Limecrete or Concrete Floor

[bontwoody]

Hi

I’m in the process of renovating a solid stone wall house and am looking to replace the current quarry tile and earth floor with one that includes under floor heating.

My dilemma is with respect to do I use a limecrete or concrete slab. Ive been researching views on the web and through suppliers and I must say Im no clearer on the advantage of the limecrete over concrete (other than environmental issues).

As I understand things a limecrete floor is recommended in my situation to allow the building to breathe and reduce issues with rising damp caused by a DPM forcing out trapped moisture to the walls.

That all initially sounds reasonable but I’ve come across several views/facts that make me doubt this.

 

1. What is the process by which moisture is forced out to the walls? My personal thoughts are that the movement of moisture in the ground would occur from a high concentration moisture area to a low concentration moisture area and this would continue until all the ground has the same moisture level. It seems to me that the ground beneath a house would likely be less moist that that outside because it doesn’t get rained on. Surely then moisture would move in the opposite direction to that claimed? I suppose once the ground beneath the house had gotten moist and the outside had dried then the direction of movement would then change. There is also the issue that in Wales the subsoil is usually clay which does not allow water movement easily.

 

2. The advantage of using a limecrete slab and foamed glass base is that the moisture in the ground can permeate up and be released without reaching the walls. This would mean that any covering of the slab would have to be permeable too, such as limestone or clay pavers for example. However on enquiring at Ty-Mawr I got the following answer:

 

“For finishes that affect the breathability of the surface, the main consideration is ensuring the moisture from installing the slab has fully dried. The Glapor will stop any moisture reaching the slab from below so once the slab is dry any floor finish can be used.”

 

Surely if that answer is true, it negates the whole argument of a breathable floor and I might as well just use concrete with a DPM and foam insulation, which would ensure I could use any finish after a shorter wait time and have a better insulation value.

 

3. Old buildings always had permeable breathable floors. This is patently not true as many had slate floors, a substance so impermeable it was used as a damp proof course. The only way moisture could move through it would be through the mortared joints which would be a very small percentage of the surface area. Did this lead to increased problems in rising damp than say floors covered with clay tiles?

 

If anyone can help explain these apparent contradictions I would be grateful. Especially if there is any reliable research to back up views as opposed to anecdotal accounts.

 

Thanks Woody

 

[tonyshouse]

My view on moisture movement apart from flooding and spills is that moisture moves from places of high partial vapour pressure to places where the partial vapour pressure is lower. This is a downhill process, very basic. 
 

generally the pvp is higher indoors than outdoors especially if indoors is warmer than outdoors, the usual case. So moisture is trying to move from indoors to outdoors and from indoors into the substratas below the house.

 

I have a basement with no tanking 

 

so limecrete for me!  Heat will force moisture away but beware as the walls will be cold compared to a heated slab but even in the walls the pvp’s will be higher in the wall than outside. 

[jayc89]

Limecrete would be the purist's view. When we had a similar dilemma with our solid-brick house, we spoke with a range of people, including quite a few local builders who have done a fair few barn conversations. They said we'd be safe with a concrete slab and DPM providing there were no existing damp conditions (i.e. broken drains, external floor level build up etc). Nearly 12 months on and no problems yet...

 

Anecdotally, my grandparents house (also solid brick) had a concrete slab laid, with a liquid DPM, nearly 60 years ago now and it's still going strong. We came across the original quote a few weeks ago - check out that price!

 

Edited April 23, 2022 by jayc89

[SteamyTea]

PV/T=C.

Trouble is when looking at this, phase changes happen: sometimes simultaneously.

This means that V and C is also changing.

So.

𝛿P/𝛿T X 𝛿V/𝛿T = 𝛿C/𝛿T 

Or in English, as the pressure changes due to the temperature change, and the volume changes due to the temperature change, their product is equal to the change in the constant at those temperatures.

This can be simplified to.

 

(𝛿P 𝛿V)/𝛿T = C, where C is a variable for any given value of T.

We can thank Leibniz for the above. Differential Calculous is the underpinnings of nature.

 

Or just use cement based concrete, at least you will know that bit will set hard.

[bontwoody]

Thanks for the replies.

 

tonyshouse - I hadnt really considered the high moisture content in the internal air. My intention was (whichever floor I go for) to internally insulate the walls, probably with a timber frame and breathable insulation

 

jayc89 - I havent checked the existing wall condition yet as its hidden behind foiled backed plasterboard, but  I was going to address any obvious problems and maybe insert a french drain outside. I doubt Ill be able to get any builders to match that quote somehow 🙂. Good to see the basics were the same back then with the exception of the insulation layer!

 

SteamyTea - its been a while since any differenntial calculus was required of me, so thanks for the summary at the end. 🙂 The last time I was interested in phase change it was with respect to filling my thermal store with paraffin wax, which still sounds like a good idea if I had the balls to try it!

