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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentTimeJul 23rd 2007

    I am planning to lay a limecrete floor in a couple of weeks or so and would like some advice?

    I have a floor area of 25sq m in a C14th timber framed house, with minimal foundations. I would like to remove the concrete floor and lower the overall finished floor level by about 100mm. The floor level is currently higher than it was when it was bricked.

    I would also like to include an underfloor heating system in the top screed.

    Would it be possible to lay a 'border' of LECA or ballast based limecrete, butting up to the foundations, of say 500mm wide. Then lay the membrane / LECA / membrane / limecrete-LECA / screed (with UFH)?

    Lots of questions.

    Any educated answers?

    Many thanks

    Newbie Gary
    Foundations? That's a rare thing in a building of that age! I work on 18th and 19th century houses, and they don't have foundations. What you'll probably have are large boulders and rocks bonded with rammed earth on which the walls were started. The standard procedure for limecrete floors in such situations is to ensure thay you leave a 45-degree batter on your excavation to ensure that the walls' substructure (foundations, if you like) isn't compromised in any way. Under no circumstances dig straight down in an attempt to create a 'neat' straight-sided hole, or you'll end up having to underpin.
    The geotex is laid to continue up the slope to just above the top of the finished slab and then the leca (or, better still, foamed glass) is spread and compacted right to the edge before the second geotex mesh goes on top.Obviously the leca/glass will be thin near the walls, but the slab can then be laid at a uniform thickness, UFH pipes fixed and screeded as per normal.
    There should be no need for any border or reinforcement.
    If the final floor is to be below outside ground level you will probably wish to consider the external drainage to prevent moisture penetration. Also, lowering the floor in such a building may require LBC.
    • CommentTimeAug 15th 2007
    Well I've done it now.

    Not actually below the foundations, but to the bottom of them on the inside. Due to the unstable nature of the loose fill LECA I was not prepared to trust it to support the sides of the flint/brick on the inside. So I have created a 'ring beam' with NHL5 and ballast. This was poured in trench created in the clay base. When that had set I filled the rest with the standard loose fill LECA/ LECA NLH5 mix (3:1). (120 batch mixes!) I did as Gervase suggested cutting back at an angle from the outside as to to remove too much packed earth/fints etc.

    UFH pipes were layed in in the plastic clip strips which were attached by drilling staight into the LECA/lime. Just finished the 50mm screed, so need to wait 28 days for it to set! I kept the UFH pipes to the LECA area otherwise the heat would be conducted outside! The room is backed up with a large fireplace, so I hope it will now be warm enough.

    I have learnt that NHL5 mixed will begin to set within a couple of hours, so if you are on your own (like me) then you need to work fast. I used CASTLE hydraulic lime, which in my opinion seems slightly inferior to St Aister. Plus it's grey rather than white, so if you are using it as a grout for clay tiles then I would use the St. Aister product as it's white.

    It sure is an eco breathable solution, and no doubt wiil benefit the building's structure. I'll keep this forum posted on any updates.

    Can anybody advise on the NHL/sand mix for grouting/setting tiles on?
    Fantastic thread! I too am considering using LECA and limecrete for a 25 sq meter floor. Gary, please may I ask roughly how much Natural Hyrdaulic Lime you used? When you say you did 120 batch mixes, does that mean you used 120 x 25kg bags?!?
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