easy question this time on my very steep learning curve. On the new limecrete floor how do I lay floor slabs? Do I mix a lime mortar mix and bed them in? I do not want to seal the floor to enable the all important breathability. It has UFH - well will have - eventually!
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livias
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Yes. And grout in lime too ☺
JanJonWestWales
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For the bed, I used NHL5 for maximum strength with some breathability
For the grout I used 3.5 for max breathability throught the gaps,
If you find the grout too soft and rubs away, then dig it out and use NHL5
J
For the grout I used 3.5 for max breathability throught the gaps,
If you find the grout too soft and rubs away, then dig it out and use NHL5
J
Flyfisher
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Why is strength really such a consideration? If the sub base is well prepared and compacted then the slabs are not going to move downwards and assuming they are constrained from moving sideways by the walls there's no real strength needed laterally either.
I'd be happy to use NHL2.
I'd be happy to use NHL2.
livias
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We used 3.5 for both as we had it
Flyfisher
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That's fair enough, but the OP was about maintaining the 'all important breathability', in which case wouldn't NHL2 be the best option?
On the other hand, I wonder what mix was used for the limecrete floor slab? If it was, for example, NHL5 then using a more breathable bedding/grouting mix on top is not going to improve breathability.
On the other hand, I wonder what mix was used for the limecrete floor slab? If it was, for example, NHL5 then using a more breathable bedding/grouting mix on top is not going to improve breathability.
Thank you for the responses. Next part of the question is will the slate floor slabs stay in place bedded on the lime mortar with the underfloor heating? The slate supplier indicated that he thought there would be issues with the slate not sticking if laid as I had suggested. He advised I speak to the 'glue' man. I guess on a concrete floor slab with UFH a tile adhesive would be used?
So for those who have UFH under a limecrete slab and slate slabs on top, does anything move?
So for those who have UFH under a limecrete slab and slate slabs on top, does anything move?
Flyfisher
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We have 40m2 of tiled floor with UFH, though it's in a new extension so it has a concrete sub base except for a border of about 0.5m limecrete where it abuts the original house. On top of that is 100m of celotex-type insulation on which the UFH pipework is laid and on top of that is a 50mm cement screed, except for the 0.5m border with the house.
We then covered the floor with new pamments (Norfolk Pamments Company), which we laid in a lime mortar mix and grouted with the same mix. This was before I started using mainly NHL2 and I think the mix was 9:3:1 of sharp sand, hydrated lime and white cement.
Having never experienced UFH I was a little apprehensive about whether the tiles or grouting might crack or move with thermal expansion/contraction but so far we've had no problems at all (about four years now).
I don't know if slate tiles will behave any differently though I can't really see why they should. If they are well-bedded then where will any 'lifting' forces come from? It's not as if they will float away if they're not stuck down :wink: Besides, there are plenty of old tiled floors laid directly on earth - indeed we have one in another room and the tiles are rock solid (no UFH though).
I can understand your supplier being reticent though. They probably only ever stick the things down with modern adhesives and you're asking them about doing something they (probably) have no experience about, so I would expect them to play safe.
We then covered the floor with new pamments (Norfolk Pamments Company), which we laid in a lime mortar mix and grouted with the same mix. This was before I started using mainly NHL2 and I think the mix was 9:3:1 of sharp sand, hydrated lime and white cement.
Having never experienced UFH I was a little apprehensive about whether the tiles or grouting might crack or move with thermal expansion/contraction but so far we've had no problems at all (about four years now).
I don't know if slate tiles will behave any differently though I can't really see why they should. If they are well-bedded then where will any 'lifting' forces come from? It's not as if they will float away if they're not stuck down :wink: Besides, there are plenty of old tiled floors laid directly on earth - indeed we have one in another room and the tiles are rock solid (no UFH though).
I can understand your supplier being reticent though. They probably only ever stick the things down with modern adhesives and you're asking them about doing something they (probably) have no experience about, so I would expect them to play safe.
livias
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Any movement problems on our floor (ufh, limecrete and mexican terracotta tile) appeared very quickly and were due to inadequate tamping down in the first place. Anyhow it was only a couple of tiles so we just reset them. There does not seem to be any problem in general
skier-hughes
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I've been told by two well experienced lime contractors that the breath-ability of nhl2/3.5/5 is just the same, it is the speed at which it will set to and the strength it has at any given point that is different.
Flyfisher
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skier-hughes said:
First time I've heard that. I've read that breathability also varies across the different types of lime. I've not searched exhaustively but couldn't find any references to support equal breathability but lots to support variable breathability, eg http://thenaturalbuildingcentre.co.uk/lime/wp-content/uploads/2013/09/Choosing-a-Lime-20101.pdf
MatthewC
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I used NHL 5 for my limescrete floor and laid an electric UFH system under the 50 mm screed which was the bed for the limestone flags. However, apart from testing it, I have not used my UFH at all, as the floor is always so warm without it. I think this could be due to using a 200mm layer of LECA under the 100mm slab of NHL5 and LECA.
It's been over six years now without any problem and I still think the floor is great. However if I did it again (and I might yet do my hall) I would probably use the alternative foam glass aggregate instead of LECA, as you can tamp that more.
Matthew
(see my blog http://houseintheenchantedforest.blogspot.co.uk/2011/04/fitting-limecrete-floor-part-1.html and later entries for more details on what we did here)
It's been over six years now without any problem and I still think the floor is great. However if I did it again (and I might yet do my hall) I would probably use the alternative foam glass aggregate instead of LECA, as you can tamp that more.
Matthew
(see my blog http://houseintheenchantedforest.blogspot.co.uk/2011/04/fitting-limecrete-floor-part-1.html and later entries for more details on what we did here)
skier-hughes
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I don't know why, I've said it many timesFlyfisher said:
Flyfisher
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Must be my ageing memory :lol:
Seriously though, there must be a definitive answer somewhere . . . but where?
Seriously though, there must be a definitive answer somewhere . . . but where?
Getting mixed messages. I spoke to the glue man and he told me his water based synthetic latex polymer would be breathable because I was using it in a diluted form, followed by their cementitious adhesive with polymer technology would all be ok and the floor slabs would stay down. I went back to the lime supplier and they do not supply Adhere-cal, but did wonder how the floor tiles would pop off if laid in lime mortar.
So after much deliberation I am going to stick with the lime mortar, not with the adhere cal and take the risk with popping lime slabs.
So after much deliberation I am going to stick with the lime mortar, not with the adhere cal and take the risk with popping lime slabs.
Flyfisher
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Frustrating isn't it? Then remember that 'breathable' doesn't seem to have a generally accepted definition anyway and it's all a bit of a minefield. Plus, a diluted covering of 'latex polymer' (basically a thin layer of rubber?!) and 'polymer technology' doesn't sound particularly breathable.
However, bear in mind that you're already going to cover the floor with non-breathable slate (a material used in traditional damp proofing courses!) so perhaps it doesn't matter that much, especially if the glue was only applied to the underside of each tile and didn't cover the grout lines. But in practice the tiler will likely just cover the entire floor with the stuff unless you watch over him/her - which probably wouldn't make for a happy experience.
However, bear in mind that you're already going to cover the floor with non-breathable slate (a material used in traditional damp proofing courses!) so perhaps it doesn't matter that much, especially if the glue was only applied to the underside of each tile and didn't cover the grout lines. But in practice the tiler will likely just cover the entire floor with the stuff unless you watch over him/her - which probably wouldn't make for a happy experience.
CliffordPope
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Why not just lay them on sand?