Hempcrete – Hemp lime construction 

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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 known 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 lightly tamped as in-fill material between temporary shutters or packed as blocks 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. 

 

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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 highly fire resistant, passing local SABS 2-hour fire tests. 

 

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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. 

• Alternately one can purchase or make light weight blocks that are stacked between timber stud supports. 

• In Europe hemp shiv is mixed with a fast-setting Hydraulic lime. 

• South Africa does not have sources of hydraulic lime. As such a small amount of cement or a mix of furnace slag and meta-kaolin 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. 

 

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Track record/examples of work 

• House McMichael, Scarborough, Cape Town, 2022-23 

• Voluntary building participation at Yiza Ekhaya Soup Kitchen, Kuyasa, Cape Town 2015 

• Council plans for Wolf & Wolf Architects for House Wolf, Bokaap, Cape Town 2014  

• Alts & Adds to House Louw, Rondebosch, 2014