Could the new studies about limecrete mean underfloor Celotex (PIR) is alright?

[DampedOut]

There's been recent studies that say that limecrete isn't that breathable and that the benefits in limecrete systems are coming from the foamed glass aggregate used under limecrete [1]. And, more to the point, that impermeable floors don't affect the walls [2]. Could that possibly mean we can get away with ignoring cement slabs and even using non-breathable insulation on top of them?

I'm looking at a room where I could actually meet building regs for underfloor insulation if I used Celotex over the existing cement slab. Exterior ground level would be a little lower than the slab or equal to it. I could even add an effective electric underfloor heating system if I used Celotex.

I'm toying with this idea: cement slab + Celotex + electric UFH + pamments. I'm a bit worried about moisture damaging the PIR, in which case, maybe that layer would have a wood fibre border against the external wall. What am I missing here? Why are these terrible ideas?

[1] https://www.rilem.net/publication/publication/527?id_papier=12862
[2] https://researchportal.bath.ac.uk/e...-of-wall-moisture-in-a-historic-building-in-r
Cited originally in another thread

 

[Toby Newell]

There's been recent studies that say that limecrete isn't that breathable and that the benefits in limecrete systems are coming from the foamed glass aggregate used under limecrete [1]. And, more to the point, that impermeable floors don't affect the walls [2]. Could that possibly mean we can get away with ignoring cement slabs and even using non-breathable insulation on top of them?

I'm looking at a room where I could actually meet building regs for underfloor insulation if I used Celotex over the existing cement slab. Exterior ground level would be a little lower than the slab or equal to it. I could even add an effective electric underfloor heating system if I used Celotex.

I'm toying with this idea: cement slab + Celotex + electric UFH + pamments. I'm a bit worried about moisture damaging the PIR, in which case, maybe that layer would have a wood fibre border against the external wall. What am I missing here? Why are these terrible ideas?

[1] https://www.rilem.net/publication/publication/527?id_papier=12862
[2] https://researchportal.bath.ac.uk/e...-of-wall-moisture-in-a-historic-building-in-r
Cited originally in another thread

Interesting. That was my theory. Yes and No. Limecrete is called limecrete because of green washing, and it sounds sexy. It's not very breathable but it's slightly better than concrete and damp issues are cumulative, 10% here, 20% there, all the factors add up. Recycled foamed glass or lightweight fired clay-crete doesn't sound as sexy hence the focus on the word 'lime'. Extra strong NHL5 at 1:3 is similarly breathable to Portland concrete at 1:8. NHL5 at 1:8 is around 5 to 20% more breathable than concrete at 1:8. So, it would appear that a weaker concrete cement mix would have similar properties to a strong NHL5. Well, again, yes and again, no.

Not many studies and not real world, all done in lab on small samples, NEDC emissions test anyone...?

A strong NHL5 may only be maginally more breathable in the lab but some research suggests it's sorptivity is up to 50% higher. Also read the details... the study authors of some studies have provided consultancy to Blue Circle and Hanson Bricks...ahem... this is actually quite normal in research, but there may or may not be a conflict of interest when the countries leading cement manufacturer Blue Circle (that is owned by the worlds largest cement manufacturer, Lafarge ) is paying for some of your grants and some of your research suggests that cement is as good as lime...

In real world use then it is highly likely that even strong NHL5 transfers moisture considerably better than a weak portland cement, albeit far, far less than a non hydraulic lime. But again, that isn't really the issue. You are correct, it is the foamed glass that is doing the heavy lifting here by increasing the insulation of the slab = higher surface temps = less condensation. Again, you are correct that a similar thickness of PIR under NHL5 or concrete would probably offer more insulation as it has a lower k value but you are missing one vital component, drainage.

Water from the surrounding earth and walls can easily drain through foamed glass, not so much through PIR. So I think that would be the main issue.

In your case the issue is that your insulation is on the warm side ie on top. Your concrete slab is going to condense water under your cellotex / PIR. Any insulation and UFH is good. If you put cellotex EPS/ PIR under a concrete slab that would be better, then you are only losing out on the drainage effect.

