Eco construction


Concrete base

Two types of concrete base may be made:

  • slab on an earth platform: a telford base must be systematically laid to allow the slab to breathe and prevent water rising through capillary action. Composition of the telford base: 1 x15 cm layer of thick large stones, grade 40/70 and 1 x10 cm layer of stones, grade 20/40. Install 10 cm drain pipes transferring the water outside the walls.
  • Light concrete base: the lightness of hemp concrete allows it to be used for upper floors during renovation. 2 cm of hemp chaff, dusted with Prompt natural cement, are poured to allow the base to dry without any humidity transfer to the wooden floor. Do not use water vapour impermeable film on wooden floors.


Precautions measures: use between 5 and 30°C.

Dose for information:

Building Hemp Granulate PNC Tempo Water
100 litres 30 kg (1 bag + ½ bucket) 1 bottle 25 l (mixer) or 27 l
(concrete mixer)

Use concrete mixer or ordinary mixer.


The mix must be homogenous, with the granulates well covered by the binder, with no lumps. The open time for the mix is approximately 15 minutes, depending on the recommended Tempo doses. The first 5 cm-thick pass is levelled off with the rake and then smoothed by foot. The following passes are smoothed with the rake and then floated or compacted slightly so as to not reduce thermal and acoustic performance. This application is easier in 2 strips of 1 to 1.2 meters width. The slab can be walked on the same day. A planked-out route may be necessary in case of intensive use. The minimum thickness of the slab is 10 cm.

Technical characteristics: 

  • Density: 500 to 600 kg/m3 depending on earthworks.
  • Compressive strength: > 0.3 MPa
  • Thermal conductivity: 0.07 W.m—1K-1 at 0% relatively humidity.

Thermal resistance:

Thickness (cm) 10 15 20 25 30
R (m²KW-1) 1.40 2.10 2.85 3.55 4.25

For each 1 m3 of hemp concrete used, 1,100 to 1,200 litres of hemp granulates and 330 to 350 kg of Prompt natural cement should be used, depending on earthworks. Before the covering is applied, ensure that the slab is completely dry. Drying time depends on the ventilation of the premises, the rate of humidity and thickness of the slab: a 12 cm-thick slab takes around 30 to 60 days to dry. All coatings must be permeable to water vapour.

Consult our Application Guide, which is available for download.