[SteamyTea]

7 minutes ago, bontwoody said:

The last time I was interested in phase change it was with respect to filling my thermal store with paraffin wax, which still sounds like a good idea if I had the balls to try it!

Why not use the latent heat of fusion in the refrigerant gas in a heat pump as a better option.  They come in a box, all ready to go, and integrate well with standard domestic plumbing.

The trouble with using paraffin wax is not the ~150 kJ/kg of storage between 48 and 68°C, it is stopping and starting the process in a controllable way.

Liquid water on the other had, may only have 4.18 kJ/kg, but is very controllable between 0 and 100°C, well actually a little higher and lower to be useful.

It is very cheap as well, so cheap that in the most expensive region to buy it in the UK, you can get 1 tonne of it for £8.

[bontwoody]

57 minutes ago, SteamyTea said:

It is very cheap as well, so cheap that in the most expensive region to buy it in the UK, you can get 1 tonne of it for £8.

I can get it cheaper than that from my rainwater tank 🙂

 

After much consideration about Legionella cycles, I think I will be going for a pressurised cylinder in my new house rather than a thermal store. But thats another debate 🙂

[jfb]

I had a similar conundrum for my renovation. In the end I went for EPS/concrete throughout and it has worked fine for me.

Only slight downside has been a little bit of salts/discolouration on a couple of sections of render near the floor.

My building wasn't particularly damp to start with if that is relevant. And it is combined with woodfibre/breathable wall insulation.

 

 

[Roger440]

7 hours ago, bontwoody said:

Thanks for the replies.

 

tonyshouse - I hadnt really considered the high moisture content in the internal air. My intention was (whichever floor I go for) to internally insulate the walls, probably with a timber frame and breathable insulation

 

jayc89 - I havent checked the existing wall condition yet as its hidden behind foiled backed plasterboard, but  I was going to address any obvious problems and maybe insert a french drain outside. I doubt Ill be able to get any builders to match that quote somehow 🙂. Good to see the basics were the same back then with the exception of the insulation layer!

 

SteamyTea - its been a while since any differenntial calculus was required of me, so thanks for the summary at the end. 🙂 The last time I was interested in phase change it was with respect to filling my thermal store with paraffin wax, which still sounds like a good idea if I had the balls to try it!

 

I think you need to establish whats going on with the walls as well before making decisions.

 

As ive posted before, i started with the issue of wet walls, properly wet, enough to rot the socket back boxes. House (well front part)  is mid 1800's, no DPC, brick. humidity usually around 90%

 

There were issues. The 2 obvious ones were high external ground level on the gable end, and an uncapped chimney. They were easily fixed.

 

Externally, below the render, it was pointed in cement. Removed and redone with lime. Externally things improved.

 

Following a visit by the river, was the push i needed to strip of the gypsum plaster. Having done that, again the wall dried but it remained damp above the floor.

 

Floor was concrete on a plastic dpm. After some months and things improving no further, i decided time for a lime floor.

 

So up it came. 

 

The effect was, frankly more pronounced that i could have hoped for. In the end i had no floor for a few months. Dried out completely. The walls and the soil. Ended up like a dust bowl!

 

So why am i rambling on? Because, for me, it was obvious that the concrete slab was the issue that was driving the moisture to the walls. Which couldnt lose the moisture effectively.

 

As you say, lots of conflicting info. Im working on what i see with my own eyes. 

 

The lime floor, on foamed glass, has been down since early Jan. No issues to date. Humidity spiked when the floor went in but now down to 50%

 

No signs of damp in the walls. Granted its maybe a bit early to be 100% confident. But im reasonably confident.

 

The real issue with making the decision is that to really understand whats going on means living with it for a while. For me that was no issue, but that doesnt work for most. Plus every case will be different. Some will get away with a concrete floor. Some wont. In my case it was pretty clear. But, why would you take the risk of concrete, other than cost? 

 

One advantage of the glass/lime was less excavation next to walls with bugger all foundation as the glass is also doing job of the sub base. Total depth from top of floor to soil, 225mm.

 

Of course, if the house was damp even "as built" then of course rectifying later inappropiate materials isnt going to fix it anyway!

 

No easy answers! Unless you are really keen and retrofit a dpc to the walls. Though thats probably only sensible if its brick with straight course. Old building walls id guess is stone?

 

 

 

[Roger440]

5 hours ago, jfb said:

I had a similar conundrum for my renovation. In the end I went for EPS/concrete throughout and it has worked fine for me.

Only slight downside has been a little bit of salts/discolouration on a couple of sections of render near the floor.

My building wasn't particularly damp to start with if that is relevant. And it is combined with woodfibre/breathable wall insulation.

 

 

 

Hmmm. Bit of a contradiction? Worked fine, but have salts and discolouration. 

 

My conclusion i think would be different from yours on the fine bit.

