Every cast passes through three phases. Knowing which one you are in tells you what you are still allowed to do.
The three phases
- Working time
- From the moment powder meets water until the mix stops flowing freely. Everything you intend to do — mixing, colouring, pouring, tapping out bubbles — happens inside this window. It is shorter than beginners expect, which is why preparation matters.
- Setting
- The mix stiffens and stops moving. The piece is taking its final shape and surface. Touching it now leaves a mark that will still be there tomorrow. Leave it level and leave it alone.
- Demoulding
- The point at which the piece is solid enough to leave the mould without distorting. Coming out too early is the most common cause of broken edges and warped bases.
How to prepare for a working window you cannot extend
Once mixing starts, the clock is running and nothing you do adds time to it. So the work happens before.
Have the mould in position, the container within reach, the spatula clean and the pigment already measured. If you are colouring, decide the colour before you mix, not while the material is going off in front of you.
Mix what you can pour. Two smaller pours you can control beat one large mix that stiffens before it reaches the mould.
Demoulding without damage
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Wait longer than feels necessary
The cost of waiting is nothing. The cost of demoulding early is the piece.
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Release the edges first
Peel the silicone away from the rim all the way round before you try to lift anything. The rim is the thinnest, most fragile part of most pieces.
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Invert, do not pull
Turn the mould over and let the piece come out under its own weight into your open hand. Pulling on an object still gaining strength is how you find its weakest section.
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Let it finish
A freshly demoulded piece is not a finished piece. Leave it somewhere level and unhurried before you sand, seal or load it.
