Placing hempcrete - The Hempcrete Topic: Designing and Building with Hemp-lime - page 371

Unsurprisingly, it is common for walls with better exposure to prevailing winds to dry
more quickly, and for the tops of walls to be drier, as the water will naturally run down-
wards within the hempcrete to a certain extent. Walls that have had recent driven rain may
show an inaccurate reading on, or close to, the surface. However, even quite prolonged
driven rain shouldn't penetrate far under the surface, and should evaporate quickly in dry
weather, so sub-surface readings should still be accurate.
In the information provided to the authors on the use of their Tradical ® HB binder, 1 Lime
Technology suggest that the 'dry' crust needed before plasters or renders are applied is
represented by achieving readings of 23 per cent WME or lower on the surface and up to
35-40mm below the surface, and we have found this to be a useful rule of thumb.
Finally, it is common practice, where both sides of a hempcrete wall are to have a wet fin-
ish applied, and if the contractor is not happy that the wall is sufficiently dried, to finish
one side after 6-8 weeks and leave the other side 'open' for as long as possible. This can
be a compromise in situations where there is pressure on the contractor to apply the render
finish so that scaffolding can be removed. The render can be applied, and the inside face
left open as long as necessary before plastering internally.
Conversely, on a single-storey build, it might make sense to apply the internal finishes and
to start using (and heating) the building, then come back several weeks or even months
later to apply the renders, as long as the bare hempcrete walls were not left exposed to
extremes of weather (though a bit of rain won't matter). As a general principle, leaving
hempcrete for as long as possible to dry out before finishes are applied can only be a good
thing.