Bathroom

People in Australia don’t seem to understand the importance of managing humidity. It irks me when people fail to use exhaust fans when cooking or even showering.

The new fan — Panasonic FV-24JR3 — turns on with a motion sensor and runs on for 15 minutes after use. It also features constant ventilation: it runs all the time at a low speed, very quietly, to ensure full drying and a base level of fresh air in the building.

Clay plaster
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Clay plaster is one of the oldest building materials and yet it seems like advanced nanotechnology. Sheets of aluminium oxides alternate with sheets of silicon oxides. It has an incredible ability to absorb and release water vapour: it is hygroscopic. That means it regulates humidity levels. Useful in a bathroom.

Clay also adds thermal mass to buffer temperature. And makes the room feel cosy.

Wall preparation
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The existing plywood walls are not a good substrate for plaster. A “key” is needed for the plaster to hold on to. I applied two kinds of keys.

For a small-scale key, I mixed wheat paste with coarse sharp sand and painted that onto the walls. Wheat paste is a glue made by cooking wheat flour with water.

For a larger-scale key, I fastened mesh onto the walls with staples and nails. These were various old bits of wire mesh I had lying around, as well as some fibreglass plastering mesh.

Walls with a key for clay plaster: sanded primer and mesh

Basecoat
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For the base coat I used clay subsoil dug from under the house. A soil composition jar test confirmed it was clay and sand with little silt or organic matter.

To remove stones I passed it though a home-made sieve of 5mm mesh.

Finally I added plenty of coarse sharp sand, and some chopped coconut fibre, and mixed with a paddle mixer.

I laid it on about 10-15mm thick and compressed it firmly.

Topcoat
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For the top coat I used bagged “builder’s clay” (kaolin) as this is very fine textured and a lighter colour. One bag was enough for the whole bathroom. I mixed it with an equal volume of fine white silica sand.

The top coat was applied a bit thinner than the base coat. Clay plaster becomes sticky when thoroughly wetted. So spraying the surface beforehand allows the top coat to bind to the base coat. (Not shown in the photo below.) It should also be applied with force.

Top coat clay plaster being applied (note the base coat should be wetted first)

I finished it with a wet sponge. After it had dried I went over the surface with a dry cloth to remove loose sand particles.

Floor
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I started by laying down moisture-resistant fibre cement board (9mm Villaboard). This proved to be a bit of a geometric puzzle but I got there in the end.

Over that went a cement-lime-sand mix reinforced with fibreglass mesh. (After which the new toilet and vanity could be installed.)

Finally I painted the floor with hard wearing enamel paint (from the trusty mis-tint discount shelf at Bunnings).

Door
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I picked up a “cedar door” for free. Actually it was a normal door with cedar boards on one side and melamine on the other. The only catch was that it had been painted. Sanding off the flat surfaces was easy enough, but the grooves not so much. I used a combination of a router and hand sanding to get it done.