Housing - Renovation: Bedding limestone pavers in wet Limecrete

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- CommentAuthortvrulesme
- CommentTimeFeb 9th 2022
Just finished excavating a floor ready for limecrete. I'm going to have 150mm compacted foamed glass, underfloor heating pipes followed by 75mm of limecrete. On top of this will be 20mm limestone pavers.

I came across this today where someone laid the pavers directly in to the limecrete.

https://limewindow.blog/2012/11/12/limecrete-floor-with-flagstones/

Seems like a great idea to me, saves on waiting for drying until floor surface goes down and also saves a little bit of head height loss.

Can anyone tell me any reason not to do it like this and wait for the slab to fully dry before laying the pavers?
- CommentAuthorDominic Cooney
- CommentTimeFeb 9th 2022
Ahh, this brings back memories...

If you look through their pics, you can see that they are working off an existing slab (assumed Limecrete)
but are using Limecrete again to set the slabs on. As expected really and same as how we did ours. If you think about it, "limecrete" is just a lime mortar with a different mix of aggregates.

We laid a 4 - 5" limecrete slab (100mm - 150mm in old money) then once it had gone off (enough to stand on) on top of the slab, UFH pipes cable-tied to A142 mesh to get an even spacing, then set the stone flags (in one room) and brick pavers (in the other) in a lime mortar mix made with recycled crushed glass (the consistency of sharp sand).

if you try and set your pavers into the mix for the slab itself, the slab will either be too wet to walk on and you will sink, or it will be too dry to set your pavers in securely and they will wobble or the floor level will be uneven.

To me, your layers don't seem thick enough - RFG, or slab, we did about 300-350mm of LECA as the insulating base layer and the slab had pumice in as the aggregate which also helps a bit with the insulation value. Are you sure a 3" slab will be up to it?
- CommentAuthorDominic Cooney
- CommentTimeFeb 9th 2022
Also just to add, your slab won't need to be "fully dry" before you do anything further like lay the pavers, because the floor is breathable, it just needs to be firm/strong enough for you to walk on (or wheel a barrow if required?)
- CommentAuthortvrulesme
- CommentTimeFeb 9th 2022
Posted By: Dominic CooneyAhh, this brings back memories...

If you look through their pics, you can see that they are working off an existing slab (assumed Limecrete)
but are using Limecrete again to set the slabs on. As expected really and same as how we did ours. If you think about it, "limecrete" is just a lime mortar with a different mix of aggregates.

We laid a 4 - 5" limecrete slab (100mm - 150mm in old money) then once it had gone off (enough to stand on) on top of the slab, UFH pipes cable-tied to A142 mesh to get an even spacing, then set the stone flags (in one room) and brick pavers (in the other) in a lime mortar mix made with recycled crushed glass (the consistency of sharp sand).

if you try and set your pavers into the mix for the slab itself, the slab will either be too wet to walk on and you will sink, or it will be too dry to set your pavers in securely and they will wobble or the floor level will be uneven.

To me, your layers don't seem thick enough - RFG, or slab, we did about 300-350mm of LECA as the insulating base layer and the slab had pumice in as the aggregate which also helps a bit with the insulation value. Are you sure a 3" slab will be up to it?

Thanks Dominic. So LECA is not load bearing whereas foamed glass is according to Mike Wye. They've checked the above specs and recommended 150mm for the foamed glass and 100mm for the slab itself so going for that instead. This also accounts for the solidness of the existing slab they would have.

Won't need to walk on this at all as it's for a holiday home that we can just leave to dry as long as it wants. We also conveniently have 3 entrances so they can work their way in one and out the others.

What I am trying to avoid is getting people in to lay the slab, go away and wait, lay the pavers, go away and wait, point the joints, go away and wait.

Slab and pavers in one go would be a lot less disruptive. I know this is a job you do once and once only but I think I could handle 1 day of watching like a hawk much more successfully than 2.
- CommentAuthorDominic Cooney
- CommentTimeFeb 9th 2022
Posted By: tvrulesmegetting people in

ah I see

if you use NHL5 for the slab it will be rigid for the next day. They can then lay out the UFH pipes and set the pavers in a limecrete or lime mortar mix, if this is also NHL 5 they can point it up the next day. in fact they could probably start pointing at one end before they finish laying the pavers at the other. (If they walk on it carefully)
- CommentAuthorDominic Cooney
- CommentTimeFeb 9th 2022
150mm doesn't seem like a lot of insulation for foamed glass but then I don't know the values of it. I know we needed a deep layer of LECA bit it's probably not as good an insulator as foamed glass.
- CommentAuthortvrulesme
- CommentTimeFeb 9th 2022
Posted By: Dominic Cooney150mm doesn't seem like a lot of insulation for foamed glass but then I don't know the values of it. I know we needed a deep layer of LECA bit it's probably not as good an insulator as foamed glass.

