Limecrete floors: a breathable slab for buildings that need to breathe.

What is a limecrete floor?

Limecrete is a floor slab made with a lime binder instead of cement, usually laid over a bed of recycled foamed-glass aggregate that acts as both insulation and a capillary break. The result is a solid, insulated ground floor that remains vapour-open: moisture in the ground beneath can evaporate slowly and harmlessly through the floor build-up, rather than being sealed in and pushed sideways.

That makes limecrete the natural partner to lime-plastered walls and lime-pointed masonry. Old buildings work as a whole system — walls, floors and roof all managing moisture together — and a breathable floor keeps that system intact where a sealed concrete slab breaks it.

Why concrete floors cause damp in old houses

Most old houses originally had flagstones, quarry tiles or suspended timber laid over the earth, all of which let ground moisture evaporate gently into the room. From the mid-twentieth century onwards, many of those floors were dug out and replaced with concrete slabs over plastic damp-proof membranes. The slab itself stays dry — but the moisture in the ground does not disappear. Blocked from rising through the floor, it migrates to the nearest escape route: the base of the solid walls.

• —Damp concentrates at the wall bases, showing as staining, blown plaster and salt bands at skirting level
• —The problem is often then misdiagnosed as rising damp and treated with injected chemicals and cement tanking, which trap the moisture further
• —Timber in contact with the damp wall base — skirtings, joist ends, stud partitions — becomes vulnerable to rot
• —A vapour-open limecrete floor removes the blockage instead of fighting the symptoms

How a limecrete floor is built up

A typical insulated limecrete floor is a straightforward sequence of layers, though the exact specification is designed for each building and ground condition.

• —Careful excavation of the existing floor to the required depth, working by hand near wall bases and avoiding undermining shallow footings
• —A geotextile layer over the compacted formation to keep the layers separate
• —A deep bed of recycled foamed-glass aggregate, compacted in layers — this provides the insulation and acts as a capillary break, without a plastic membrane
• —The limecrete slab itself, a lime-and-aggregate mix laid to a level finish
• —Underfloor heating pipework where wanted, fixed above or within the screed zone
• —A breathable lime screed to receive the final floor finish

Lime cures more slowly than cement, and the programme has to respect that: each stage is given proper time before the next, and the slab is protected from frost and rapid drying while it gains strength. Rushing a limecrete floor is the most common way to spoil one, so we build the curing time into the schedule from the start.

Underfloor heating and floor finishes

Limecrete and underfloor heating are a natural pairing, and most of the floors we install include it. The insulating foamed-glass layer directs the heat upwards into the room, and the gentle, low-temperature warmth of underfloor heating suits both lime and the old buildings it goes into — no radiators on lime-plastered walls, and an even background heat that helps the whole building stay dry.

The finish on top must stay breathable for the floor to work. Suitable finishes include natural flagstones or quarry tiles bedded and jointed in lime, unglazed clay and stone tiles in a vapour-open adhesive and grout, or a polished breathable lime screed left as the finished surface. Vinyl, epoxy coatings and impermeable sheet materials would seal the floor and defeat the point; where a client wants timber, we detail it so the floor beneath can still breathe.

Our limecrete floor service

• —Full insulated limecrete floor slabs over recycled foamed-glass aggregate
• —Breakout and removal of failed or damp-trapping concrete floors
• —Floor build-up design to suit the building, ground conditions and finished levels
• —Underfloor heating integration within breathable lime screeds
• —Flagstone, quarry tile and stone floor finishes bedded in lime
• —Limecrete for extensions and new work where a breathable, lower-carbon slab is wanted

Where we work

We are based near Newport and install limecrete floors across South Wales and the West Country — including Cardiff, Monmouthshire, Abergavenny, Hereford, Gloucester, Bristol and Swansea. For the right building we will travel further; get in touch and tell us about the project.