EPS / PIR absorb water over time and thus their k value will rise, whereas foamed glass retains it's albeit lower insulative properties over time.

I guess limecrete with foamed glass / fired clay is the best system, but pretty moot if you don't have the sponds, just do what you can.

I don't see that any of your ideas are terrible. I am presuming that by 'wood fibre board' you mean 'wood fibre cement board', ie the stuff you lime plaster to. The shredded wheat type stuff? In that case it's pretty water resistant but not waterproof, especially where cut and I would think much less waterproof than both EPS and PIR. So, I don't see the advantage. But then, I am mostly basing that on anecdotal evidence that I've seen a lot of EPS hot beverage cups, yet, to date, not one made out of wood fibre board.

 

[Toby Newell]

There's been recent studies that say that limecrete isn't that breathable and that the benefits in limecrete systems are coming from the foamed glass aggregate used under limecrete [1]. And, more to the point, that impermeable floors don't affect the walls [2]. Could that possibly mean we can get away with ignoring cement slabs and even using non-breathable insulation on top of them?

I'm looking at a room where I could actually meet building regs for underfloor insulation if I used Celotex over the existing cement slab. Exterior ground level would be a little lower than the slab or equal to it. I could even add an effective electric underfloor heating system if I used Celotex.

I'm toying with this idea: cement slab + Celotex + electric UFH + pamments. I'm a bit worried about moisture damaging the PIR, in which case, maybe that layer would have a wood fibre border against the external wall. What am I missing here? Why are these terrible ideas?

[1] https://www.rilem.net/publication/publication/527?id_papier=12862
[2] https://researchportal.bath.ac.uk/e...-of-wall-moisture-in-a-historic-building-in-r
Cited originally in another thread

Not being a troll, just trying to be helpful, citation 1 is behind a paywall so we cannot see what 'slightly more permeable' means and what binder:aggregate ratios were compared.

Did you read citation 2?

The wall they chose (in Wales where it is quite rainy) was North facing, ie possibly the driest I think it would of been better if they had compared a South or West facing elevation, better still all four! To see if the results were the same for the elevations exposed to more precipitation. The study also says the wall was a 600mm thick rubble and cement wall with painted cement render to the exterior... double Sooo... they measured the driest wall that was rendered in non breathable cement, which was painted. I quote 'The wall was rough cast cement rendered and painted on the external face' Hmmmm. I would of liked to have seen them spend 3 years on all 4 cardinal elevations and on walls which were both cement rendered and painted AND walls that were lime rendered and unpainted. Ie walls that were actually breathable

3 years is a long time to wait to present results that a 600mm thick rubble wall that is coated in two layers of (possibly) impermeable materials, doesn't transfer water that well. Irrespective of how you fiddled with the floor. Maybe the results on a SW facing lime rendered wall without any cement render or paint that receives a lot more driven rain would of been the same, maybe not. Seems like a missed opportunity to me to spend 3 years on a study with seemingly serious confounding factors. Tbh, I didn't read what their control reference was, if any, maybe they accounted for that, on the face of it it seems meaningless to me.

Now, I only undertook 6 months materials science research in a lab but at least they wrote to me and said they decided to take out a limited world wide patent on the back of the part I worked on, which was nice. Shame I had to sign an NDA (actually The Official Secrets Act as the clients weremulti national) so I couldn't go and sell it I'm not sure the dudes in Bath got the same response. I could be being totally thick (and lazy by not reading it all the way through) but it seems to me, that their research was not very well thought out.

I think I am well known for being incredibly sceptical of greenwashing but really I just don't like misinformation on either side. It would be nice if they could come up with a cheaper solution, I think better research is needed.

I hope you find an economical and workable solution.

 

[aockenden]

Is there a consensus that NHL 5 is even necessary for a lime slab? I have been wondering about using NHL 3.5 instead to get additional breathability. Surely, 3 to 1 (sharp, well-graded building sand to NHL 3.5) laid a few inches thick, sitting on top of a properly COMPACTED foam-glass base, and covered with a layer of hard-wearing tiles / slates / flagstones would be enough to support typical non-structural weight-loads (humans, furniture, partition / stud walls, etc.)???

