Okay this could be long winded but hopefully I can get the picture for you all.
Firstly for clarity, hempcrete is a generic term for an old basic recipe of lime, hemp & water that has been used for decades in Europe for the restoration of old wattle & daub or cob construction. Have a look at "Tom Woolley - Hemp lime construction. A guide to building with hemp lime composites". Unlike concrete or masonary, hempcrete does not crack severely under movement. Lime is weak under tension and develops micro cracks under movement that heal when it gets moisture. Concrete or masonary will let go suddenly under movement which is why you get big noticeable cracks.
Tradical Hemcrete is a hempcrete mix using a proprietary lime binder Tradical HB with hemp chips that has commercially-defined properties and British certification. This is what I am promoting. Hempcrete can be used but its properties are not commercially "proven" which is harder to get passed. Having shown building certifiers, they don't have a problem under the "Deemed To Satisfy" provision of the BCA. We have just had a building certifier approve for construction a house in Tasmania - the energy efficiency auditor using AccuRate gave it a 6.4 star rating and apologised cause the software wasn't good enough to achieve higher in Climate 7 region. He felt we could get 7 star with a more complicated commercial software that could better accommodate some of the beneficial properties such as airtightness(depending obviously on glazing used).
So how do we use hemcrete? This is monolithic construction - solid wall. Hemcrete is not runny like concrete - the best description I've heard is that it's like elephant s##t, you have to squeeze it hard to get water to run out. So it's damp but not wet therefore most machinery like concrete pumps cannot work it because lime sticks to anything and blocks too quickly. It can be made into blocks although it increases costs and embodied energy dramatically, does not provide as good airtightness and will be a more dense mix thereby not providing the best insulation values.
Hemcrete is deemed non-structural although it has small loadbearing capacity. Therefore you build a frame (preference is for timber - no thermal bridging) to do the structural work ie the backbone. Services are then positioned as normal. You shutter approx. 1.2m up around the entire wall frame - the shutters can be 6-9mm ply since there is no hydrostatic pressure on it. The thickness is solely to keep it straight. If you frame the shutters at 450mm centres, you can use 4mm ply (it does work!).
"Pour" the hemcrete in and encase the frame. Imagine a BV house frame - remove the BV and replace the entire space with hemcrete to 250mm (you don't need the void), that's what it would look like. After a day's pour, next morning you strip the shutter and go 1.2m up and do it again. Hemcrete will not slump.
The frame can be located to one side of the shutter for ease of fixings or centrally located in a 250-300mm wall to allow services along the frame rather than through it.
Right now, the proven method to 'pour' hemcrete is by bucket! Now before you go nuts, hemcrete is about 1/8th the weight of concrete at 330 kg/m3 therefore a wheelbarrow load weighs no more than 15 kg and a 15L bucket only 5 kg. You'd be amazed how much you can get done since it's light to work with. When you pour it, you lightly tamp to give it structure into joints and around the timber.
Hemcrete needs to breathe (vapour-permeable) to perform well in damping humidity and temperature. You can render it with a lime render externally or batten it so that there is an air gap between the non-breathable cladding and the hemcrete. No need for sislation. We are looking to use a breathable (vapour-permeable) board like Magnesium panel to internally line the walls therefore achieving a breathable skin that can look like normal finishes. Mag board can be used externally as well. The paint needs to be vapour permeable as well.
We have a 1m high x 1.4m long x 250 thick wall that has been outdoors unfinished for 21/2 years now - there is no mould, it has bleached and has not degraded so it is durable.
Last but no less important, cost-effectiveness. It is cheaper than Hebel blocks - taking into account timber framing, it probably works out around the same price but the performance is far superior. Right now, we are prototype testing a high volume sprayer that will make hemcrete a very viable commercial product for large and small scale projects. Until this has been fully developed, I believe hemcrete best suits owners, owner-builders and builders that place thermal performance above low cost such as people in this forum.
As a fence, you could put it up without a finish. I would make it really dense tho to handle any impacts. Mind you, if it gets damaged, you scoop up the damaged pieces add a bit of binder and re-use it to repair. No waste, totally recycleable.
I am based in Brisbane so if you want to chat call me on 07 3324 9770 or 0438 006 059. Just ask for Davide.
Posted Wednesday 26 May 2010 @ 2:03:50 am from IP
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