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 FoamGlass 40, 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 FoamGlass 40 are on our shop along with a very handy calculator which instantly works out quantities required of foamed glass, 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 Foamglass40 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 75-100mm. The lime screed is applied as a semi dry mix using a good quality eminently hydraulic lime, such as Socli’s NHL 5 lime, mixed 1:2.5 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.

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.

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).

Installation Instructions

1: Base Substrate Preparation.
When the existing floor has been removed, excavate ground to required depth. It is important to level and compact the surface as variations in levels can increase material consumption. A laser level may be used to ensure ground is level.

2: Geotextile Membrane
Once level and clean lay the Geotextile membrane on the substrate. Make sure the joints of the membrane overlap. Leave enough membrane on the edges to be able to fold onto the top of the Foamed glass.

3. Foamed Glass
The max depth of Foamed glass to be installed at a time is 300mm. If more depth is required it should be laid in layers. The advantage of Foamed Glass 40 over other products on the UK market is it’s compressive strength meaning compaction is only 5-10% where other products can be up to 30%. Also the minimum recommended depth of Foamed Glass 40 after compaction is 100mm where as other foamed glass products it is 120mm.

4. Distribution
Use a rake or shovel to spread the Foamed Glass evenly across the whole area.

5. Compaction
Using a vibrating whacker plate to compact the Foamed glass base down to your finish level. Find a method that works for yourself but using the whacker plate onto scaffolding board laid on the foamed glass helps to achieve consistent compaction. Once the foamed glass is compacted and level fold over the rest of the bottom layer of membrane then lay your next geotextile membrane on top, taking care to overlap joints.

6. Underfloor Heating
Limecrete floors are fully compatible with under floor heating. If installing underfloor heating, now is the time to fit your underfloor heating system on top of membrane taking care not to puncture the membrane. Then cover with 75mm layer of limecrete.

7. Perimeter Board
Fit the cork perimeter board around the edge of your floor area making sure that the cork
board finishes at your final floor level height.

8. Limecrete
Mix limecrete at 2.5 parts screeding aggregate to 1 part NHL 5 by volume, adding sufficient water to make a stiff / semi dry mix, which holds together when squeezed. Reinforcement fibres are recommended. (1 kg per tonne of aggregate) to provide tensile strength. Ideally mix for 20 minutes after adding sufficient water. When laying the limecrete finish, tamp with a wooden or steel tamper. Float with a timber or polyurethane float. The final surface should be screeded and tamped in a float screeding manor, then scoured with the float and trowelled.

10. Aftercare
Limecrete should always be kept damp for a minimum of 96 hours and protected from freezing conditions for the first 10 days after laying. Traffic should be avoided during this time and there after protective boards should cover the work for 3 weeks. If you have installed underfloor heating this should not be used for a minimum of 4 weeks.

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

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