The surfaces of walls or wood-frame walls with hemp concrete must be prepared in advance for insulation.

For wood-frame walls:

Nail a baton at the centre of the wood frame wall. If the wood-frame timbers are more than 60 cm apart, fix one or more batons between them. On the inner side, cover the wood parts with a minimum thickness of hemp concrete. The outer side must be covered with protection (panelling, rendering, etc.). You may need to leave a reentrant of 15 to 20 mm for finishing render. Do not use exposed hemp concrete on both sides of an external wall. Do not use exposed wood frames on both sides of the wall.

For poured-concrete walls:

If the masonry is in place and on a clean, solid support, apply a roughcast at first, 1 volume of Prompt natural cement for 2 volumes of sand, and insert service ducts in advance.
In the case of a wood frame, it is important to apply a minimum covering of hemp concrete. Insert service ducts beforehand. The covering of timber elements depends on their thickness. The coating must be at least 7 cm. Timber elements in excess of 8 cm can be left exposed.

Application:

Very damp areas are not recommended, and a damp course must be left between the basement wall and the hemp concrete. Leave ground clearance of around 20 cm. Hemp concrete must not be used on poured-concrete walls during frost or in strong, dry winds.

Doses:

Application:

The mixture must be homogenous, with the binder covering the beam well, without lumps. The open time is approximately 15 minutes, depending on the recommended Tempo doses. Position the form work, with respect to the required thicknesses and leaving a 1.5-2 cm reentrant for render if this is to be applied on bare wood. The recommended height of form work is 15 to 18 cm. For hemp concrete in successive layers of 10 to 15 cm, chase the whole surface, and slightly compress the edges of the form work and wood parts. Add another layer, and so on. As soon as the form work on the filling side is full, raise the form work by sliding it without unfastening it. The form work can be removed immediately the concrete is set, for optimal drying.

 Technical characteristics:

• Density: 450 to 550 kg/m³  according to settling
• Compressive strength >0.2 MPa
• Thermal conductivity 0.07W.m-1K-1 at 0% relatively humidity

Thermal resistance:

Depending on settling, the following is required for each 1 m³  of hemp concrete:

• 1,150 to 1,300 litres of Hemp Granulate
• 280 to 310 kg of Prompt natural cement

The finishing coat should be applied after drying. Drying time depends on the ventilation of the premises, air humidity and the thickness of the concrete.
For example, drying time for a thickness of 15 cm varies from 30 to 60 days, depending on local conditions. Hemp concrete’s permeability to water vapour must not be compromised, and for this reason at least one side must be covered with a coating that is permeable to water vapour.

Consult our Application Guide, available for download.