Limecrete – the vapour permeable solid floor

Limecrete Limecrete is a modern interpretation of a traditional solid lime or gypsum floor that can still be seen in many historic or well preserved older homes. It has also been used to create limecrete buildings with limecrete shuttered walls. Limecrete, known as green cement in the USA in the United Kingdom is normally used to create an alternative to a concrete floor with or without a DPM (Damp proof membrane).

It is vital to have an alternative option for a traditionally built house as an impervious, non flexible cement floor may create problems with dampness being forced into the walls at ground level which can result in poor insulation, mould growth with associated health problems and even structural damage. Many conservation officers with responsibility for listed buildings would encourage the use of the limecrete option rather than the less flexible and non-vapour permeable concrete floor build-up required by Building Regulations.

Limeash floors were originally made with lime putty and lots of a pozzolanic additives to provide an hydraulic and hard set. Although very effective, this method needs a very long time to harden and carbonate. A Limecrete floor is made using a natural hydraulic lime (NHL) powder that sets much quicker and potentially harder than the limeash floor. A mixture of NHL5 and well graded aggregates can be used to create the limecrete slab but it is also possible to introduce breathable insulation using an insulating aggregate and even underfloor heating.

Traditional BuildingThe image above shows what can happen to a traditional house when modern materials are used. Modern materials should normally only be employed in houses designed with these materials originally.

‘Like for like’ is the phrase that should be borne in mind when undertaking repairs, renovation or maintenance.

Insulated Limecrete floor

Mike Wye & Associates Ltd. offer an option for an insulated floor using an insulating clay aggregate. This can be incorporated into the slab rather than using sand and in it’s coated form it can be used as an effective loose lay material below the slab to help prevent capillary action pulling moisture from the ground.

Limecrete floor cross section plan

Limecrete offers a number of advantages:

  • increased vapour permeability, which is important in older properties
  • hydraulic lime is more environmentally friendly compared to cement
  • it can be designed to meet the insulation requirements of building regs

Our friendly and knowledgeable staff offer advice on the design of limecrete floors and then can work out the material quantities for your project. We provide a full service from design through to despatching the materials to any location. We do not charge for the calculation service.

As a major supplier of both the insulating aggregate and NHL we offer unbeatable prices, please see the following links for method statements for laying an insulated limecrete floor or a lime concrete floor using sand

Below is a new concept in vapour permeable solid floors. Developed by Mike Wye & Associates, the Nocrete floor uses Technopor for the looselay capillary break and thermal insulation, with cork boards laid on top for the main insulation. Nocrete give the very best insulation values therefore reducing the amount of labour and spoil as it limits the amount of digging out. Most importantly, it reduces the chances of damage to foundations saving potentially catastrophic issues

Currently, some builders are installing shallow limecrete build-ups with under floor heating (UFH) as a compromise for lack of foundations. This costs the home owner much more in heating costs as long as the system is installed. Nocrete floors allow the UFH pipes to be quickly and easily clipped to the cork boards. This is a cost effective option for any traditional building.

Nocrete floor

Mike Wye & Associates provide a free guidance and quotation service for materials that can be supplied anywhere in the UK. We also offer a fitting service in the South West by our experienced team of conservators.

For more information see the information below for the materials, potential u-values and example limecrete build-ups.

Natural Hydraulic LimeSecil for prices please click here

Secil NHLs have been available since 1891 and have made a huge contribution to the construction market in Portugal. Secil and Mike Wye & Associates have joined forces to provide Portuguese natural hydraulic limes to the UK.

We believe these will offer an excellent and cost effective option for those wanting to use powdered hydraulic limes in their work, particularly for the ever growing limecrete market where NHL5 is widely used. Secil NHL5 is fast setting and ideal for limecrete floors whether used with sand aggregates or insulating aggregate such as ‘light expanded clay aggregate’. The Secil NHL has a similar strength to the French NHLs.

For NHL brochure (PDF format) click here
For product sheet (PDF format) click here
For Health and Safety Sheet (PDF format) click here

Secil NHL5 Click here for technical sheet

Normally used for flooring such as limecrete floors or for highly exposed situations such as chimney flaunching etc.

Natural Hydraulic LimeHanson-Castle for prices please click here

We are Main Distributors for Castle Natural Hydraulic Limes, recently rebranded as Hanson lime. These powdered limes come in three grades – NHL 2 ( feebly), NHL 3.5 (moderately) and NHL5 (eminently) hydraulic. These quality NHLs are made in France and fully meet the requirements of BS EN 459:2001. Natural Hydraulic Limes are mixed with a suitable sand to make hydraulic lime mortars which set in the presence of water – hence the term hydraulic. These French hydraulic lime mortars are relatively quicker setting and have a higher final setting strength compared to the UK NHLs and therefore they are more suitable for exposed environments.

They are supplied in 25kg moisture resistant bags and due to our bulk purchasing power we can offer unbeatable prices.

