Wednesday 3 December 2014

The first hempcrete mix

If you'd asked me where the first mix would be placed, I can't imagine that I would have said under the box gutter. Luckily, I spent some time chatting to Wayne the plumber about our storm water layout, and he explained the sequence for installing the roofing and guttering. Turns out that the box gutter had to go in before the rest of the roof could be completed.

I had hoped Wayne would get the remainder of the roof on before the material was delivered, and the only weekend available beforehand was the weekend that I was also helping out on a Cub Scout camp. So the first mix was shaping up to be a rushed affair. It was Sunday lunch time before I could make a start.

As we didn't have any MgO board for the ceiling yet, I decided to install a temporary formwork to hold up the hempcrete. I would have to take it down after curing, so just in case the hempcrete did not support itself, I stapled some hession under the rafters first. A good move as it turned out.


It wasn't until we were all set up that I realised we didn't know the ratio of hemp, lime and water for the ceiling mix. I had the instructions for wall mix, but not the ceiling mix. Pity it was the weekend.

I reasoned that if the ceiling mix only used half the lime, then I would only need half the water. I reasoned wrong! It was pretty clear that the mix was too dry, so after a mild panic, we quickly tossed in an extra 1 1/2 litres. It seemed that the mix was holding together a bit better, so we placed it.

Sam worked the mixer, and Shelley helped move the tub of mix. First mix, first accident. The handles of the tub weren't strong enough and a tub load narrowly missed Shelley as it tipped out all over the floor.

Otherwise, everything went smoothly and we mixed 2 1/3 bales of hemp. It's now over a week since the hempcrete was placed, Wayne didn't make it to finish the box gutter, so I checked it out. It's a bit friable on top, but it has bound together somewhat. The big test will be when I try to remove the formwork below, but that won't be for some time yet. Meanwhile, I hope the plastic will keep tonight's rain off our first attempt.

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