Invent Design Make

Finishing coat mixing and application

This time we used a big barrel-off-cut for the mixing (which was easier than a wheelbarrow) as the mixture is more liquid like. We found that adding some water to the earth, sand and borax then mixing as you would cement with a spade worked quite well to combine these ingredients roughly. You need to be careful of adding too much water at once, there is a fine turning point between too dry, just right and too wet it seemed to us.  You’ll get a feel for it when making test batches.

Then we added the hair and a little more water and got stuck in there with hands. It took a fair amount of mixing to get the hair evenly distributed and non clumpy. The first time round we tried things like food mixers, but they didn’t seem to help much, fun though, and the plaster did look like an interesting version of coffee cake mixture!

Again we left the plaster for a few hours to let it plasticize and gave another stir before use.

Like the other coats, the wall needs to be wetted down before adding new plaster to help it bond together. The undercoat will tend to suck in the moisture and so wetting will probably need repeating regularly. We were a little worried that a few patches of mould were still around so we also treated them with borax solution before plastering over them, which seems to have done the job.

Given you are likely to keep hosing the wall, we found it a good approach to start at the top so you don’t keep wetting the newly applied plaster. Again we got better at it towards the end, so start where it matters least if you can.

To apply we get a load of plaster on the hawk (we were just using squarish scraps of plywood for these) using the trowel. Then push the plaster from the hawk onto and up the wall with the trowel using mainly smooth long vertical strokes. Try and keep a wet edge and minimise the edges exposed when you need to take a break, taking special care to give them a good wetting when starting up again.

As mentioned in the equipment step we found late on, that a big trowel was much quicker and nice to use for large straight forward areas and smaller ones worked well for more fiddly, curvy bits.

It’s easy to get carried away, but you’ll need to stop every now and again to either polish or sponge what you’ve already done, it is much easier to do this way that to re-wet and re-work, though this is possible if you need to.

Polishing

We used small circular pieces of damp proof course to massage the clay – smoothing out the trowel marks and closing up the gaps between particles. This is best done when the plaster no longer has surface water showing and isn’t soft to touch, but is still workable. Hard to describe, ‘leathery’ some people call it, but it will be relatively easy to polish if you get the timing right. If it is too wet, you won’t get a shiny surface, but a sort of sandy one, if too dry you’ll know because you really need to put some elbow grease into it to get it to do anything at all! If it’s too dry, you can use a hand mister to try and get it back to the sweet polishing spot, or over a large area, use the hose mister.

One tricky thing is that the plaster will dry at different rates in different spots depending on thickness and the substrate, so judging the timing is tricky.

After the event we heard of using polishing ‘stones’, this might have been the easier and more effective, we don’t know.
As it was, this was hand-hurtingly tiring, so much so, we decided not all of the internal walls needed polishing and we switched to sponging for one of them…

Sponging

Again, easier to do if you time it right, though the window of opportunity is much larger with sponging. We used dampened washing up sponges to gently even out the trowel marks and smooth it over. This creates a rougher, sandy, rustic kind of look.

Then the final waiting game for that to dry before applying a finish. It takes much less time for this coat to dry as it’s so much thinner. Meanwhile we found we had a large amount of clearing up to do, mud, mud, mud!