Simple and robust
Lime screed is used wherever particularly diffusion-open floor structures are required. With the right floor build-up – a capillary-breaking layer of foam glass gravel, lime concrete sub-base and lime screed – moisture from the ground is buffered across the entire surface and can dry out upwards. This way it does not rise into the adjoining walls.
The strength of a screed without cement is perfectly adequate for normal living areas. Only the setting time is delayed. A little more drying time must be allowed for a lime screed. If this is possible during the construction process, such a floor – with the right floor build-up – protects the building against moisture rising in the walls.
The naturalness of the lime ensures a natural floor. The appearance and surface texture of a levelled lime floor cannot be compared with a seamless floor made of polymer-based or cement-based materials with a PU sealant.
Moisture transport
With the right floor build-up, moisture from the soil is buffered and can dry out upwards through the diffusion-open structure. This way it does not rise into the neighbouring walls.
Ready-mixed lime screed – the Kholao® range from Saint-Astier
If you'd rather not mix the lime screed yourself from NHL 5 and sand, you can turn to the Kholao® range from Saint-Astier: a coordinated system of ready-to-use lime products for floors. Mix, lay, done. Particularly practical when there is no space for a mixer and material storage, or when things need to move quickly.
KHOLAO® Béton de Chaux – lime sub-base concrete
Kholao® Béton de Chaux is the ready-to-use lime concrete for the
floor slab – the alternative to cement concrete in older buildings. It consists of natural hydraulic lime from Saint-Astier, sand and gravel (grain size 0/10 mm) and is just as vapour-permeable and moisture-regulating as a hand-mixed lime sub-base floor.
Where it is installed:
- Non-load-bearing floor slabs on the ground floor of old buildings, natural stone buildings and timber-framed houses
- Cellars, vaults and hard-to-reach areas – bagged material means no concrete mixer truck is needed
- Restoration of existing floors in historic buildings
- Indoor use only
KHOLAO® Chape – the ready-mixed lime screed
The lime sub-base concrete is topped with Kholao® Chape – a ready-to-use lime screed mortar made from natural hydraulic lime from Saint-Astier. The Chape forms the wearing layer: level, vapour-permeable and suitable for period buildings.
Unlike with a conventional cement screed, there is no need to compromise on the indoor climate here. Kholao® Chape remains vapour-open – moisture from the ground can continue to dry out, just as described throughout this page.
Suitable substrates:
- Kholao® Béton de Chaux (lime sub-base concrete)
- Old, sound, load-bearing concrete floors
- Lime-hemp sub-base concrete
Application and coating
However, the longer setting time makes it much easier to work with the screed. Levelled floors or finely rubbed surfaces are possible with the lime - but beware, the lime also sets. Don't take too much time.
Trowelled floors are incredibly beautiful, the slight unevenness and the trowel stroke that plays in the light create structures that are beautiful and unique.
We recommend applying a coat of Aglaia Aquasol stone oil as a top coat. The variety of colours is almost unlimited, from transparent to bright pink, everything is possible. The diffusion capacity is not affected and the surface strength is increased. Painting makes it possible to save the additional costs for a floor covering.
You can find everything about application in our brochure:
Cement-free floors brochure
Natural stone and lime
However, flooring on the subfloor without cement is also possible. In order not to restrict the diffusion capacity of the material, we recommend using natural stone, terracotta, limestone slabs, sandstone or slate. Here, too, there is a wide choice.
Underfloor heating is of course also possible in a lime screed. In general, installation, connection to neighbouring components and processing work in exactly the same way as with a conventional cementitious screed.
Variants of lime screed can be made by using sand. A screed of brick chippings and brick sand mixed with Saint-Astier's NHL 5 makes a particularly absorbent screed. The moisture absorption of the ground brick is very high - significantly higher than with a normal screed gravel. These floors are called Cocciopesto.
The addition of selected stones and the grinding of the not yet hardened lime screed produces a terazzo.
Wooden floorboards on lime screed: Gutshofdiele as a natural complement
For everyone who appreciates the warmth and character of wood on a mineral lime screed, our Gutshofdiele floorboards are the ideal choice. As wood itself is vapour-permeable, it works perfectly with the properties of the lime screed and supports a balanced indoor climate.
