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Introduction to the clay plastering resource

For straw bale construction, clay plaster is a fairly common choice for the internal walls, but if you modify the technique appropriately, it can also be used on other wall types: insulating aerated blocks, wood boards, reed matting^[1]. These pages are based around our experiences of plastering the two strawbale walls of the FE workshop, both inside and out, with local clay (check out this post for our straw back-story), but should be worth a look for people considering plastering other wall types. There are lots of useful clay plastering books, blogs, and forum information out there, and many many ways to go about this, none of them necessarily right or wrong. We’re sharing our attempted meld of the most useful advice we found, and our own mistakes and successes while learning on the job.

The ‘system’ we used was: ‘slip coat’ – first coat – dry – re-wet and slip – second coat – dry – re-wet – third coat – polish/sponge – dry – vacuum brush – apply finishes (wall glaze inside/lime wash out). If that didn’t make much sense, keep with it, read on and all will become clear…

Some people don’t bother with a slip coat and just wet the wall, some people do an ‘all purpose’ first coat that binds to, and levels the walls, and follow it up with a finish coat. It will very much depend on what the surface is like that you’re plastering onto (known as ‘the grounds’) and the techniques you use, and the kind of affect your trying to create with the plaster.

1. ^[1]Stone, concrete and clinker do not provide good grounds for clay plaster, because they are so hard and dense – the clay has difficulty keying into the surface. It is possible if mechanical fixings, such as a wire mesh or similar is used to provide a key. ↩