Hemp is a plant in the Cannabis family, grown for its fibre. It has negligible psychoactive (drug) properties. The fibre from this plant has many uses, including the manufacture of fabrics and some papers, while the oil from the seeds is used as the base of some oil paints and in moisturising creams, etc.

In renders, hemp is used with lime to reinforce the render and prevent cracking due to drying, while the lime effectively preserves the hemp fibres in the mix. These renders also have much better insulating properties than traditional sand and cement renders, thus adding to the insulation value of the wall. The other main advantage of these renders is their breathability, meaning that moisture vapour can move through it, effectively keeping the substrate dry. The render is generally applied in a couple of coats and total thickness is usually 20 – 30mm. These renders can be used both inside and outside, typically utilising finer fibres for the internal renders to give a smoother finish. These renders need to be handled and cured in much the same way as hydraulic-lime renders.

Aidan O’Brien of Ecobuild Ireland Ltd has used this render in the Ecovillage project in Cloughjordan, Co. Tipperary, which we were involved in. He looked at the possibility of growing the hemp local to the site and producing the hemp-lime render as simply and cheaply as possible, to make it more sustainable, as much of the hemp used in this country was previously imported from France. However, hemp for a number of construction uses, as well as hemp-lime, is now available from Hempire Building Materials Ltd. in Co. Monaghan, using hemp grown in this country.

Hemp and lime can also be mixed to create a type of concrete from which walls can be built and which have their own inherent insulation. This is generally placed between formwork or into a permanent timber frame, and plastered thereafter. These walls also have significant thermal mass, allowing the walls to store heat at hotter times, e.g. during the day, and releasing this heat at cooler times, e.g. at nighttime. Aidan O’Brien of Ecobuild Ireland Ltd has also built some houses using this product. One client is using bricks he is making from this material to place within internal stud walls to give the walls thermal mass and to reduce noise transmission between rooms.

For photos of these products, click here.