 

[Lacan07]

There's been recent studies that say that limecrete isn't that breathable and that the benefits in limecrete systems are coming from the foamed glass aggregate used under limecrete [1]. And, more to the point, that impermeable floors don't affect the walls [2]. Could that possibly mean we can get away with ignoring cement slabs and even using non-breathable insulation on top of them?

I'm looking at a room where I could actually meet building regs for underfloor insulation if I used Celotex over the existing cement slab. Exterior ground level would be a little lower than the slab or equal to it. I could even add an effective electric underfloor heating system if I used Celotex.

I'm toying with this idea: cement slab + Celotex + electric UFH + pamments. I'm a bit worried about moisture damaging the PIR, in which case, maybe that layer would have a wood fibre border against the external wall. What am I missing here? Why are these terrible ideas?

[1] https://www.rilem.net/publication/publication/527?id_papier=12862
[2] https://researchportal.bath.ac.uk/e...-of-wall-moisture-in-a-historic-building-in-r
Cited originally in another thread

I wouldn't use limcrete or cement, never been a fan of any solid flooring unless its on a new build and was installed as the walls were going up.

 

[DampedOut]

Not being a troll, just trying to be helpful, citation 1 is behind a paywall so we cannot see what 'slightly more permeable' means and what binder:aggregate ratios were compared.

No worries, I didn't take it that way

The wall they chose (in Wales where it is quite rainy) was North facing, ie possibly the driest I think it would of been better if they had compared a South or West facing elevation, better still all four! To see if the results were the same for the elevations exposed to more precipitation. The study also says the wall was a 600mm thick rubble and cement wall with painted cement render to the exterior... double Sooo... they measured the driest wall that was rendered in non breathable cement, which was painted. I quote 'The wall was rough cast cement rendered and painted on the external face' Hmmmm. I would of liked to have seen them spend 3 years on all 4 cardinal elevations and on walls which were both cement rendered and painted AND walls that were lime rendered and unpainted. Ie walls that were actually breathable

You make some fair points, for sure! To play devil's advocate, I wonder if they did it this way to control for certain factors. They seem to have set out to prove that unbreathable floors don't drive moisture up the rubble walls.

It makes sense to me that for that test, they'd put the probes and dowels on the inside of the test wall and then try to limit a few other factors. Maybe that explains why a north-facing wall? —> less sun hitting the wall, less sunlight hours overall so less absolute variation from winter to summer, and less driven rain pushing moisture into the wall. All that might mean that the moisture readings you get are mostly going to be caused by moisture coming from inside the building. It'd be nice if they explained their logic in those choices.

I also don't like greenwashing for what it's worth. (We deserve better and it undermines the real need.) The biggest issue I have these days is that building regulations are a one-size-fits-all system and no one is subsidising aerogel. For the life of me I can't find proper data about underfloor heating's effectiveness with different insulation or even u-values because everyone defaults to "building regs say x". What can you do in that situation?

I am wondering about if I do this with PIR how to direct moisture that collects under the PIR towards the outer wall and out. With clothing you can get directional wicking, but I don't know which – if any – membrane can do that kind of thing. :/


p.s. I mean, I should probably share that this whole thing started as a thought experiment for me. I have a big spreadsheet with the R-values and U-values of different materials at different thicknesses. I worked out that building regs for floors (.25 W/m2K) is an R-value of 4. And then 100mm of PIR will give you an R-value of 4.55. Wood fibre doesn't even come close, it's 2.70 and Glapor is 1.20. So I began to wonder... well... is there a way to use PIR after all?

 

[DampedOut]

There's also a cork insulating limecrete I was looking at to try to squeeze precious R-value decimals out of. I think it may be NHL 5 (honestly no clue).

I'll give them points for the woman dancing with a long red veil on the webpage. Nothing makes me think of insulating limecrete as much as women dancing dramatically with veils. It feels very 90s "Gillette ad".

