The lightweight breathable alternative to concrete

The advantages of Limecrete

• Increased vapour permeability
• Can be mixed with LECA to provide an insulated floor
• Can be designed to meet the needs of the building

A typical limecrete installation

• Levelled compacted ground
• Breathable membrane
• Loose fill LECA 10-20mm coated for reduced capillary action
• Breathable membrane
• Limecrete based on 3 parts sharp sand/aggregate to 1 part St Astier NHL 5
• Lime screed based on NHL 5 and sharp sand.

Limecrete can be made with LECA in the mix instead of sand/aggregate.

A limecrete floor can then be finished with flagstones or breathable tiles.

Underfloor heating can be installed in the lime screed – see manufacturers specifications.

Site-mixed Limecrete for Floors, exposed aggregate / tamped finish

Ingredients

400 KGs St Astier NHL 5 per cubic metre of aggregates consisting of 1 part sharp sand: 2 parts 12 - 18mm aggregate and approximately 5 - 6 litres of water per 50 KG of lime.

Mixing Limecrete

Mix dry to achieve a uniform colour in a pan mixer or roller pan mill, slowly add clean water until semi dry, just sufficient to allow mix to bind when squeezed in hand. Free fall mixers can cause balling.

Substrate

Limecrete should be laid on a compacted sub base of clean 75-50mm screened aggregate (150mm minimum). The greater the thickness of the sub-base, the better the insulation properties.

Damp proof membranes are not necessary. Limecrete can be laid directly on to sub soils that contain clays that have had a 20mm layer of St Astier NHL 5 hydraulic lime rotovated into them and compacted (sub soils should be analysed before proceeding). Damp proof membranes are not necessary.

Laying Limecrete

The concrete is placed in a single layer of 50mm, or 2 layers of 50mm to make a 100 mm layer depending on purpose. 50 mm will be sufficient for normal foot traffic and 100mm for light vehicular traffic. It should be well rammed either by hand or with a mechanical compaction plate to the desired level. Form mechanical key between layers. Lay green on green (within 24 hours).

Finishing

Exposed aggregate finish: after 24 hours the surface of the compacted and levelled concrete is brushed with a stiff yard broom initially, then a soft brush. On large areas it may be necessary to treat the surface of freshly compacted concrete with an inhibitor to hold back the set.
A trial panel should always be done.

Curing

Light mist with clean water for 72 hours or more depending on conditions.
Never lay on a frosted or exceedingly hot surface. Protect from extreme heat, freezing, excessive wind, strong direct sunlight and rain. Ambient temperature range should be 5oC-30oC with low to average humidity.

Protection

Foot traffic should be avoided for 7 - 10 days depending on the weather. Cover with protective walkways 12 hours after placing. These should remain in place for at least 2-3 weeks or longer if possible.

Natural Limecrete screed for heated floors

The limecrete has to reach a density of above 2200 kg x m3.

To achieve this use an aggregate of 10mm down to 0.150.

You might have to mix 3mm down, well graded sharp sand with fine gravel (up to 10mm) in a 50/50 mix. The dosage of lime (NHL 5) will be 400/450kg. per m3 of aggregate (1:2 by volume).

80mm thick screed: lay first 40mm (semi dry mix), level and compact well. Cure for 1 week with light water mist 2 times a day. Once sufficiently hard fix the heating elements on this layer. Put heating elements under pressure to check for leakages. Once satisfied that there are no leakages,
apply the remaining 40mm of mortar, level and compact. Light spray the surface with clean water as soon as you have finished to compact.

Curing: with a light water mist 3 times a day for at least 2 weeks.

Do not use heating for minimum 3 weeks.

Natural Limecrete for Fine / Ruled Finish Floors

Ingedients

400 KGs NHL 5 per cubic metre of aggregates consisting of 1 Part sharp sand: 2 Parts fine sharp sand.

Mixing

Mix dry to achieve a uniform colour in a pan mixer or roller pan mill, slowly add clean water until the correct moisture is achieved (semi dry) just sufficient to allow mix to bind when squeezed in hand. Free fall mixers can cause balling.

Laying

The concrete is placed in a single consistent layer of 10 to 25mm. It should be well rammed either by hand or with a vibrating screed to the desired level. Lay green on green.

Finishing

Tighten in the surface with a cross-grained wood float to a level plane, polish after initial stiffening with a steel float if desired. Lining out or ruling after 12 hours. A trial panel should always be done before attempting large areas.

Curing

Very light mist with clean water in drying conditions for 72 hours.Protect from extreme heat, freezing, excessive wind, strong direct sunlight and rain. Ambient temperature range should be 5oC-30oC with low to average humidity

Protection

Foot traffic should be avoided for 7 - 10 days depending on the weather.

Cover with protective walkways 12 hours after placing. These should remain in place for at least 2-3 weeks or longer if possible.

Limecrete sub base for slabs using St Astier Natural Limes

Ingredients

200 KGs NHL 5 per cubic metre of well graded sharp sand 6mm to 0.075mm

Mixing

Mix dry to achieve a uniform colour in a pan mixer or roller pan mill, slowly add clean water until the correct moisture is achieved (semi dry), just sufficient to allow mix to bind when squeezed in hand. Free fall mixers can cause balling.

Substrate

Outdoors: lay on a compacted sub base of clean 50mm screened aggregate (75mm minimum).

Should a membrane be required use a geotextile (not polythene).

Indoors: lay on a compacted sub base of clean 75-50mm aggregate (100mm minimum). The greater the thickness of the sub-base, the better the insulation properties. Damp proof membranes are not necessary.

Laying

Placed in a single layer of 50mm. It should be well rammed either by hand or with a mechanical compaction plate to the desired level.

Form mechanical key and lay a further 20mm layer loose ready to set down slabs. Lay slabs as normal.