Getting plastered

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Offline DoctorBeaver

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Getting plastered
« on: 29/03/2007 09:13:15 »
We've got the builders in and they're doing plastering. What's plaster made from & why does it go sticky then hard when mixed with water?
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Offline daveshorts

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Getting plastered
« Reply #1 on: 29/03/2007 09:52:42 »
Plaster is based on Gypsum CaSO4, it is found naturally with Water in the crystal structure. CaSO4.2H2O  - there are 2 water molecules in the structure for every CaSO4 this is then cooked in a furnace which drives off the water to produce CaSO4.0.5H2O which is the powder.
You then add water which allows it to hydrate again to CaSO4.2H2O this has long thin crystals which grow, and cross each other and interlink with each other making it solid.

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Offline DoctorBeaver

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Getting plastered
« Reply #2 on: 29/03/2007 13:30:03 »
Thank you, Dave. As always, your answer was erudite & comprehensive.
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