For installation, we recommend fixing the floorboards to battens to ensure even support and a stable construction. The cavities should not be left hollow – ideally, they should be filled with hemp-lime loose fill, which additionally provides thermal and impact sound insulation.
Alternatively, the floor build-up can also be made with Gutex ThermoSafe-NF. This wood fibre board offers an excellent combination of impact sound and thermal insulation and is also made from natural raw materials.
The result is a durable floor build-up made of natural materials – vapour-permeable, warm and with the unmistakable charm of genuine Gutshofdiele floorboards
Frequently asked questions about lime screed
What is lime screed?
Lime screed consists of natural hydraulic lime (NHL 5) and sand and hardens through water. It is available as the ready-mix KHOLAO Chape from Saint-Astier, to which only water is added, or for mixing yourself from NHL 5 and 0–8 or 0–16 mm aggregate with 350–400 kg NHL 5 per m³ of sand.
How thick does lime screed need to be?
Bonded to a load-bearing concrete slab at least 40 mm, floating (for example on hemp fleece or wood fibre insulation) 60–80 mm. Timber joist floors move considerably more than a concrete slab: there, lime screed is not bonded but laid floating at 60–80 mm, if necessary on a load-distributing layer of Batichanvre. The structural capacity must be checked beforehand – lime screed weighs about 115 kg/m² at 60 mm and 155 kg/m² at 80 mm.
Is lime screed vapour-open?
Saint-Astier does not state its own measured value for KHOLAO Chape; the manufacturer describes it as vapour permeable. Comparable lime mortars made of NHL 5 and sand achieve a water vapour diffusion resistance factor of µ < 8 according to manufacturer data (measured to EN 1015-19). For a screed thickness of 40–60 mm this gives a calculated sd value below 0,5 m – under DIN 4108-3 such a layer is considered vapour-open.
Can lime screed be used with underfloor heating?
Yes, Saint-Astier has confirmed this for low-temperature underfloor heating. The cover above the top of the pipes is at least 50 mm for KHOLAO Chape and at least 60 mm for self-mixed screed. First heat-up no earlier than after 4 weeks: start at 20–25 °C, increase in steps of 5 °C, maximum flow temperature 45 °C.
Does lime screed need joints?
Yes, because lime screed shrinks as it sets. Place field joints roughly every 25 m² and align them with the joints of the concrete slab below. Perimeter joints run along all walls, columns and door openings (edge insulation strip 8–10 mm) and always remain open – the skirting board covers them. With a floor covering, each field joint is continued in the covering at the same position. Only with exposed screed are the field joints closed with cork filler after at least 28 days.
How long does lime screed take to dry?
Guide values at 15–23 °C and 50–70 % relative humidity: light foot traffic after about 3 days, normal use after about 7 days, grinding no earlier than after 28 days, underfloor heating no earlier than after 4 weeks. The screed is ready for covering at a pH below 10 and a residual moisture of CM ≤ 2 %, with underfloor heating CM ≤ 1,5 %.
Should I water the fresh lime screed?
Not with KHOLAO Chape – according to Saint-Astier it does not help against cracking. Instead, protect the screed from direct sunlight, draughts and strong temperature fluctuations. The KHOLAO Béton sub-base is different: it is lightly moistened once or twice a day for one week.
Can lime screed be left exposed?
Yes, protected with stone oil. However, exposed screed is only intended for "sock areas" – living spaces where people walk barefoot or in socks. Lime screed has a lower strength than cement screed (KHOLAO Chape: class C5F1 to EN 13813). For more heavily used areas we recommend a covering of natural stone or terracotta.
Which floor coverings suit lime screed?
Absorbent coverings such as terracotta, brick, slate, travertine and limestone, laid with KHOLAO Colle and grouted with KHOLAO Joint. We do not recommend glazed or dense ceramic tiles, because they prevent moisture from escaping upwards.
How do I build a lime floor on soil?
From bottom to top: foam glass gravel 20–30 cm, compacted; KHOLAO Béton sub-base at least 15 cm; hemp fleece 5 mm (wet it beforehand); lime screed 40–60 mm.
What should I do if cracks appear?
Open the crack with an angle grinder and fill it with a slurry of NHL 5 and 0,3 mm marble sand. If there is no joint at that point, for example at a door threshold, cut one afterwards – simply filling the crack is only cosmetic.