Limecrete FAQ

Frequently asked questions about limecrete

What is limecrete?
Limecrete is a combination of natural hydraulic lime and lightweight aggregate or sand which can be used as an alternative to concrete. This creates a breathable floor slab with a certain amount of flex.

We never include any cement or admixtures in our limecrete. This would negate the breathability. We do add fibres to furthermore strengthen the floor.

What are the benefits to the building of using limecrete?
Limecrete is breathable. It behaves in a similar way to other natural building materials such as timber, straw and earth. Water vapour can escape through limecrete. If you have a waterproof floor and breathable walls water vapour would tend to travel up the walls, damaging them.

Limecrete is widely specified by architects to protect ancient buildings. We are fully insured to carry out work on listed properties.

How long does limecrete take to set?
This depends on various factors such as the lime type and content, whether it contains fibres and the ambient temperature. It is possible to move over the floor using boards after a few days, no point loading. The slab will continue to strengthen over the following months. It is possible to lay a floor finish such a stone bedded in a lime based product after 21-28 days but you will need to wait much longer to install a floor such as engineered wood as the moisture content will need to be much lower (2-3%)for this type of floor to prevent it from warping.

Why don’t you use a damp proof membrane?
The Recycled Foam Glass insulation layer regulates moisture. The floor is designed to be vapour permeable allowing moisture to travel and preventing it from being forced to walls.

If limecrete is laid onto a normal sub base i.e. compacted hardcore, water may be sucked into the slab by capillary action causing damp problems.

How do we mix our Limecrete and ensure strength and consistency?

We have two volumetric batch mixing trucks, Ronnie and Sally! Ronnie can hold around 8.5-9m3 and Sally can hold around 7-7.5m3 of limecrete. They mix the correct ratios of lime, aggregate and water. These ingredients are then forced through an auger to combine them. When you mix in a conventional drum mixer these different ingredients tend to ball together.

Fibres are added to increase the strength of the limecrete.

Which area do we cover?

We are based in Norfolk, but cover the whole of mainland Britain!

I saw it go wrong on TV – will this happen to me?
The near failure of this limecrete slab was the freezing weather conditions in which it was installed and the method of mixing.

We have successfully installed limecrete throughout the winter by heating the water used in the limecrete and heating the building in which it is installed. For outdoor applications we would advise you to avoid installation in the winter months.

Our mixer has been especially customised to mix limecrete.

How strong is limecrete?
Limecrete is strong enough under compression to be used as the floor slab in a home. It can be strengthened by increasing the lime content and by adding fibres. This makes it suitable for applications such as a workshop floor. The lime content should not be increased excessively as this compromises breathability.

We use NHL5 (Natural Hydraulic Lime strength class 5). We cast test cubes on site and have them crushed independently. Our data therefore reflects our work and not laboratory conditions.

What is a volumetric mixer?
A volumetric mixer measures the correct ratios of lime, aggregate and water. These are then forced through an auger to combine them. When you try to mix limecrete in a conventional drum mixer the different ingredients tend to ball together. It is tempting to splash more water in to loosen the mix the way you can with cement, but this substantially weakens the limecrete.

In what way is limecrete environmentally friendly?
The process of manufacturing hydraulic lime releases green house gases. However, unlike concrete, lime reabsorbs CO2 as it sets. As published figures vary as to how much less polluting lime is than concrete, we avoid quoting them. As the market for this product increases, the green credentials will continue to improve as production of lime becomes more efficient.

The RFG insulation is produced from recycled glass. Currently, this is imported but again, as the market increases, it will become more viable to produce it in the UK. As with any insulation, the emissions saved by reduced heat loss pays back the embodied energy of the insulation.

Can I install underfloor heating?
Yes. Limecrete is totally compatible with underfloor heating. We will be happy to discuss the insulation value of the floor with your heating engineers.

With regards to UFH do you find the slab-less design takes longer to heat given that the pipes are laid lower than laying above the slab, within a screed?

Although the depth of material above UFH may take longer to reach its required temperature. The greater Thermal Mass of the slab with ensure heat is retained.

What is the minimum depth of a limecrete floor? 

This can depend on what your architect has specified and in order to meet a specific U-Value. The minimum depth for the slab-less design that we would lay to, with UFH would be 150mm RFG and 100mm Limecrete screed.

What floor finish can I use?
Whatever you use must be breathable, stone, tile and wood can all be suitable. Please beware of non-breathable adhesives. Carpets made of natural fibres and backing with underlay such as hessian or felt are also suitable.

Can you polish a limecrete floor? 

Limecrete doesn’t naturally lend itself to being polished as once cured it tends to have small , non-structural cracks where it settles. We would recommend that either original flooring was put back or that a breathable alternative floor finish is used.

Is there a maximum thickness for the glass aggregate?

The Recycled Foam Glass aggregate that we use needs to be compacted in layers if the depth is above 300mm. The greatest depth that we have insulated so far was 550mm compacted.

Do I need to use a specialist contractor to install limecrete?
With our experience we are able to offer detailed advice and efficient service, of which we are very proud. That said, a skilled and competent builder should be able to carry out the work as long as they understand the material. If you are in any doubt, it may help to ask contractors the following questions:

  • What is the make up of the limecrete?
  • How will you mix the limecrete?
  • How long do you expect the work to take?
  • Have you previously worked with limecrete?
  • Do you have any previous customers who are able to recommend you?

What specification do you recommend for my job?
We will be happy to provide advice and a quotation. Please call us for free on 0808 168 5463 or email