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Casting Resin issue? Answered

I'm trying to cast some resin claws for a halloween/convention costume I'm trying to make ( it isn't a Wolverine one .. more a VERY twisted, evil, and blood thirsty Mad Hatter character ) and running into a bit of trouble. I'm following the 5 drops of hardener per 1 oz of resin that is stated on the resin can's instructions. It also says it's supposed to set hard enough to support objects at 40 minutes. I mixed a 2oz batch of resin ( 10 drops of hardener ) and poured it into a rubber latex lined plaster mold that I had sprayed with mold release. I put a bolt down partly into the resin so I can later attach a wire to it and left it alone for about an hour to an hour and a half. I came back to check on it and the bolt was still able to be moved/removed with NO resistance. I figured the mix was bad and threw it out, but noticed it was the consistancy of slime. Did I mess it up and not wait long enough, or did I not add enough hardener or what ? Any suggestions would be great!


Sounds like you are using Polyester resin which I am not an expert on. I do know it is the cheapest (or used to be ) burt also very toxic. Urethane is easier to use and should cost less too. www.rtvmoldmaking.com

 Many people will have problems with using resins!
MOST IMPORTANT.......Read and perform the instructions to a "T"!!!
 If you use more hardner, the casting will become very brittle, if you dont use enough the casting will be flexible to an extent.

Use a clean mixing cup when mixing, AND STIR VERY WELL!!  When you are sure you mixed the 2 parts throughly mix them again and bet sure to scrape the sides and bottom of the mixing container!!!!

    If you dont mix throughly you will have a casting that is tacky, wont cure properly, etc.

     Just read the instructions, also you won't need a release for a silicon mold.    Good LUCK!!!!!! 

Are you using polyester resin, Urethane ? Does it have to be crystal clear. If not use milled fiber inside the resin to stiffen it up or saw dust. Something composite. Also mix well and if its not kicking after 30 min use a heat gun 6 - 8 inches away from it but dont hold in 1 spot too long and only do it in 30 second intervals. I have used 3 year old resin before with great results. I have been in Fiberglass and molding for 11 years ( for street cred).

Your mix could be off.

There might not have been enough heat created to 'kick off' the resin.

You might have an old batch.

But most likely, something in the mold, mold release, bolt, mixing cup or mixing spoon or even something you touched contaminated the resin and prevented it from setting up. 

I tried it again today, and increased the amount of hardener I put in there. 30 minutes later, I can physically shake the mold and it isn't moving. I'm gonna let it set for a few more hours just to ensure it's cured. I'm betting on the "Not enough heat created" deal causing the issue. Thank you !


Answer 8 years ago

Yep, it was the amount of hardener per oz of resin that was the issue .. both claws I've made so far are rather rubbery ( one was just made today) but the one from yesterday is much harder than it was when I pulled it from the mold. However my plaster mold cracked today, so I'm going to form a latex rubber one from the first claw ... here's hoping it works easier.