Thank you. Yes it's not that much, minimum really but it's not subject to builkding regs and better than the 0 insulation I had before
- CommentAuthorDominic Cooney
- CommentTimeFeb 9th 2022
We put 150mm of EPS under the current one, but its not a breathable floor construction,
so readymix concrete slab (150mm - ish) then UFH pipes cable-tied to A142 mesh at 100mm spacing, then set the brick pavers on top as we laid the screed (Sharp sand & cement mix).
I worked out the U-value for that as 0.188 which is better than the BRegs minimum of 0.25 for refurb but not as good as the 0.11 required for a new build floor (AIUI)
But in our case we couldn't dig out any further down because we got to footings. We could have used PIR insulation instead but would have cost more (twice as much if i recall) and I liked the breathable-downwards potential of the EPS.
- CommentAuthordjh
- CommentTimeFeb 9th 2022
I'm confused and concerned. You start by saying 75 mm of limecrete then later say 100 mm; which is it? Foamglas is stable because it has sharp edges, unlike leca which is spherical. So you most likely won't be able to lay UFH pipes directly on it. You'll either need some limecrete first, or some other blinding layer. Why is it not subject to building regs; where is it?

Walking on it is for the purposes of installing the pavers. As Dominic says, you'll need two stages of limecrete but they could follow one another fairly quickly.
- CommentAuthortvrulesme
- CommentTimeFeb 10th 2022 edited
Posted By: djhI'm confused and concerned. You start by saying 75 mm of limecrete then later say 100 mm; which is it? Foamglas is stable because it has sharp edges, unlike leca which is spherical. So you most likely won't be able to lay UFH pipes directly on it. You'll either need some limecrete first, or some other blinding layer. Why is it not subject to building regs; where is it?

Walking on it is for the purposes of installing the pavers. As Dominic says, you'll need two stages of limecrete but they could follow one another fairly quickly.

Apologies, I have queries with multiple companies open Mike Wye, Lincolnshire Lime etc so specs are changing as more info comes in. Using this excellent forum to help me test the ideas and come to the best proposal for my project

In terms of building regs I'm speaking mainly about insulation U values. It's a listed building and my planning department are more interested in retaining the traditional building aspects than meeting the regulations. Of course there are things that apply in terms of safety but the conservation officer has effectively waved the u values.

There are many ways to do Limecrete with Leca, glass foam and a whole variety of different ratios and depths so I'm just collating as much info to find the right path at the moment. The latest note from the technical team at Mike Wye is this advise

"150mm of the compacted GEOCELL would be fine, however if you are having underfloor heating then we would recommend having a screed of 100mm depth. This is to ensure that there is a sufficient amount of screed covering the underfloor heating pipes.

You would not be able to lay the limestone flags directly onto the wet screed, however you could apply the screed in two separate stages. You could put down 80mm of screed in the first instance, and then once this has been left to dry for 7-10 days, you could then go onto this with a further 20mm bedding for the limestone flags."
- CommentAuthorDominic Cooney
- CommentTimeFeb 10th 2022 edited
They seem to be talking about screed and slab as the same thing, so Iâ€™m guessing UFH pipes set into the thickness of the slab. The question is how are you going to do this practically?
It sounds like they are suggesting an 80mm slab, set out the UFH pipes, then 20mm screed to embed the pipes and set the pavers in, which is just about doable (with care if you DIY) but Iâ€™m not sure a builder would find that the easiest way.
The alternative is to set the UFH pipes within the first slab but they would have to be propped up a bit so that they are embedded (maybe on little stilts/props - I canâ€™t remember what theyâ€™re called) so this comes back to how are you securing the UFH pipes? So to do it this way you (they) have to walk all over the surface of the compacted RFG which again would probably be okay for DIY but how are the builders getting the limecrete across the room inside a listed building? (Wheelbarrows?)
I believe the compacted surface of the RFG is quite solid and then you would have a layer of geo textile (e.g. Terram) on top to keep the layers separate. We managed to walk and wheelbarrow over the LECA with terram but it was a bit of a waterbed!
If the UFH pipes are to be secured in eggboxes then you would also have a supportive layer of continuous plastic that they would be able to wheelbarrow across (although I do wonder if that defeats the principle of a breathable floor somewhat?)
I would like to see a cross-section drawing of the floor build up.
- CommentAuthorDominic Cooney
- CommentTimeFeb 10th 2022
(To see where the UFH pipes are)
- CommentAuthortvrulesme
- CommentTimeFeb 10th 2022
Posted By: Dominic CooneyI would like to see a cross-section drawing of the floor build up.