 

[Toby Newell]

Is there a consensus that NHL 5 is even necessary for a lime slab? I have been wondering about using NHL 3.5 instead to get additional breathability. Surely, 3 to 1 (sharp, well-graded building sand to NHL 3.5) laid a few inches thick, sitting on top of a properly COMPACTED foam-glass base, and covered with a layer of hard-wearing tiles / slates / flagstones would be enough to support typical non-structural weight-loads (humans, furniture, partition / stud walls, etc.)???

Yes, I think that is the issue, even NHL5 at 1:2 which I think might be the strongest mix is still considerably weaker than concrete.

 

[Toby Newell]

There's also a cork insulating limecrete I was looking at to try to squeeze precious R-value decimals out of. I think it may be NHL 5 (honestly no clue).

I'll give them points for the woman dancing with a long red veil on the webpage. Nothing makes me think of insulating limecrete as much as women dancing dramatically with veils. It feels very 90s "Gillette ad".

I think they use fired clay aggregate in the limecrete already which is a clay foamed glass analogue. I think clay probably binds better to NHL5 as it is up to 25% clay by weight already.

 

[aockenden]

I think they use fired clay aggregate in the limecrete already which is a clay foamed glass analogue. I think clay probably binds better to NHL5 as it is up to 25% clay by weight already.

Yeah the thing that makes me nervous about the lightweight expanded clay aggregate (LECA balls) is that because they are round and relatively smooth they can’t really be compacted with a whacker-plate or whatever. Idk what that does to the compressive strength of the entire flooring system.

 

[Toby Newell]

No worries, I didn't take it that way

You make some fair points, for sure! To play devil's advocate, I wonder if they did it this way to control for certain factors. They seem to have set out to prove that unbreathable floors don't drive moisture up the rubble walls.

It makes sense to me that for that test, they'd put the probes and dowels on the inside of the test wall and then try to limit a few other factors. Maybe that explains why a north-facing wall? —> less sun hitting the wall, less sunlight hours overall so less absolute variation from winter to summer, and less driven rain pushing moisture into the wall. All that might mean that the moisture readings you get are mostly going to be caused by moisture coming from inside the building. It'd be nice if they explained their logic in those choices.

I also don't like greenwashing for what it's worth. (We deserve better and it undermines the real need.) The biggest issue I have these days is that building regulations are a one-size-fits-all system and no one is subsidising aerogel. For the life of me I can't find proper data about underfloor heating's effectiveness with different insulation because everyone defaults to "building regs say x". What can you do in that situation?

I am wondering about if I do this with PIR how to direct moisture that collects under the PIR towards the outer wall and out. With clothing you can get directional wicking, but I don't know which – if any – membrane can do that kind of thing. :/


p.s. I mean, I should probably share that this whole thing started as a thought experiment for me. I have a big spreadsheet with the R-values and U-values of different materials at different thicknesses. I worked out that building regs for floors (.25 W/m2K) is an R-value of 4. And then 10mm of PIR will give you an R-value of 4.55. Wood fibre doesn't even come close, it's 2.70 and Glamor is 1.20. So I began to wonder... well... is there a way to use PIR after all?

From someone who has worked and studied in labs this does not make sense. If you want to isolate all external real world factors then why conduct the experiment on a house? Surely creating a small bit of wall and floor in a lab would be better? Zero sun, zero rain! Much easier to control.

The issue is in the real world multiple factors affect moisture transport. Heat flows from hot > cold, liquid moisture goes from higher humidity > lower humidity, depending on the pressure. Pressure of liquid or gas goes from higher vapour pressure to lower vapour pressure. Whether the wall outside is wet, whether it is breathable affects the rate of moisture transport, as does heat. There are so many interracting variables you would need to already have created a viable, experimentally proven model and have coded that into a super computer. This experiment doesn't tell us anything about how slabs and walls interract in a general real world model. It is literally 3 years of navel gazing. All this experiment shows us is that if you have a cement rendered, painted 600mm rubble wall and a tarp covered floor that this will happen.

 

[aockenden]

Yes, I think that is the issue, even NHL5 at 1:2 which I think might be the strongest mix is still considerably weaker than concrete.

