Laying a Limecrete Floor

[MatthewC]

I am taking the plunge of laying a limecrete floor in my kitchen. I've researched the topic on this forum (and elsewhere) and need some advice please, hopefully from someone who has actually done this.

The design I have been given uses a base of coated LECA, 200mm thick (with a membrane above and below) with a 100mm slab of NHL5 and uncoated LECA next, and a 75mm screed of NHL5 and sharp sand on top of that. We then intend to lay black limestone flags on a mortar bed which will add a further 50mm to this, making a total thickness of 425mm. I intend to excavate on a 45 deg slant away from the wall which has foundations extending about 9 or 10 inches below the floor level.

My questions:

1. This thickness (= 17 inches) seems to me to be quite a lot! Is there any scope for reducing this?
2. When I dig down on the 45 deg slant, how far down below the floor level should the 45 degrees start?
3. When laying the LECA and slab, does the LECA move as the slab is laid? i.e. does one lay the entire LECA first and then the slab, or can you work gradually along the room laying LECA a couple of yards ahead of the slab mix?
4. When mixing the NHL5, are there any techniques/tips I should know?
5. As it is a listed building (and I do have LBC), am I right to say that Building Control cannot insist on any specific depth or design of floor?

I'd appreciate any advice on the above questions and anything else that would help!

Matthew
http://houseintheenchantedforest.blogspot.com/

 

[MdB]

I don't think there are too many people here who have done this. The amount I've done (about 1sq m total) doesn't really count but I'll comment anyway ;-)

1) Your thickness sounds about right compared to what I remember looking at.

2) You really need an expert on this to comment. Structural stuff depends on lots of things and if you get it wrong you need a new house... There have been pictures posted here regarding a house that collapsed due to the floor being dug out too far.

3) I would lay it all at start. It is fairly round - especially the coated stuff so will shift.

4) For the volume you will need, I believe a roller pan mixer is what you want rather than a drum mixer. Not used one myself though - others are more expert.

5) I think that depends on the power struggle between the CO and BCO... Be careful not to get stuck between the middle of the two.

Also think about drying times. My little patch of limecrete laid 4 weeks ago in a house heated to 20 degrees with the windows open whenever appropriate is still too damp to walk on without leaving footprints. It was probably a bit too wet when laid but even so I would have expected it to have dried out by now. NHL will set wet so this may be less of an issue for you.

 

[robgil]

425mm seems excessive to me also. Its simply to enable the floor to meet the demands of insulating. I have always wondered if simply laying a modern insulating material such as cellotex and leaving gaps in the cellotex to allow breath ability and also a gap around the edges (apparently 300mm is acceptable) to keep the walls dry would be a better idea than digging down so deep?
I am no mathematician but 400 odd mm deep at a 45 degree angle would put the insulating a fair bit back from the wall anyway.

Also I believe the floors of old houses , especially houses that originally had no flooring at all, are of just as much if not more archaeological significance than the house itself.

 

[oxalto]

Matthew - I am looking to do a similar thing and posted about it a while ago but there was little response. I don't think that many PPUK users have used it. I'd be very interested to see how you get on, though. Would you mind me coming to have a look when you're doing it as I'm nearby?

 

[MatthewC]

I am no mathematician but 400 odd mm deep at a 45 degree angle would put the insulating a fair bit back from the wall anyway.

400mm to be exact!

 

[MatthewC]

Well, today we have laid the slab on the loosefill LECA. I must say that when I decided to replace the floor (and it was indeed very damp under the old floor, which was only 4 ins total depth), I didn't realise that I would be one of the first on this forum to explore this technique. We had the Building Control Officer come round today, and he had never seen one before either - I hope he was enlightened and possibly even impressed by my explanation.

I don't think now that the depths were excessive; in fact I rather wish we had trimmed the earth closer to the walls. We used 81 out of 84 bags of the loosefill coated LECA, and 38 out of 42 bags of the uncoated which was mixed with the NHL5. Now for the screed!

Matthew - I am looking to do a similar thing and posted about it a while ago but there was little response. I don't think that many PPUK users have used it. I'd be very interested to see how you get on, though. Would you mind me coming to have a look when you're doing it as I'm nearby?

I'm very pleased to show the results to anyone, and give you full details of our technique. I can even recommend someone to help you - the two lads who helped me (who had done floors before, but not limecrete) have been brilliant this week and have worked like Trojans.

I'll be putting a more detailed entry about it on my blog tomorrow or Saturday.

Matthew
http://houseintheenchantedforest.blogspot.com/

 

[MatthewC]

Well, as I have reported on my blog, we have now laid the screed on the slab, so the limecrete floor in the kitchen is virtually complete. See photos on the blog http://houseintheenchantedforest.blogspot.com/. It is going off nicely - NHL5 certainly appears to set fairly fast, although if you brushed the surface after a few days it was clear that actually it was still workable. Today (after six days) I dared to allow the plumber to work on/above it, and it survived!

One thing with which we had trouble was that the slab sank a bit, because of the loose lay LECA. This caused the three inch screed to be nearer four inches in depth in places in order to bring it to the right level, and so we needed more material than expected. I was aware there is a danger of crushing the loose LECA (which would introduce particles and so would negate its purpose), and so we were rather afraid of doing that. Apparently (no one told us before), you do need to tamp it fairly well, or else the slab sags as we found out. Live and learn!

I'm now (still) awaiting approval from the council for our limestone flags - they are soooo slow. I cannot see why they want to go into some detail so deeply (like the exact type of woodburning stove) when they don't go after people nearby who have ignored planning/conservation/Building Control entirely!

Matthew
http://houseintheenchantedforest.blogspot.com/