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Question: Does resin shrink over time?
Hi Robert.
When you cast from a master, the moulding is always a little smaller than the master as resin shrinks during curing, so usually the master that fit perfectly will result in a resin copy that won't. Then, the temperature of the environment when you pour the casting has an effect on the cure time and with that a variable shrink rate. The cooler the temperature of the pour the less additional shrink.
Then the mix of the 2 resin components will also effect the curing rate, and the shrinkage rate as does the thickness of the part. The resin bonding creates heat during curing and this can effect shrinkage.
If the casting is removed from the mould too early, it too will contract of its own accord depending on air temperature, humidity, etc, the moulding now come in contact with.
That is all before the part is sold....
Once cured and removed, the casting has not really fully cured. This takes some additional time and is often the cause of warpage of parts and further shrinkage.
Then if there are excessive proportions of poly oils in the resin, these will weep over time and as they are released, the resin will contract further.
More modern formula does not have as big a problem as older ones, due to more understanding and better quality components, but if your piece is old, it will likely suffer most of the issues above.