Recently I have been experimenting with Hempcrete as a sustainable wall panel system for my Dom-Into house project. It is very simple to make, has great thermal properties and allows a building to breathe.
Hempcrete primarily is used in wall, floor (slab), render/plaster and roofs. In a roof, insulation is an important aspect so low density (light weight) is used, whereas for additional structural strength, high density hempcrete (low thermal insulation) is used in floors. Natural breathable finishing (lime render and plaster and mineral based paints) are commonly used in hempcrete walls. However, if cladding is used, a breathable one with vented air gap in between the wall and cladding is better. Lime-hemp plasters and Hemp-fiber quilt insulation are other uses of hemp in construction industry. In my Dom-Ino house I investigated usuing hempcrete for insulation to floor slabs and ceilings.
I used just hemp shiv, lime and water. The frames and base were made from MDF. The Mixture is easy to do, just weigh the dry ingredients and mix very thoroughly, then add the water and again mix very well. Use a mask, gloves and eye protectors when you are doing the mixing as the lime is toxic and can burn your skin/eyes/lungs.
Once it is mixed, add into moulds and tamp it down firmly, and then leave to dry. It takes 12 hours to dry out these brick sizes shapes.
MAKING HEMP MIX:
I made 3 batches of hemp mixture using different ratios of lime to shiv to water – the graphic above has the ratios needed, and the binder is pure hydraulic lime.
Batch 1 was the best consistency – heavy but strong and not crumbly.
Batch 2 mixed cork granules with the shiv to see if I could create a lighter weight to the mix. This was successful, but I think the lime mortar ratio could be upped to bind it better.
Batch 3 was very crumbly and loose and not a strong material for construction.
The results were really good, with the bricks being lightweight and strong. For houses, larger panels tend to be made by using shuttering and then by strongly tamping down the mixture.