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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorPigglet
    • CommentTimeJan 2nd 2017
    I'm currently in the process of doing this in a 300 odd year old cottage to create a breathable floor.
    The plan is to lay a 80mm UFH limecrete slab over Geocell insulating aggregate and finish with a sandstone floor pointed with lime grout.

    Basic floor slab spec is non woven membrane, geocel, nonwoven membrane, geogrid (will expand on this) UFH pipes, Limecrete slab.
    I've got so far as getting the geocel down and wackered however this has been rather tricky as the lumps of geocel are quite large and being light they move around easily. I took my time to ensure the fill was spot on level using a rotary laser and long levels (note, this took a lot longer than with dolomite or similar).

    As soon as I tried to wack it down the wacker started pushing it around. I tried 3 different wackers, ranging from a little amman wacker to a large forward and reverse wacker I use on road work. The smallest and lightest worked best. (large wacker wasn't really practical in such a small cottage but wanted to see if it would help with compaction)

    The supplier stated that the geocel should compact by 25%, it has not compacted by anywhere near this amount, probably around 12% in reality hence my trying the large wacker. I didn't want to keep running the wacker over it as after a few passes it didn't seem to compress any further and I was worried about shaking a 300 year old terrace to pieces!

    Having got this far the next issue I can forsee is that the geogrid provided by the supplier for the purpose of attaching the underfloor heating pipes to is nothing more than thin flexible plastic fencing mesh.
    As the geocel is effectively a loose fill even after wacking there is no way of anchoring this mesh down and as such I am sure that when I try to lay and cable tie the UFH pipe to it, will just lift and distort due to the UFH pipes tendency to want to spring straight. I think I'm going to have to shell out for some steel reinforcing grid to clip the pipes too.

    Has anyone else done this and is so what were your conclusions? Any tips or tricks? Based on experience So far I'm less inclined to go down this route again in a small building due to the difficulty of getting a level Geocell base for the slab.
    • CommentTimeJan 2nd 2017
    Here's a couple of links for anyone not familiar with the product:

    I used a similar product (technopor) in some parts of my build and I too found I couldn't get it to lock into a level surface - fortunately it didn't matter in my case.

    I see that in the limecrete photos in the link I posted, they use sheets of something - thin ply? - to give a surface they can walk on during installation.

    It sounds like you will need some weight to anchor the geogrid in place. Steel mesh should definitely do the job, but perhaps you could succeed by tying bricks or even lumps of concrete to the grid at points where it tries to lift up. In fact perhaps just putting something heavy on top of the grid at places where it lifts would be enough?
    • CommentAuthorgyrogear
    • CommentTimeJan 2nd 2017
    Posted By: PiggletHas anyone else done this and is so what were your conclusions?

    Basically, "No", is the short answer. I am laying my limecrete slab over a compacted sub-base of dry mud because the tubes are not for UFH, but for injecting heat to ground, so different other method...

    I tied off to a mesh made of bamboo canes, spragged across the four sides of the slab (I only do 2 x 2 meters at a time, as I am hand-mixing...). I found that this mesh had a tendency to "float", so I nailed it down in a few places with paired wooden pegs, with nylon-twine frappings. That worked OK.

    I actually ballast over the tubes with 2 inch of bought-in (clean) gravel, then pour a liquid screed.

    This is probably not much use in your set-up, but feel free to whisper me and I'll send U some photos.

    Good luck,

    • CommentAuthorSilky
    • CommentTimeJan 2nd 2017 edited
    just wondering what depth and size of foamglass you used and whether you had to compact it in layers? I would also like to avoid similar problems when I do something similar
    Limecrete/Foamed glass floor demonstration video


    Tamper as recommended by the limecrete company for corners/high spots or bits that pop up while turning with the compactor.


    Cable tie underfloor heating pipes to reinforcing wire or mortar dabs while laying the screed.

    Watching someone with experience lay the floor makes it look very simple.
    my experience is you dont get the 25% reduction and the gear moves around a lot , a ply sheet over the top as suggested is good.
    it wont work like type 1 mod or similar hoggings
    lay the fabric and whack again, a tamp is useful , try and flatted the roll under pressure prior to work , perhaps cut to length and press between 2 ply sheets with weight on.
    • CommentAuthorPigglet
    • CommentTimeJan 3rd 2017
    Thanks for the replies people. Look like I'm going to have to rake some geocell out to get the correct slab thickness.
    Yes, the video above makes it look very simple but in a small cottage with alcoves and walls projecting into the room its considerably trickier!

    Even trying to lay the membrane over the top of the aggregate drags it out and upsets the level considerably.

    I'm not sure exactly what size the Geocell I got is classed as, It has gone down in one layer and as 225 mm fill depth supposedly compacting to 170mm but its not compacted to anywhere near that.
    • CommentAuthorYanntoe
    • CommentTimeJan 4th 2017
    Hi Pigglet,
    I've recently done this and don't worry, you are not alone. It really is a difficult and worrying undertaking.

    I persevered with a heavier thwacking plate which also had went into reverse. This was very difficult and frustrating as, like you I have many corners and alcoves. As the plate tends to dig in l found that it was best to avoid the corners as far as possible and then get a heavy lump hammer and a 4 foot plank, lay the plank along the edges of corners etc and hammer it down. Split plenty of planks, but it seems to work.
    I found it very difficult to get the plastic mesh flat, but in some ways the pipework helps. I put bricks on the areas where the pipes/ mesh lifted and then used dollops of limecrete to hold the stuff down as we layed the limecrete. We also put in screeds on limecrete ridges to get things level and this also helps hold things in place until the limecrete covers the pipework.

    Once the limecrete is down the horrors of the process recede and it all seems ok.

    Interestingly, one of the limecrete floors adjoins a modern concrete slab with 150mm celotex slab of insulation. It's in the same airspace and should therefore be at the same temperature. Several of us have noticed that there is a noticeable difference in the temperature of the floors if walked on without your shoes on. The limecrete feels warm and the concrete feels cold. Neither has its final floor covering on and neither is currently heated.

    In our kitchen (around 40 sq meters) we have a limecrete floor with ufh under slate. Our cooker is a woodburning ESSE ( think AGA but made in Barnoldswick). The room sits a 20degrees C 24/7 and the floor feels warm. We let the ESSE go out 2 days ago and turned in the UFH. The room stays at 20 degrees, the floor feels exactly the same but the air is less "comfortable".

    With all these floors the depth of foamed glass is different, partly by design but mostly because the difficultty of getting it level. The pipework, may not be exactly at the depth it should be but it all seems to work OK and seems to take more punishment than expected with no ill effects. So, persevere and don't worry do the best you can, It'll be fine! The rants and depression with installation will all be forgotten once the floors down and the heats stays in whilst the moisture stays out.
    (Our RH has fallen from over 80% last winter to 50% this winter)

    Good luck
    • CommentAuthorPigglet
    • CommentTimeJan 5th 2017
    Thanks for the response yanntoe. That's reassuring to hear! Ufh is now down going to lay the slab next week. If I have to do this again I will definitely avoid the plastic Geogrid and lay proper stainless reinforcing mesh to clip the pipes to. The Geogrid is awful to use and if the extra time required to lay out the plastic grid and then faffing about with weighting it down etc is taken into account then the extra cost of the stainless mesh is more than off set by the time saving.
    • CommentAuthordelprado
    • CommentTimeNov 9th 2017
    Hi Piglet

    How has the project gone? I am about to do something very similar to you!

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