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Hempcrete – Hemp lime construction

Background:

  • First used in France since the early 1990’s and developed around repair work to old medieval timber frame wattle and daub structures.
  • A mixture of the woody inner part of hemp stalks know as shiv and an hydraulic or fast setting lime is mixed with water and used as a non-load bearing in-fill material and can be used for the construction of walls, ceilings and roofs
  • It can be used for both internal and external walls as well as for ceilings, and is commonly compressed between lightweight timber frames.
  • Historically Japan has a century’s old tradition of using the finer hemp fibres in the recipes of their traditional lime and clay plaster finishes.

Benefits:

  • Hempcrete can be used to make pre-fab blocks, as an insulating base plaster or sprayed-on material, but is most typically poured manually into a wooden construction for a high performance plastered masonry wall effect with a seamless result.
  • While the material sourcing currently has challenges, it is a simple building process requiring fairly basic skills and tools.
  • Creates high levels of thermal and sound insulation. The material is lightweight so good for alteration works.
  • The material offers a healthy indoor environment as being vapour open it works as a phase change material helping balance out indoor humidity levels.
  • It is also fire, wind, rot and fungi-proof.
  • The timber and hemp that is trapped in the walls along with the lime as it carbonates, effectively become a form of carbon sink and so helping he construction be more carbon neutral.
  • Technical Information:
  • Typically used non-structurally as a fill material, it is mixed on site, poured between shutters and then lightly tamped around a lightweight timber framing structure.
  • Shutter work is temporarily fixed in position to the timber framing.
  • In Europe hemp shiv is mixed with a fast setting Hydraulic lime.
  • However, South Africa does not have sources of hydraulic lime. As such a small amount of cement or mix of furnace slag and metakaolin or other pozzolanic admixtures are needed in the mixture to facilitate a faster setting process.
  • Officially most hemp is still imported, with a limited number of temporary growing licences having been issued to date, with only rudimentary processing methods being employed.

Track record/examples of work

  • Yiza Ekhaya Soup Kitchen, Kuyasa, Cape Town 2015 for Wolf & Wolf Architects
  • House Wolf, Bokaap, Cape Town 2014
    Stage 4 Approval for Wolf & Wolf Architects
  • Alts & Adds to House Louw, Rondebosch, 201