Laying a Limecrete Floor Part 2

This week has seen the completion of a major item on the critical path for us to move in: the slab for the limecrete floor has started to go off very quickly - as I was told that NHL5 would - so we have laid the screed.  Again I had Chris and Shane to help - Chris had done a few floors before (but not in lime), and Shane was expert at mixing (but not lime), so they relied on me for the technical input.  I relied on Mike Wye and the internet!

The screed uses NHL5 and sharp sand, in a 1:2 mix by volume, 75mm thick (as advised by Mike Wye). Be advised that a LOT of sand is needed!  For some reason I have had trouble in calculating the required amounts of sand and NHL5, and we ran out of both during the first day, so stopped with two-thirds completed (see join across the floor in the photo on the right).  I bought some more of everything and we finished the job two days later.  It was much easier to do than the slab, as we had a decent solid base to work on, and Chris now loves to work with lime.

Chris is a bit of a perfectionist and was slightly upset with the need for a join; he was then even more upset to discover that the last half tonne of sand was from a different supplier and so was a darker colour (although you can't see it in the photo).

This is me not Chris as I deleted the photo of him by accident

He was not comforted by my reminder that we are laying flagstones on top and so neither the colour change or the join will be seen.


The sand situation was not helped by my general lack of understanding about volumes and weights of sand.  I suppose I should not have been surprised as, after all, I knew how much stuff had come out of the ground in the kitchen.  We ended up using just over three tonnes for a 21 sq metre floor.  As I expected to use less than two tonnes, I had a one tonne bulk bag of sand delivered, and supplemented this with repeated visits to a local DIY store to buy their loss-leading bagged sand at £1.07 for a 25kg bag (in a quantity of ten or more).  The result of using more than three tonnes was that I made a lot of unexpected visits, and they ran out!

So far as I can tell, our floor must be thicker than designed - perhaps the slab sank a bit on the loose lay LECA?  We laid the screed up to a fixed level (as opposed to laying a specific depth), so it might have been deeper in places without us noticing.  Otherwise I do not see where all the mix went went.  The floor area is 21 sq metres and I was told I would need 21 bags of NHL5 (i.e. one per sq metre); we had four bags left from the slab (why?) so that made 25 to start with, and yet we ended up needing 30 altogether - so each mix only did 0.7 sq metre.

For the technically minded, we used a large diesel drum mixer on hire as we realized that my own mixer was too small - we would have been doing twice as many mixes!  In truth, the hired mixer was also too small, as it took 30 mixes to do the screed; if you overload it then it won't mix properly.  Each mix comprised one 25 kg bag of NHL5 (30-35 litres) and four and a half 25 kg bags of sharp sand (about 70 litres), and used about 15 litres of water.  Other people recommend a pan mixer for better mixing - we did not experience much balling, having followed the mixing method recommended by the manufacturers (although there was more balling with the LECA - see Part 1 - and we did have to stop it and scrape the mixture off the interior, which was tedious).    One unexpected issue was that my wheelbarrow is now on its last legs - two welds have broken and the sides have bowed out.

Then it was the weekend so I went to see my grandson:

Proud Grandad with sleeping grandson

This blog entry was late in being uploaded for various reasons such as tiredness.