Note: To protect the privacy of our members, e-mail addresses have been removed from the archived messages. As a result, some links may be broken.

Find Lesson Plans on! GettyGames

Plaster, friend and foe


From: Marvin Bartel (marvinpb_at_TeacherArtExchange)
Date: Mon Aug 25 2003 - 07:01:42 PDT

These are a few points that may not have been covered in the recent
plaster discussion.

PROBLEM - plaster breaks our best work
I stopped allowing plaster in the student clay production room for
the last 15 years. Fortunately, there is nearby room for plaster
when life masks, etc. are being made. Too often plaster chips
contaminated the clay when it got reprocessed. Inevitably the chips
cause pop outs and breakage in subsequent work when it is fired.
Murphy's Law generally used these chips to ruin our best artwork.
Advanced students (and I) were refusing to use reprocessed clay. This
created an unreasonable backlog of old clay mush waiting to get

Instead of plaster bats banging around the shop, wet pieces are now
placed on cheap imported unglazed ceramic floor tile. These help dry
the bottoms until the top firms. I dry all work up-side-down as soon
as the top is firm enough to support it. The bottoms and top rims
are less apt to crack from uneven shrinkage. For this to work, the
tops must still be a bit moist when the piece is inverted. This is a
good time to finish the bottoms before drying.

Heavy canvas on the cracked wedging board keeps plaster out of the clay.

PROBLEM TWO - plaster stops up drains.
It hardens under water. Plastered pipes are costly to replaced.

Hands and tools are pre-washed in old plastic buckets or containers
from the cafeteria. Similar containers are used to mix plaster. We
spread the wash water out on the grass. The containers and residue
plaster are trashed.

I look at the form and estimate water in a bucket for about half
enough. I mix it and quickly dump it in. If it is half full, I
immediately make the same amount again and fill it. It it is above
half, I make a smaller batch to finish it. If it is below half, I
finish with a bigger batch. If you want a stronger top, use less
water in the top layer. Avoid warm water - it may set too fast. I
do not wash up between batches, but the second batch sets fast if a
residue of first batch plaster is part of it. If you are
inexperienced, wash up or change mixing containers between batches.
The layers do not delaminate if the the plaster is poured wet on wet.
option 1: Lay a loop of stainless wire under the second layer a
SuperBlock that will never fall apart.
option 2: Include a bit of portland cement with the plaster for much
stronger plaster. It is less absorbent.

Check this page (from a New Mexico supplier).

Marvin Bartel, Ed. D. clay artist and art educator