It was a beautiful day in Philly today, so Kelly and I decided to play with some plaster and try making arches using gypsum mortar and split bricks. We had two goals today: (1) Test out two types of plaster to determine the correct ratio of powder to water for each and pour test cylinders (2) build two simple arches using each type of plaster.
Plaster "A" and "B"
architectural test tubes
Plaster Chemistry: precision mixing
test cylinders: marked with powder/water ratios
Yes Kelly, science experiments can be messy.
Our 8 plaster sample tubes.
After our tests, we determined that plaster "A" needed a 3:1 powder:water ratio in order to be effective as a true gypsum mortar. Plaster "B" needed a 3.5:1 ratio because it was a much finer powder. Next, we moved onto making our first tile arches.
True Catenary Curve using a hanging chain.
Cutting out our formwork.
Little by little, building the arch from both sides.
Removing the formwork...
The first arch worked!!!
The second arch ALMOST worked...
Even after we destroyed the arches, a few tiles remained in cantilever.
Look at that gypsum mortar work!