Culburra Hemp House: Hemp Wall Cracks and Problems

We had a long weekend ahead of us and so started with the most time consuming and difficult part, working in the section above the windows and below the roof. The section we did above the windows did not work as well as hoped. On the outside it was OK, but on the inside where the timber we had added to support the hemp was thicker, we had not left a large enough section to be able to fit our fingers in to tamp the hemp down and accordingly there was insufficient hemp coverage in these sections. We will patch them and hope that the render covers it all evenly.


Insufficient hemp coverage

A patched up section

My second issue was that as the walls have dried they have pulled away from the timber frame at the doors. I believe that this has been exacerbated by the large number of studs next to some of the doors, up to four studs together. The high walls and large openings for the sliding doors required additional support, hence the high number of studs. I am worried that these sections where the hemp has not been able to key into the other side may crack off. I do not know if such concerns are unwarranted as these edges are bound to the rest of the wall which is keys in to each side. Interestingly at the windows where the hemp is bound into the rest of the wall at the top and bottom the same sort of pulling away has not occurred.

The worst of the pulling away sections

My third problem is a number of cracks, a number of horizontal cracks have developed mostly where two rises join together. There has sometimes been a few weeks between when rises were done, hence the older sections were much dryer. Vertical cracks have also developed on each end of the back pavilion on the shorter walls just around the corner from the long 9.6m back wall. There is one crack in almost an identical position on each of the shorter walls, but no vertical cracks in the long 9.6m wall. Traditionally in a brick wall an expansion joint would be put in a long wall to avoid cracking, but here the cracks have appeared in the shorter walls.

Horizontal crack between layers

Another horizontal crack between two layers of different dryness

Vertical crack

To cope with the pulling away at the door frames I improvised a U-shaped metal bracket out of some left over fascia brackets. The metal, being much thinner than timber restraints, was spaced to ensure that I was still able to tamp all around the bracket. Whether this will work will only be seen once the walls dry out.

Metal bracket placed where there are four studs in a row

Metal bracket inside form work, with enough space left to tamp around it

On the positive side the plumbing rough in had been completed - on the first day my plumber got back from holidays (many thanks). The kitchen wall certainly had a lot of pipes and conduit through it - hot and cold water, gas and electricity.

Kitchen wall with lots of pipes

Holes made in form work for pipe penetrations

Predicted poor weather over the long weekend did not arrive and we did four days of hemp walling, with Tony once again helping us on the last two days. A third person made the hemp walling more than 50% faster, particularly on the low long easy runs where we quickly went through a lot of mixes. With all this effort we have now started all the walls except a few short ones beside the front door and between the glass sliding doors. To be able to do this we had to relocate two and a half of binder that were too close to the wall in the front pavilion to allow access. Almost one pallet was moved to and stacked up in the room we mix in and the other pallet was stacked extra high on top of the remaining two pallets in the front room. Storage of materials under cover of the roof, while allowing access to the walls has been an issue, solved with the hemp by using up half a bag until it was light enough for two people to lift up onto the other bags, therefore allowing us to clear the floor area quicker than if we had just used full bags.