Hempcrete
dajn
| Posted in Green Building Techniques on
When building the exterior walls of a house with hempcrete, do you have to worry about cold joints if you don’t finish the whole wall in one day? Can it be done with a 1 or 2-man operation where it takes several days or weeks to complete the exterior walls, or would this result in many “cold joints”, in which case it would be better to have a larger crew that could complete the exterior shell in less time with less “cold joints”? If using the exterior hempcrete walls as your primary air seal, would building the walls slowly over time leave a bunch of cold joints that would negate its ability as an effective air seal?
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Replies
What is the binder being used? What people describe as "Hempcrete" remains a bit variable.
In certain other masonry applications, Portland cement (which cures and dries rapidly) can form cold joints easily and crack, while lime (which is less than perfectly solid over long periods of time & varying moisture levels, and cures & dries very slowly) tends to be self-healing.
I think your exactly right in asking what binder will be used; I haven't determined that yet, and choosing the proper one, and maybe experimenting will give the optimal binder for a relatively slow build up of the walls. Some binders have portland cement included (a small amount) to give the hempcrete a quick initial set so that the forms can be removed and moved up the wall for the next pour. Therefore, if the portland cement amount is relatively small and the lime portion is high, maybe this allows the wall to be completed in more than one day with no cold joints, because the mostly lime binder takes days or weeks to dry appreciably. Everything I've seen shows crews working over a period of days + not necessarily completing a wall in one day. I'm guessing that with a lime plaster finish coat, hempcrete would provide an excellent air seal that is moisture permeable.