How do I lay a breathable slate floor?
Can you tell me how to lay a breathable slate floor? I have read on the Period Living website that a previously suspended floor can be built up with limecrete. I am, however, unsure as to what tile adhesive, grout or sealant to use.
Rachel Ganner, by email
Michael Holmes replies: Providing the slate you choose is not too heavy or thick it may be possible to lay it over the existing suspended timber floor. You’d need to lift the existing floor, strengthen the joists, add insulation between them (either rigid board on battens, or mineral wool suspended on chicken wire) and finish with flooring grade chipboard. You can then lay a de-coupling mat such as Ditra Mat or Durabase followed by your slate tiles, lay with a flexible tile adhesive and grout. Finish the slate with a breathable sealer such as Lithofin Stain-Stop.
If you take this option it is very important to make sure the void beneath the floor remains well ventilated. You could also add underfloor heating, either using warm water pipes suspended under the chipboard, or electric elements laid over the chipboard.
The only problem with this will be the increase in finished floor level, which may or may not be acceptable, depending on the thickness of your slate. If you want to retain the same existing floor level, then laying a new limecrete slab will support your slate floor and keep the building dry.
Limecrete is a flexible and breathable alternative to concrete, made using hydraulic lime and well graded aggregates. Limecrete can be laid on to a breathable geotextile membrane, either over compacted ground, or compacted hardcore and sand blinding.
Mike Wye & Associates (mikewye.co.uk) has developed an insulated limecrete floor that will meet the building regulations requirements for energy efficiency. It uses light expanded clay aggregate (LECA) beads as a loosefill material beneath the limecrete, and within the limecrete slab. The slate can be laid over the limecrete using a lime mortar and grout. Leave plenty of depth for the thickest parts of the slate, working backwards from your desired finished floor level.
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