[bontwoody]

16 hours ago, jfb said:

I had a similar conundrum for my renovation. In the end I went for EPS/concrete throughout and it has worked fine for me.

Only slight downside has been a little bit of salts/discolouration on a couple of sections of render near the floor.

My building wasn't particularly damp to start with if that is relevant. And it is combined with woodfibre/breathable wall insulation.

 

 

Thanks for the reply and it probably is relevent regarding the starting conditions of the walls. When you say discolouration of the render do you mean the internal plaster on the face of the wall insulation? Is the wall insulation stuck to the wall or is there a stud wall and cavity? Thanks

[bontwoody]

11 hours ago, Roger440 said:

 

The real issue with making the decision is that to really understand whats going on means living with it for a while. For me that was no issue, but that doesnt work for most. Plus every case will be different. Some will get away with a concrete floor. Some wont. In my case it was pretty clear. But, why would you take the risk of concrete, other than cost? 

 

One advantage of the glass/lime was less excavation next to walls with bugger all foundation as the glass is also doing job of the sub base. Total depth from top of floor to soil, 225mm.

 

 

I dont really have the luxury of living with it as we will need to get a better heating system in before the winter. Cost is one issue to consider but also being able to get someone with the right skills quickly. Its a good point regarding the excation depth and I wont know about that until Ive managed to dig a few inspection pits. Out of curiousity what floor covering do you have over the limecrete? Thanks for taking the time to write a comprehensive reply 🙂

[bontwoody]

Doing some further research this morning I found this link, which has a DPM and polished concrete floor above the foamed glass sub-floor. Is it then that the free draining sub-floor is more important than the limecrete slab in preventing damp?

https://www.womersleys.co.uk/Guides/Insulated Floors Case Study Aisled Barn.pdf

[jfb]

2 hours ago, bontwoody said:

Thanks for the reply and it probably is relevent regarding the starting conditions of the walls. When you say discolouration of the render do you mean the internal plaster on the face of the wall insulation? Is the wall insulation stuck to the wall or is there a stud wall and cavity? Thanks

Yes the internal render on woodfibre insulation boards (render behind the boards as airtight layer, boards fixed with no gap, then rendered on top)

[jfb]

13 hours ago, Roger440 said:

 

Hmmm. Bit of a contradiction? Worked fine, but have salts and discolouration. 

 

My conclusion i think would be different from yours on the fine bit.

Well I guess that depends on how much it matters to you.

[jfb]

59 minutes ago, bontwoody said:

Doing some further research this morning I found this link, which has a DPM and polished concrete floor above the foamed glass sub-floor. Is it then that the free draining sub-floor is more important than the limecrete slab in preventing damp?

https://www.womersleys.co.uk/Guides/Insulated Floors Case Study Aisled Barn.pdf

Seems interesting and well thought out. Be interesting to know how many land drain pipes they have coming out through the foundations and where it all goes.

I'd also like to know the u value of the 250mm expanded glass - can't remember off hand what it equates to but I suspect not nearly as good as a similar thickness of EPS (and they also have a 100mm layer of sub base above the expanded glass to warm up)

[bontwoody]

3 hours ago, jfb said:

I'd also like to know the u value of the 250mm expanded glass - can't remember off hand what it equates to but I suspect not nearly as good as a similar thickness of EPS (and they also have a 100mm layer of sub base above the expanded glass to warm up)

Well they also included 75mm of polyurethane insulation above the 250mm of foam glass so together that sounds pretty good. I guess there would be no issues in using 50mm of liquid screed instead of 100mm of concrete if you wanted less thermal mass and quicker response times.

[Roger440]

On 24/04/2022 at 09:56, bontwoody said:

 

I dont really have the luxury of living with it as we will need to get a better heating system in before the winter. Cost is one issue to consider but also being able to get someone with the right skills quickly. Its a good point regarding the excation depth and I wont know about that until Ive managed to dig a few inspection pits. Out of curiousity what floor covering do you have over the limecrete? Thanks for taking the time to write a comprehensive reply 🙂

 

I have used limestone tiles. Pointed up with lime mortar.

 

Without time on your sude i would view the limecrete as a "safer" option. 

 

Concrete might be ok, but might not be. Limecrete will give you the best chance. It is more expensive though.

[Roger440]

On 24/04/2022 at 12:48, jfb said:

Well I guess that depends on how much it matters to you.

 

The early signs od damp would definitely concern. me. Its pretty much the only reason the salets would be coming through.

 

Id take a guess and say the wall itself will be damp were you to check.

[bontwoody]

26 minutes ago, Roger440 said:

 

I have used limestone tiles. Pointed up with lime mortar.

 

Without time on your sude i would view the limecrete as a "safer" option. 

 

Concrete might be ok, but might not be. Limecrete will give you the best chance. It is more expensive though.

Thanks Roger