For Technical Sheet (PDF format) click here

For Health and Safety Sheet (PDF format) click here

Lightweight insulating clay aggregate for prices please click here

The expanded clay aggregate consists of lightweight, porous, ceramic granules formed by expanding special clays at high temperatures. The coated version of the aggregate is free-draining and has negative capillary action, good load-bearing properties and good thermal qualities (k = 0.10 w/mk), and is used as an insulating layer below the limecrete slab. This is a vital part of the build-up of a limecrete floor, offering an effective vapour permeable barrier to excessive moisture levels. See the graph image below of the test results. This shows that a minimum of 120mm is required for an effective capillary barrier.

limecrete graph

Water suction height above water surface and moisture content in kg/kg for the individual layers


The uncoated aggregate is mixed with NHL to form a limecrete slab – we recommend Secil NHL5 for this slab.

Bulk discounts are available for 10 plus bags of 1.2 cu.m or 1.9 cu.m sizes. Bulk discounts for multiple pallets of bags are 2-3 pallets = 5%, 4 or more pallets = 10% – Clay aggregate can be supplied in loose bulk lorry loads for extra savings .

All prices are plus carriage, although the 50 litre bags are available ex-works. The weight varies due to the variation in moisture content.

Technopor foam glass aggregate
Technopor prices * Technopor installation instructions * Technopor Design data * Technopor Carbon footprint * Technopor Brochure

Technorpor lightweight looselay insulation for limecrete and other applications

Technopor foam glass insulationTechnopor is a lightweight, breathable looselay aggregate made from recycled glass. It is used in the same way as the coated clay aggregate but differs as it is capable of being used as a load bearing hardcore and has better lambda value, so needs less depth.

Lambda thermal conductivity of around 0.08, this has about 30% better thermal performance than the clay aggregate.
Technopor loft insulation Technopor limecrete insulation Technopor flood protection Insulating a basement room with Technopor



 Looselay loft insulation

Looselay loft insulation

Technopor base with geotextile membrane

Technopor base with geotextile membrane

Dealing with flood prone buildings

Dealing with flood prone buildings

Below ground uses

Below ground uses







At just 1/10th the weight of gravel, Technopor foam glass is very lightweight, it is Fire resistant being in compliance with Euro class A1. Technopor is very stable and is load bearing with an exceptional compressive strength of approximately 500kN/m2.

The foam glass aggregate is around 30 – 50mm grain sizes and needs to be compacted by wacker plate if being used as flooring or foundations. You should allow up to 30% extra volume when calculating for a compacted application. If used as a loose lay in a loft or under a suspended floor, then no compaction is required.

Geotextile Membrane for prices please click here

This vapour permeable, geotextile membrane can be used for gardening or landscaping purposes. We supply it for use in a build up for a limecrete floor. It comes in a 4.5m roll so we cut it down into linear metre lengths as required for ease of carriage.

Guidance on Thermal Values

The insulating clay aggregate has a K-value thermal performance of 0.1W/m2k. The greatest insulation is provided by the looselay beneath the limecrete slab as mixing with a binder reduces the thermal performance.

The clay mixed with NHL5 is currently not certificated but a mix with cement has been and offers a k-value of approximately 0.2 W/m2k. The figures from this might reasonably be extrapolated and used as an assumption of thermal performance when mixed with NHL5.

The 2006 revision of Part L Building Regulations specifically allows a get out from the regulations if those regulations are contrary to the well being of a traditionally built property. For example, a damp proof membrane or excessive depth of insulation required to meet Part L undermining the shallow foundations.

Example of difference that oversite and substrate make

of oversite (m²)

Depth of coated clay insulation loose fill required (mm)
or Gravel
– 50
200 210 210
– 100
180 200 210
– 150
150 190 210

Using the K-values as above, here are some examples of u-values that may be achieved using different depths;

100mm of limecrete slab with 200mm of loose clay = 0.39
100mm of limecrete slab with 300mm of loose clay = 0.28
100mm of limecrete slab with 400mm of loose clay = 0.22

It is important to match the design of the limecrete to the needs of the building. Factors include the type of construction for both floor and walls, floor area and groundwater levels.

The thickness of each component depends on a number of factors on which we can advise. Some installers use NHL 3.5 which is moderately hydraulic compared to NHL 5 which is termed eminently hydraulic. NHL 3.5 based limecrete may take much longer to cure than NHL 5 and this will be an important consideration in winter working.

Example Specification
1. Levelled and compacted ground
2. Layer of geotextile membrane
3. Loosefill. A 220mm layer of loose fill 10-20mm coated clay insulation
4. Layer of geotextile membrane
5. Limecrete slab 3 parts clay aggregate 1 part NHL5 by volume at 100mm
6. Optional 75mm screed of 2 parts aggregate 1 part NHL5 to bed heating pipes
7. Bedding screed 20-50mm of 2 parts aggregate to 1 part NHL5 to bed choice of breathable flagstone, tile etc.
8. Grout with 2 parts aggregate to 1 part NHL of choice for colour

NB. 11-13 x 25kg bags NHL5 to 1m3 clay aggregate will cover 100m2 at 10mm depth

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