Hemp Test Building: Coming out of the ground



This article relates to the early construction stages of our hemp test building, described in the previous post An experimental project is born.

We took down an existing shed and we broke up the slab for re-use as hardcore under the new structure. We’ve tried to re-use as much as we can or save materials, like end-of-line bricks, from land fill.


End-of-line bricks: as there weren’t enough of one kind to build even a patio planter wall, these bricks often end up in landfill. We’re grateful that Ibstock Bricks Ltd donated these bricks. They’re so beautiful and mixed-up they make a great multi-coloured plinth.


11 tons of aggregate to act as a capillary break beneath the hemp slab: The pyramid at Gizah how are ya?!


The plinth takes shape.


The drainage/vapour channel within the capillary break sub floor goes in.


The blinding bound with lime goes down on top of the stone sub floor.


Hemplite – softy and fluffy initially, hard dense and insulating within a few weeks.


Hemplite – even over a drive from Clones to Dublin it hardens enough to create this smooth surface when the trailer gate is opened.


Tamping it down: there’s so many ways. Marcus demonstrates the step-step method!


Weighting down the 300mm deep Hemplite floor after laying and tamping. Like traditional thatch weighting the material down (with plywood sheets and blocks and flags) helps bind it to itself better and increases its strength.


The slab certainly has no problem supporting a 16 stone man!


These are two Hemplite samples Marcus McCabe gave me made a few months ago sitting on the new Hemplite slab. You can see the samples are lighter in colour. They are very light, totally rigid and seem very strong. The building should test the key characteristics. The yellower sample has more fines (so appears more homogenous) and was made with partially retted hemp fibre (which therefore still retained some chlorophyll) giving it the yellowish colour.

Controversially Hempire Buidling Products Ltd use the hemp fibre and shiv (or ‘hurd’), i.e. the woody core, in their structural mix. It makes processing much cheaper and thefore suitable for downscaling. Other manufacturers go to huge effort and expense to capture the highest possible quality fibre.


To the left is a concrete block used as some basic formwork: to the right is the edge of the Hemplite floor. My figure can only go in 5mm a week after it’s cast. A few weeks later and it should be totally rigid.


The LECA (light expanded clay aggregate) beads get poured in. It’s like building with Aero bubbles!


The 200mm of loose coated LECA is levelled-off. However it’s too high. We need 100mm of LECA-limecrete above this flush to the top of the brick wall (we only have 75mm space available here). Unlike the Hemplite floor which the Hemplite walls will be bearing on, the LECA-limecrete floor is not designed to take a Hemp-Lime above it, therefore we will have to provide a load bearing wall for the wall’s full width – watch this space!



Thursday, July 22, 2010