Plaster batts are quick and easy to make and can be used for lots of things
This was used for our project using casting slips to make a slab vase in issue 22
You will need:
Buckets for mixing
Scales for weighing plaster
Clay – old plaster clay (if you have some) is fine as long as there are no large lumps of plaster in it
Plastic sheet – Rolling pin, roller guides (min 10m thick)
A3 sheet of card or paper
You will need a large block of clay for this project because it will be rolled thicker than usual and to a large size.
Working on a sheet of plastic, reduce the bulk of the block of clay.
Beat the clay with the side of your rolling pin. Work in measured, even strokes from one side of the clay to the other, to avoid making deep grooves in the surface.
Roll out the slab between your roller guides to ensure an even thickness of clay.
When half rolled and still much thicker than the roller guides, square off the corners by rolling the pin sideways, freehand.
Now lift and turn the slab as normal and roll again until level with the roller guides.
Test your A3 template over the slab regularly to ensure it is the correct size. If you find you have wildly overestimated the amount required simply cut it down to a more approximate size as you roll and turn.
Once fully rolled, smooth over the surface of the slab with a rib to compact the clay.
Place the template back on the slab and cut it to size using your batten as an extra guide for cutting the edges straight.
Lift the slab on the plastic sheet and carefully turn it over onto a non-absorbent board.
Peel off the plastic sheet then smooth over the surface with a rib again.
Roll another 10mm thick slab of clay. It must be longer than the longest side of the slab by approximately 6cm.
Cut the slab into four strips, 5-6cm deep.
Use the strips to build a wall around the slab – 10mm from the edge.
Reinforce the walls with coils of soft clay to prevent plaster spillage later.
If you place your roller guide on the inside of the wall and hold it there firmly as you reinforce the outside, it will help keep the wall straight.
Overlap the wall strips at each end and smooth the clay together to prevent the wall bursting open.
Check the wall is straight when you come to the last section by placing the batten on the outside.
Complete reinforcing all walls.
TIP: if you are worried about the sturdiness of clay walls, masking tape can add surprising extra strength. Simply wind the tape around the wall 2 or 3 times – it will easily stick to itself after the second wind.
Measure 6 pints of water into a clean bucket.
Weigh 9lb of plaster.
Add the plaster to the water a handful at a time but taking care not to create too much dust.
Stir the plaster with your hand (or a mixing tool if allergic) to remove any lumps.
Periodically scoop off any bubbles from the plaster mixture into a newspaper-lined bowl.
Keep stirring until the mixture begins to thicken.
Once the plaster begins to thicken you must work quickly.
Pour the mixture into the frame, filling it to just short of the top of the wall.
Once all the plaster is in the frame, wiggle the surface with your hand to bring any trapped air bubbles to the surface.
Leave the plaster to set. It will go through a chemical process which causes it to heat up, once this is over you can then work on the batt further.
While you’re waiting, clean out your plaster bucket with newspaper and tidy up the work area to avoid any possible plaster contamination.
Before removing the clay walls, shave off any irregularities on the surface of the plaster with a surform so that it will be level and sit flat when turned over.
Now remove the clay walls. Reserve the clay for future use in a dedicated PLASTER CLAY bag. Label it clearly not to confuse it with other clay.
Surform the edges of the batt to remove any sharp areas – include the corners.
Dispose of the plaster shavings carefully.
Your batt should now have clean rounded edges ready to be turned over.
Once turned over, surform the upper edges as you did on the underside.
DO NOT dig into the clay to remove the slab – lift it at one corner with a wodge of soft clay. From there it is easy to lift out and can be stored with the rest of the clay in the plaster clay bag.
Wipe over the surface of the batt with a clean damp cloth to remove all traces of the clay.
Your finished batt must be placed somewhere warm to dry out thoroughly before use. Try the airing cupboard or on top of the kiln – just make sure it is elevated if placed on the kiln.
See more of our ‘How to’ projects here