Limecrete FAQ

Frequently asked questions about limecrete

What is limecrete?
Limecrete is a combination of natural hydraulic lime and lightweight aggregate 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.

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 temperature. It is possible to move over the floor using boards after a few days but we would not recommend this due to the possibility of weakening the slab. A slab strengthened with fibres is generally safe to walk on after a week but will continue to strengthen over the following months.

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.

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 in 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.

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.

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, any 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 is the floor insulated and what U value will be achieved?
  • How will damp be controlled?
  • How will you mix the limecrete?
  • How long will the work take and how will you deal with joints?
  • Do you offer a guarantee?

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 sarah [at] limecrete.co.uk