Insulated Limecrete Floors

What is a Limecrete Floor

Breathable, insulated and limecrete floors have become quite common in the UK and hopefully you’ll find that this guide helps you understand how to apply a limecrete floor in your old building. The need for ground floors in older buildings to be breathable is essential. Why is this the case for older buildings? In modern construction the damp proof membranes run under the walls as well as the floor.  When impermeable membranes have been used in the refurbishment of old buildings these membranes finish at the walls resulting in concentrations of dampness in these areas and rising damp where it had not previously existed.

It has long been recognised that for old buildings it’s important to avoid pushing dampness from the ground into walls, which results in rising damp problems.  This has often been caused by the practice of retrospectively installing none draining compact fill, a cement base and impermeable membranes.  This practice is often made worse when gypsum plaster or tanking has been applied to walls, trapping the moisture within the masonry.


The Process

By using a well-insulated and free draining subbase of Foamit 30, wrapped in a Geotextile breathable membrane, and finished with a limecrete slab you will prevent dampness rising up the walls. Why do these floors provide good insulation? It’s the air trapped within the foam glass that provides high thermal insulation.  The lime screed mix is also designed to retain heat, acting as a thermal store.  It will also transit heat from any water based under floor heating system to the surface.

Full details of Foamit 30 are on our shop along with a very handy calculator which instantly works out quantities required of Foamit 30, geotextile membrane and materials for the limecrete slab – as well as providing the U value you will achieve, a U value of 0.25-0.3 is often recognised as ideal.

Before laying a breathable insulated floor it is essential to check the water table would not get higher than half the depth of the subbase, and that the site immediately around the building is well drained. In addition the foundations of the walls should never be compromised by removing ground from below the level of the existing foundations

The Build Up

The build-up is fairly straight forward no matter the size of the area and I’ve attached a few case studies for your review.  Ideally you want to be looking at 125-250mm of free draining ‘Foamit 30’ for the subbase laid on and wrapped in a Geotextile membrane.  If you’re considering underfloor heating then apply at this stage on top of 75mm polyurethane insulation. 

 A lime screed slab is then applied at 65-100mm.  The lime screed is applied as a semi dry mix using a good quality eminently hydraulic lime, such as Socli’s Ionic NHL 5 lime, mixed 1:3 with a screeding sand such as Waddington Grit sand.  We also recommend the addition of glass fibres at 1kg per 1 ton of sand, to provide additional reinforcement.  It is also advisable to use 30mm cork boards up against external walls before applying the lime screed.

Larger Floor Areas

For larger floor areas with heavier loads such as churches and community facilities, the installation of a limecrete floor requires a greater depth of build-up to cope with heavy and more variable loads. This is achieved with the installation of a 100 mm limecrete sub slab, before the screed is applied. The limecrete sub slab is made from one part NHL 5 lime and three parts of well graded lightweight fired clay balls 0-20 mm (as used Wakefield Cathedral) or 1 part NHL5 and 3 parts sharp aggregate and ¼ part 10mm limestone chippings (as used at Lambeth Palace).

No special skills are required for installing the limecrete flooring system, it is not unlike laying a conventional cement-based floor. The finished floor covering can then be applied with confidence that the subbase and lime screed are providing free drainage.  The finished floor could be stone flags or tiles pointed with lime mortar, or wood on battens.

We really hope this information assists to explain what a limecrete floor is and the build up needed to install one, if you need any further assistance give the experienced team in the office a ring