should be the first port if you haven't already done so.

I take all your points especially that about mass of old thick stone walls. The benefits may only be marginal for all the work necessary, some of which may be unknown once stripping the render. The lime render is in pretty good overall shape it's just too rough and undulating to be painted hence why the previous ppl stuck horrible unbreathable wallpaper all over it. I may well consider skimming with a breathable finish and applying some nice breathable paint. Maybe if the wall had some moisture in in, it will be warmer once that moisture has had a chance to get out.

 

[IT Minion]

That stuff sounds too good to be true. Which means it probably is too good to be true.

A quick search of the advertising material implies it has 5x the performance of PIR. (This references a R value of 2.25 and specifies (in a separate section) a depth of 10mm, roughly what you'd get from 50mm of PIR)
https://www.diasen.com/sp/en/p/diathonite-evolution.3sp

 

[IT Minion]

Ah, found it, the r value for 10mm is 0.222. So the numbers they seem to be quoting is 100mm or so of the stuff. Presumably 50mm inside and outside.

https://www.ecologicalbuildingsystems.com/docs/DIATHONITE EVOLUTION_Technical_Data_Sheet.output.pdf

If you put on 25mm on a building you'd be doing about as much as 12mm of celotex, which is pretty much pointless.

 

[Kaymo]

So the numbers they seem to be quoting is 100mm or so of the stuff. Presumably 50mm inside and outside.

No, it would just be 100mm on the outside, or the inside, you wouldn't put it on both.

If you put on 25mm on a building you'd be doing about as much as 12mm of celotex, which is pretty much pointless.

Except that you wouldn't, or shouldn't put celotex on an old building as it is impermeable. I wouldn't say it is pointless either, its actually the first 10mm or so of insulation that gives the biggest return, after that its always a law of diminishing returns. That being said, i'd agree if you are going to do it at all you'd be as well to do 50mm minimum, and ideally more than 100mm.

 

[IT Minion]

No, it would just be 100mm on the outside, or the inside, you wouldn't put it on both.


Except that you wouldn't, or shouldn't put celotex on an old building as it is impermeable. I wouldn't say it is pointless either, its actually the first 10mm or so of insulation that gives the biggest return, after that its always a law of diminishing returns. That being said, i'd agree if you are going to do it at all you'd be as well to do 50mm minimum, and ideally more than 100mm.

The brochure says to use it, and insulated plaster, on both sides of a wall to provide the required insulation levels.

How much is this stuff anyway? We are talking about applying it ten times as thick as it seems to refer, 36kg per square meter.

It just feels like a gimmick. Fine slather a bit on but it's not going to make much of a difference. Plus how much better is this than 100mm of any other sort of render?

Edit: the reason I reference celotex is that I have a rough idea of how that relates to insulation levels and think in those terms. For a period property I wouldn't know where to start on getting it close to modern spec insulation.

 

[Kaymo]

The brochure says to use it, and insulated plaster, on both sides of a wall to provide the required insulation levels.

Yes you are right. I forgot about that, but unless the house is a shell I couldn't see the point in having the disruption on both sides of the wall.

It just feels like a gimmick. Fine slather a bit on but it's not going to make much of a difference. Plus how much better is this than 100mm of any other sort of render?

Its not a gimmick, but whether it is the best choice depends on a number of factors. I worked out that a wall with a u value of 2.6 would reduce to about 1.2 with about 20-25mm of diathonite, and to about 0.34 with 100mm. So even 20mm or so would be more than a halving of heat loss. However, I also worked out that wood fibre board with lime render, for the same u value would be cheaper on materials. I'd say that what diathonite and similar renders have in their favour is that there is only one trade involved - a plasterer with a plastering machine can rattle this on without any other trades. Its ideal for old houses that have more natural contours. One of the concerns about it is that it is an Italian product, and what works in an Italian climate might not work here - bearing in mind that the main reason for a render where I live is to protect from driving wind and rain, and its not clear whether this would stand up to that over time.

For a period property I wouldn't know where to start on getting it close to modern spec insulation.

The problem is that it is nearly impossible to get a period property to modern spec, you can only do what you can. Its also nearly impossible to know what the current u value of a period property is, because we usually don't completely know what is in the walls, they are often designed to allow air to circulate, and you can't for example lift the walls to insulate the footings. However, 20-30mm of nearly any insulation would half the heat loss of most period walls, so something is better than nothing.

 

[loredana cornea]

I realize this post is old but it is among the top searches on google so I will provide some information in the hopes that it will be useful for others. I recently bought an old apartment, ground floor and since I am a huge fan of insulating everything, as ecologically and sustainable as I possibly can, I did a number on the apartment (p.s.: still working on it).
I chose to use:
* For the ceiling:
** 2 layers of Diathonite Evolution which was a mystery to apply at first...by trowel. I am not a builder who can afford a pump. It looks like dirt with bits of cork in it and it is very aerated and light. I bought 22 bags to cover about 100 sqm of ceiling @2cm thickness and I've just used a bit more than half and got a thickness of 3cm. So careful with the quantities. The second layer we learned has to be applied while the first layer is semi-wet because when it dries it becomes very hard and the new layer won't stick to it.
** ARGACEM HP coarse plaster - the stuff of dreams. 2 layers because the Diathonite will leave a very uneven area so you need something thick to cover it fully.
** Old House Store Supreme Ultra Fine - plaster mix made locally in Reading warehouse - I asked for the grain to be at max 0.5mm. It contains about 5% of matter with a bit of a bigger grain than that but it's no problem. It's used to restore old houses and it doesn't need any paint on it.

* For the walls:
** corkboard insulation from Mikewye - different thicknesses depending on the wall and how cold it was in each room (20, 40mm, 50mm, 60mm) + Isovit Ecork to apply the corkboards and to cover them, integrating a fiberglass mesh and cornerbeads
** Due to some delays in deliveries I used just in the kitchen a coat of ARGACEM HP coarse plaster (this material is simply impressive). I don't have enough words to describe and recommend it. It is easy to apply, it is grainy and off-white and has the feel of an old French house, very elegant. It prevents mold from forming, is breathable and you can just finish it with paint. Of course, I didn't do that because I'm me
** Due to the same delays in deliveries, I ended up using a lime plaster mix from a nearby company - Old House Store Supreme Ultra Fine - cost me £400 half a tonne.
** Last layer will be Stucco Fino from Mikewye. It is expensive but I bought the polishing soap and wax and hope to get a stone-like texture since this is Venetian Plaster. I just bought the white version but there are pigments to make it as you want.

* For the floor
** Again corkboard insulation from MikeWye @40mm thickness, then a woodflooring protective sheet and and natural bamboo flooring which was indeed more expensive than stratified flooring but half the price of hardwood flooring

I am very very happy with the choices