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Testing the second coat of plaster

This coat is the main shaping and straightening out coat. We still want plenty of clay to bind it all together and make it sticky, but we don’t want it to crack and shrink as much. So we have plenty of fibres again, and this time more sand, without it being too crumbly.

The results from the first round of testing might have given some useful clues as to possible ratios to try for the second coat. For comparison our mix was thus:

The sand could have been 2 buckets of the same sand, just we had two types to use up! We chopped the straw a lot smaller this time, and because we were measuring by volume, this effectively meant we had a lot more fibres in the mix.

for the second coat we did a nice big test patch on the wall itself so we could properly see how it adhered to the first coat  – though, better to do this in a non-prominent patch as it is hard (not impossible though) to join dry and wet plaster together: even when re-wetting lots, it’s tricky. Or it might be better just to chip this off and start again (but if you can do that easily once it is dry the second coat’s adhesion is seriously suspect). Make sure you wet the wall well and then apply slip, as you would for the second coat generally, for the test patch.

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