Yeah I have the same concerns. Here is the cross sectional area of their recommended system. Guessing that their proposal with the 80mm then 20mm would move the pipes up to the top layer of the screed. Not sure if this is worthwhile. Would be tempted to attach the UFH to the geogrid, do an 80mm layer, let it go off, follow up with the 20mm layer bedding in the stone pavers. Sound sensible?

In answer to my question as to whether you could lay 100mm and bed in the pavers they said

"It may be possible to lay the 100mm screed at once and bed the flags into it, however it is not what we would recommend, and it may cause difficulties from a practicality point of view."
- CommentAuthortvrulesme
- CommentTimeFeb 10th 2022
In terms of the practicalities of mixing and transporting I have 2 entrances where the mixer could be placed. It's the Kitchen and bedroom/Study I am laying with limecrete
- CommentAuthorDominic Cooney
- CommentTimeFeb 10th 2022 edited
The geogrid is the layer I didn't know about, that and the clip rails will lift the UFH pipes up into the slab (they are calling it the screed) that will keep the floor system breathable.
I don't know how the clip rails fix to the geogrid. Also the geotextile is in their drawing, which I was expecting.

I think you are there with it now, do it as their drawing but with 80mm of limecrete, and then set the pavers in the last 20mm - so as you describe.
- CommentAuthorjfb
- CommentTimeFeb 10th 2022
150mm of expanded glass foam equates to about a u-value of 0.3 I think.
Pretty bad - you are going to lose a lot of heat to the floor below.
Why not go a bit deeper?

I wouldn't attempt to lay the flagstones at the same time. Don't know how the work is being done but I imagine you would have enough to do trying to get the limecrete floor in and level before it goes off.
- CommentAuthortvrulesme
- CommentTimeFeb 10th 2022
Posted By: jfb150mm of expanded glass foam equates to about a u-value of 0.3 I think.
Pretty bad - you are going to lose a lot of heat to the floor below.
Why not go a bit deeper?

I wouldn't attempt to lay the flagstones at the same time. Don't know how the work is being done but I imagine you would have enough to do trying to get the limecrete floor in and level before it goes off.

Yes I'm being very careful with my foundations which are pretty sketchy. I'm going to try and get down to 200mm compacted to achieve the 0.24 in the chart below.

Yeah it was a nice idea about laying the flags at the same time but I think I've been put off with this discussion. That's what these forums are here for right?
- CommentAuthortvrulesme
- CommentTimeFeb 10th 2022
Posted By: Dominic CooneyThe geogrid is the layer I didn't know about, that and the clip rails will lift the UFH pipes up into the slab (they are calling it the screed) that will keep the floor system breathable.
I don't know how the clip rails fix to the geogrid. Also the geotextile is in their drawing, which I was expecting.

I think you are there with it now, do it as their drawing but with 80mm of limecrete, and then set the pavers in the last 20mm - so as you describe.

Top man, thanks a lot for all the help
- CommentAuthortvrulesme
- CommentTimeJul 2nd 2022
Finally got my Limecrete floor down so I thought I would share some pics :)
- CommentAuthortvrulesme
- CommentTimeJul 2nd 2022
Screeding
- CommentAuthortvrulesme
- CommentTimeJul 2nd 2022
He looked like he was enjoying compacting the geocell but he said it was a pain
- CommentAuthortvrulesme
- CommentTimeJul 2nd 2022
I'm going to be laying limestone tiles on top. As it's a kitchen wondered if I should seal with a breathable sealant and if anyone can recommend a good one?

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