I might volunteer to be the Guinea pig and see if NHL 3.5 is strong enough for a lime slab.

 

[Toby Newell]

^^^ That's why it would of been better to take measurements on all 4 walls, with different rain, wind and sun exposure. And also to conduct experiments on houses with no cenent render.

Actually, the best data would be taken from a house where you could have half of each wall rendered abd painted and half lime pointed. That way you could compare the difference in moisture transport.

 

[Toby Newell]

I might volunteer to be the Guinea pig and see if NHL 3.5 is strong enough for a lime slab.

I guess some type of fibre could help with micro cracking. I think the issue is with building regs. Building control is going to specify some sort of minimum strength limit. I am guessing this is a one size fits all and that some smaller structures could get away with a lower strength slab.

 

[aockenden]

I guess some type of fibre could help with micro cracking. I think the issue is with building regs. Building control is going to specify some sort of minimum strength limit. I am guessing this is a one size fits all and that some smaller structures could get away with a lower strength slab.

Yes the fiber sounds like a good idea.

 

[Toby Newell]

No worries, I didn't take it that way

You make some fair points, for sure! To play devil's advocate, I wonder if they did it this way to control for certain factors. They seem to have set out to prove that unbreathable floors don't drive moisture up the rubble walls.

It makes sense to me that for that test, they'd put the probes and dowels on the inside of the test wall and then try to limit a few other factors. Maybe that explains why a north-facing wall? —> less sun hitting the wall, less sunlight hours overall so less absolute variation from winter to summer, and less driven rain pushing moisture into the wall. All that might mean that the moisture readings you get are mostly going to be caused by moisture coming from inside the building. It'd be nice if they explained their logic in those choices.

I also don't like greenwashing for what it's worth. (We deserve better and it undermines the real need.) The biggest issue I have these days is that building regulations are a one-size-fits-all system and no one is subsidising aerogel. For the life of me I can't find proper data about underfloor heating's effectiveness with different insulation or even u-values because everyone defaults to "building regs say x". What can you do in that situation?

I am wondering about if I do this with PIR how to direct moisture that collects under the PIR towards the outer wall and out. With clothing you can get directional wicking, but I don't know which – if any – membrane can do that kind of thing. :/


p.s. I mean, I should probably share that this whole thing started as a thought experiment for me. I have a big spreadsheet with the R-values and U-values of different materials at different thicknesses. I worked out that building regs for floors (.25 W/m2K) is an R-value of 4. And then 100mm of PIR will give you an R-value of 4.55. Wood fibre doesn't even come close, it's 2.70 and Glapor is 1.20. So I began to wonder... well... is there a way to use PIR after all?

For example.... a non rendered breathable wall will allow more moisture to evaporate at the exterior surface, this creates a lower vapour pressure that draws moisture up from the ground and insude the wall. But. It will also absorb more moisture from the outside environment, how do these competing factors affect the moisture transport from the slab? Moisture will only move from the slab if the wall is less wet! If the wall is saturated and the slab is not, moisture will flow in the reverse direction! The experiment is silly. I would say that all it does is create a postulate, from which the scientists could possibly create a theory, and then devise an experiment to test that. On it's own it appears meaningless to me.

 

[Kearn]

I might volunteer to be the Guinea pig and see if NHL 3.5 is strong enough for a lime slab.

We’re using a relatively weak 3.5:1 mix of 3.5 for rebuilding our plinth walls… they have far more work to do than a floor for furniture and paws!

 

[Toby Newell]

We’re using a relatively weak 3.5:1 mix of 3.5 for rebuilding our plinth walls… they have far more work to do than a floor for furniture and paws!

View attachment 13440

Wow. That looks scary.

 

[Kearn]

Wow. That looks scary.

The joys of heartwood rot from the underside of the sole plate - nice combo of external cement fillets overlapping the timber and trapping water in and under and the hideous repointing of the plinth in the devils own mix external and internally…

 

[Toby Newell]

The joys of heartwood rot from the underside of the sole plate - nice combo of external cement fillets overlapping the timber and trapping water in and under and the hideous repointing of the plinth in the devils own mix external and internally…

That would do it.