How to Make a Limecrete Floor (One Way)

​So you need a hard slab on your floor but you don’t want to use Portland cement, because you’ve done your homework (or learned from experience) and know that Portland cement floor slabs are bad news in natural/ancient buildings. In this case, what you need instead is limecrete.
 
It still baffles me how few mainstream builders use lime, especially limecrete. I really don’t get, it to be honest. Are they scared? Too stuck in their ways? What is it? Lime isn’t any harder to use than Portland cement. It takes longer to cure, which means it’s a lot easier to correct mistakes than if you use Portland. It looks a lot nicer, too. It’s cheap, uses a quarter of the fossil fuels to manufacture, and it will pull damp out of buildings like nothing else. If you’re in a wet climate, lime is the way. What’s not to like?
 
Luckily for us, a friend of mine who shall thus be called ‘S’ has shared how she and ‘E’ made their limecrete floor for their Victorian cottage in Lincolnshire. Yes it’s to code, too.
 
How S and E Made their Limecrete Floor
 
Because S and E are in the UK, there are building regulations that have to be observed. But the system outlined here was pre-approved so it’s a great guide for anyone looking to make a limecrete floor system. Here we go:

Geotextile membrane shown by the lilac arrow.

​1. First, because this is an old house that someone had unwisely stuck a concrete slab in (damp issues in abundance), the existing concrete floor had to be dug out to a depth of 30cm. You can do this yourself but it’s a nasty, heavy job requiring serious machinery, so you may prefer to get a builder in. “We removed all the rubble ourselves, seemed about a million wheelbarrowsful. You have to remove absolutely every bit of it, because if you don't any sharp bits leftover will puncture the geotextile membrane,” explains S.
 
2. The geotextile membrane (shown above with the lilac arrow) stops the dirt travelling up into the glapor insulation. Once you have a rubble-free base to your floor, you lay the membrane.
 
3. Next, S and E added the Glapor insulation. Glapor is foamed recycled glass and laid to a depth of 30 cm throughout. “More long days of shovelling and wheelbarrowing,” laments S. 

Glapor is foamed glass and used for insulating floors.

4. The next stage was to compress the glapor to 20cm. For this, you need a plate compactor. "There's just no other way to do it," S says, "It's a nasty, noisy, heavy, slow job.” (He he he, I think a picture is emerging here).
 
5. Not yet defeated, once the glapor was compacted S and E then put down another layer of geotextile on the top. This stops the limecrete from sinking down into the glapor.

Geotextile on the top of the glapor to create a barrier for the limecrete, with geo-grid for heating on top.

​5. Because they were laying underfloor heating, S and E installed a geo-grid to hold the pipes in place, before laying the pipes themselves. They then used a pressure pump to pump water through the pipes to check there were no leaks, because once the limecrete goes down, that’s it! You can no longer access the pipes.

Water pipes going down for underfloor heating.

​6. Once that's all done, the limecreting begins. First, you shutter off the section you're going to limecrete. “Obviously, start furthest from the door and leave the area around the door to last. Limecrete is much more forgiving than concrete and can be done section by section, provided you do the sections quickly enough that it doesn't dry out,” explains S.

You can see the limecrete poured in sections here between the shutters.

​7. The limecrete mixture was made as follows: “Our builder lent us a concrete mixer. The mix we used was 2.5 buckets of slabbing aggregate and one bucket of NHL lime, with a handful of fibres added for strength. Because of the slabbing aggregate we used, we did not need to use sharp sand, but many other systems do require sharp sand. You then add water bit by bit until the mix is the consistency of stiff porridge. Keep it mixing for 20 minutes, then empty into a strong wheelbarrow and wheel it indoors.”
 
8. While one person lays and tamps the limecrete in the shuttering, the other person mixes the next load. Once the entire section is laid and tamped to the level of the shuttering, you can finish it with a float or trowel, and create the type of surface you want.

9. Finally leave the limecrete overnight, before removing the shuttering on that section and setting up an adjacent section. Continue until the whole floor is limecreted.
 
10.  Limecrete takes about three months to fully cure, but you can walk on it long before that. If you’re in a hot, dry climate, you need to damp (but not soak) the floor regularly to prevent it from drying too quickly and cracking. Once it's cured, use a stiff brush to remove all the loose dust. “You will need to do this repeatedly for quite a long time,” says S.
 
Something tells me S is happy this floor business is over:)

​Last word on the matter from S
"This was by far the biggest, heaviest, hardest, nastiest job we had to do, but once we'd done it, we felt like we could tackle anything because no job we're likely to do here now will be as physically taxing as doing that floor!"

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