Having learned, in 2002, about how to mix and use hemp and lime as a breathable material for building walls I decided to use the technique on a dwarf wall underneath a wooden conservatory. The method and materials were the same as used in the housing association demonstration building in Sudbury which was based on French chopped hemp and know how.
A substantial stud frame was built as the structural load baring element on a concrete foundation with a course of brickwork at the base. Then chip board formers were cut and attached to the frame with wooden spacers to allow the hemp and lime mix to be troweled in to cover the stud frame.
A mix of of hemp shive, hydraulic lime and sand and mixed in a cement mixer to form a porridge consistency. The mix was troweled into the former and tamped down and allowed to build up. Care was needed not to get it between the gloved hands and the overall cuffs as the mix is very alkaline and can burn your skin.
I understand that the hemp and lime is solid enough to remove the formers from after about 24 hours but actually to ensure the mix had done off they were left on longer.
When the formers were removed and the conservatory top built the walls were covered with a lime scree and lime washed to match the rest of the house. The floor area was built up with a layer of pea gravel and a hemp and lime mix, quarry tiles were laid in a lime mortar slurry which bonded much more effectively than a thicker lime mortar.
After the conservatory was built it has proved to be warm and pleasant to sit in – however the wall is only a small component of the whole building here. The exterior walls have to be lime washed quite regularly about once a year – but this is a quick job as the wall isn’t big. The main advice is to make sure there is no chance of moisture getting into the hemp and lime mix once set as it can attract insects that like any moisture on the top surface of the hemp.
Technology has moved on since this wall was built and Lime Technology Ltd. in Oxfordshire have got commercial materials ( such as Tradical and Hemcrete) and methods for building hemp and lime buildings. Hemp and lime has been used for some fairly substantial buildings such as Adnams Brewery warehouse which has a double hemp and lime wall helping to act as means of temperature control without refrigeration – saving money and energy.
Andrew Ormerod, 2014.