As an experienced team lead, and an award winning hempcrete builder, I'll be the first to tell you that the benefits of using hempcrete in construction are vast.. However, without proper training, even a great thing like hempcrete can turn into a nightmare.
The wall on the right is how a hempcrete wall should look after its poured, It's a monolithic wall, meaning the hempcrete is wrapped around the structure. In this example there is 1" overlap on the inside of a post and beam frame.
In this type of hempcrete construction, its important to reinforce the 'crete with coated rebar, and use coated nelson studs to grip the material to the posts and the beams. These mixes were cost effective, not too dry, nor too wet, they were consistent, and there was virtually no "balling" of material.
The example below, shows a single timber framed wall. The builder decided to put the overlap on the outside of the wall. (it can be overlapped on either/ or both sides)
There were some major issues with this project:
-The horizontal form supports travel straight through the wall and into the living space. This is no longer a monolithic structure and will allow for thermal bridging into the home.
-Nelson studs were absent. This decision is questionable on a (single) timber frame that's been overlapped on one side. The absence of nelson studs may turn out be ok for the lifespan of the house, but a box of nails is money well spent for added resiliency in the event of a major earthquake.
-The mix that was used in this project was too dry in many spots which caused issues throughout. (light patches) The formula used was unnecessarily expensive, (Almost 30% higher). On top of that, each mix had between 10-20% wastage due to "balling".
-The horizontal form supports were difficult to pack around, voids under the supports allowed space for birds to make nests before plaster could be applied,
Before the inspector would sign off on this project, all the critters needed an eviction notice and all the dry 'crete had to be picked out and replaced. This resulted in an unexpected cost of repair, and delays in the build schedule.
Because of the versatile properties of hempcrete, most of these issues were correctable and the house did pass inspection. However, time and money could have been saved if an experienced consultant was involved from the start.
Hemprete is an amazing building material. However, for hempcrete to reach its potential, and for Mother Earth/ humanity to reap the rewards, we need success stories and competence at the helm.