Hand applied hempcrete interior thermal insulation.


Hempcrete has excellent thermal insulation properties and also is breathable to moisture. In several volunteer sessions we have applied about 20mm of helpcrete to the tyre walls. It has a lovely finish as it follows the pregnant curves of the tyres.

As the need to insulate the walls of conventional British houses becomes more pressing the use of hempcrete is likely to become more widespread. Emma Winfield of Real Refurbs is doing some tests of internal hempcrete insulation in 2012. SHe's loking at what happens where the hempcrete meets the floorboards or joists.

In my case the insulation is required as the design of the tyre wall I used lacked thermal insulation between the bottom of the wall and the top of the foundations. This means the wall can act as a thermal sink - draining heat from the room into the floor void. The hempcrete is designed to reduce this effect.

Here's the Bristol Green House hempcrete recipe, based on our experimentation over several days.

By volume:
2 hemp
1 hydrated lime
0.5 NHL
1.25 water

A mix takes about 40 minutes to go smooth. We put all the dry material in then covered the opening of the mixer with plastic so the lime could coat the hemp. After letting it settle for a couple of minutes we gradually added the water. One 25kg bag of NHL will do about six mixes when the units used are buckets full.

If ordering the hemp direct from Hemcore (in the UK) don't tell them its for making hempcrete. They are the only UK supplier of hemp and the makers of their own proprietry hempcrete (which contains cement!).



Masks should be worn if mixing your own hempcrete. The lime dust is not good to breath in.

Above shows the rough finish of the first session. I always assumed I was doing a second coat so left the finish rough. Below shows a more worked finish. The volunteers I worked with in 2012 had an artists amongst them and he perfected smoothing the surface by patting and gently rubbing with a wet gloved hand.

Photo:Simon Cochrane



Photo:Simon Cochrane

The truth window reveals car tyres and tin cans

Photo:Simon Cochrane

Usually hempcrete walls are made using shuttering so I tried one small area (above). We buried bottles to reduce the volume used.

Photo:Simon Cochrane

The reward for generous volunteers on our project is always delicious food cooked by my wife Sally.