We’ve recently re-focussed our efforts on clay plastering. Clay plaster works brilliantly when applied directly to straw, as it allows moisture to permeate back & forth, effectively acting as a moisture buffer. It’s a healthier option compared to cement or gypsum plaster and will add significant thermal mass to the building – we have 7 tonnes of it to put on walls!
Some straw buildings treat the clay plaster as airtightness layer, but this can be problematic, particularly if there are tricky junctions. We use the clay plaster purely as an internal finish, and airtightness is dealt with by a separate membrane, installed to outside face of straw panels. More details on that are in my previous post.
We have sourced our clay plasters from a Czech company Picas, as recommended by our Slovakian plasterer Roman. I met Roman at an Ecococon event in Lithuania in May last year (short video from the event) and it was great when he agreed to plaster our house. The first few days were spent fixing reed mats to exposed timber elements – this will provide a good key for clay plaster. We’ve started with plastering the straw external walls, where two base coats will be applied before the final finish coat. We found our little fans a bit inadequate, so borrowed the neighbour farmer’s big fan to help dry the plaster out – it’s been working a treat.
We’ve installed a couple of DIY moisture probes that will enable us to keep an eye on humidity levels in the straw panels on both north and south facades.
After the first week of plastering Roman has finally finished the first base coat on all straw walls – a bit of a milestone. On to the second coat tomorrow!