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Things to know about earthen plaster before you begin

Lets just run through some common questions to do with clay plaster, worth asking yourself before starting any project:

What are the main reasons for using clay?

Are alternatives worth considering (alternatives are always worth considering!)? This GreenSpec page has an excellent summary of the properties, suitable situations and environmental considerations for all the major plastering options, though it may slightly undersell gypsum plaster. If sourced from “flue-gas desulphurisation” (FGD) of power station emissions, this is arguably made from a waste product that performs well and has little wrong with it – it certainly doesn’t have the ‘pure untarnished by industrial processes’ feel to it that clay can have (if you dig it yourself), but is worth considering (possibly used as a mix with clay for final coats).

Will you buy-in the materials or dig your own? If buying the plaster mixes, this can become expensive especially if you have a large area to cover, but it will drastically reduce the time and labour involved, and will probably require less testing. One the flipside, you may not learn as much, and will also lose out on some of the fun of taking a raw material all the way through to a finished product.

What time of year will you be plastering? The plaster will take a good while to dry – several weeks for the thicker base coats. In temperate climate such as the UK, attempting this is winter would be a lot like madness, drying times would be very long so mould would be a real problem, and you would be in major ‘fail from frost’ territory.

Have you got plenty of energy and enthusiastic friends to support and help out? This is a serious consideration if you are going the whole hog and testing, harvesting, mixing and applying the plaster yourself – but depends on the scale of the area to be plastered and if you are willing to pay for labour.

Are you up for learning as you go or will you need prior training/ experience to feel confident enough to get started? The low budget option for training would be to find volunteer opportunities on other people’s projects to gain experience, or you could invest in training (see resources).
Have you got the time? Did we mention it takes a long time already? As a rough indication we started soil testing at the end of April and are painting on finishes mid-September. Ok so we haven’t been JUST doing the plastering all the time, there have been many days off and work on other things, but a lot of that has happened whilst waiting for coats of plaster to dry. Having working parties takes a fair amount of organising and preparation, but you can get large areas done pretty quickly this way (and spread the fun and skills around a bit). We had a couple of these, otherwise it was mainly one or two of us plastering.

A common approach is to use local earth, if appropriate for the base coats, which are bulky and won’t show on the final finish and then buy in the final coat mix, with there being lots of colour and effect options and higher chance of it looking like the text book pictures!

We don’t want to put anyone off clay, many of its weaknesses; like the fact you must keep rain off it, are also its strengths; it is hygroscopic and provides a very pleasant, healthy environment.