Clear-Cast Resin problem

I'm currently having a few problems with creating a prop-part in clear-cast resin. All the test casts I have done have ended up with tackiness problems.

I'm presuming this is due to the ratio of resin to catalyst. Is this an exact science? Was I wrong to presume that the more catalyst added, the faster the cure-time (as I've found in many other resins)?

Anyone have experience with clear-cast resin that could give me any tips?

Urethane or Polyester?

For Polyester, you can increase the catalyst amount a little and it will help (but will also shorten the pot life) but I still have found that it remains tacky for several weeks... Increasing the catalyst in small parts is almost necessary as they don't create enough of their own heat to get a good reaction going... The only real solution I have found is to post cure it in an oven (I picked up a toaster over for $14.99 that works great) after the 24 hour cure or whatever cure time, drop the piece still in the mold, in the oven for 2-4 hours at 125° and then remove the piece from the mold and and put it back in the over for another 4 hours at 150°... Remove and let cool to room temperature before too much handling as it will be soft from the heat but should not be tacky any longer...

For Urethane it will generally lose the tacky surface in about 48-72 hours at room temperature, but again you can post cure it in an over at 125° - 150° for 2-4 hours after the 24 normal cure time... And again let it cool before handling as it will be soft...

I have been doing a lot of playing around with several brands of clear resin in the last few weeks and this is what I have come up with...

BTW: Urethane is a pleasure to work with compaired to polyester, and Smooth On brand is the best I have used so far (after several weeks of trying a lower cost alternative) costly for sure at that $150/gallon but so far the results were the best...

Are you using that Castin' Craft stuff?

If so, you'll never get a proper cure on it.

Believe it or not, this product doesn't actually state anywhere whether it is Urethane or Polyester, on its packaging or its website

It is called Trylon, and is a UK product. Thanks for the tips.

Urethane will generally be a 1:1 (or close) mix ratio of part A & B

Polyester will have a small bottle of catalyst (Methyl Ethyl Ketone Peroxide)

There are also acrylic ones with a 1:1 ratio (fake water in floral vases) I have had no luck getting acrylic to set up very well, and it starts to yellow in short time...

Trylon is Polyester resin - you mix approx 20ml of an organic peroxide hardener to a litre of resin.

exoray had some excellent tips - heating the resin parts post-cure should remove the tackiness, that's probably the best way!

Adding more hardener may actually increase the tackiness - the tack is caused by exposure to air. As the resin hardens & shrinks it can pull-away from the mould and you can get a horrible surface ripple effect that will remain tacky for what seems like a millennium.

I mix in 2% wax solution to the resin; this eliminates the surface tackiness with negligible effect. If you mix in too much wax solution the resin become slightly misty – less translucent.

BTW those are Fahrenheit temps in my post for our overseas friends...

Originally posted by blufive@Jan 30 2006, 05:13 PM
Are you using that Castin' Craft stuff?

If so, you'll never get a proper cure on it.

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I must have purchased a good batch of it, the humidity was just right, or just got lucky. Mine cured in 24 hours and was ready for the sander. After that, a liberal coat of future floor polish and it was done.

It may also depend on the thickness of the final product. My task was to submerse the origami unicorn in it so I had to poor and cure three layers in sequence. Each layer required less amounts of catalyst. I don't know why but that is what the instructions suggested. It worked.