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Molding is Not My Forte Answered

I am currently working on a future Instructable that involves a lot of molding. Hence, I've discovered that my molding abilities are not up to par. It has been almost twenty-four hours since I poured the clear casting resin and it is still tacky on the top. Is this normal, or did something go horribly, horribly wrong?



9 years ago

OOoOOoOOOooOOOoo Clear resin! Me like..

I'm, uh, I'm going to back away now. Real slow like, no sudden movements...

He got hold of one of those double strength cappuccino shots again, I bet LOL

What did you use to make the mold with? 'Cause I've been looking for something to use to make a mold.

It is called InstaMold, and I bought it at a craft store in Tacoma. I think it was called Michael's.

yeah I know of Michael's, we have one right across the parking lot from the A.C.Moore's craft store LOL

Thanks, I'll have to look for it sometime... We used to have a Michael's near here but not anymore :(

I don't really like driving across the bridge just to go to a craft store. At least there's an Ace Hardware and Home Depot on our side.

I bet, it must be kind of a hassle to drive over there. Not to mention if you don't like bridges it wouldn't exactly be much fun... The Ace Hardware around here closed down not too long ago :( Lots of stores have been, but none have really recently.


9 years ago

What kind of clear resin? Polyester "Clear casting resin" (catalyzed with drops per ounce of catalyst) can be heated gently to accelerate a cure (or fix a cure that'd didn't quite go, sometimes.) Epoxies (closer to 1:1 resin/hardnder) tend to be fussier; if they weren't mixed right they'll never harden. Fiberglass resins tend to remain tacky on the surface for purposes of putting on the next layer; you want gel coat or finishing wax on the last layer (or something like that.) I'd put it by the heater vent for another 24 hours and see if that helps...

It's the polyester catalyzed by drops per ounce of catalyst. I put it next to a heater and it seems to be hardening, I guess it is just too cold in the garage. Thanks!

I just did some clear polyester resin casting the other day. If I remember correctly. most polyester resins need to be above 70 degrees to properly cure. To get rid of the tackiness, you can sometimes do a post cure in an oven at a slightly elevated temperature- I did mine at 170 degrees for 90 minutes.

SInce the high was in the 50's in Gig Harbor, I'll agree temp is the problem. With a lot of resins there is an exponential increase in cure time with decreasing temp.

Yep, that is the problem. I doubt that it will reach 70 degrees again until mid-summer. The top of the resin seemed hard, so I took it out of the mold. Unfortunately, the half that was in the mold is still tacky, so the resin deformed. The heat lamp doesn't appear to be working. Honus- will placing the resin in the oven stink up the house or ruin the oven? That seems to be the only solution...


Does it still smell? If so, it might stink up your oven and/or your house. You could use a small toaster oven outdoors, but getting the temp right would probably require a thermostat. You definitely don't want the oven over 200 degrees Fahrenheit.

It doesn't stink anymore, but the resin is still tacky. I do have an old toaster oven though.

How about a cardboard box and an incandescent light bulb, use due diligence to avoid fire.

That looks like a really thick cast (20mm maybe?) Not sure if that will cure on its own without some help. It's an exothermic reaction, so heat will cure it eventually in a warm place. I'm not sure of the chemical properties of polyester resin, so it's best guess as to what effect putting it in the oven will have. You can cast the next one in thinner layers, pouring one in, mix another batch, pour that in. As long as the previous layer hasn't cured completely, the layers will stay together. Could make your next mould out of jelly to save some money. What are you making, out of interest?

I think the problem is thickness. The mold is still tacky, whereas the excess resin left in the mixing bowl hardened into a half inch thick puck. I'll try your method tonight and see if it helps. This will be the casing for a firing mechanism of a compound bow turned Airsoft bow.


9 years ago

Just going with what westfw said really. If you mixing of ratios was a bit off and it's still tacky, then put the mould somewhere warm like an airing cupboard or outside in the sun (which there might not be alot of). It could take a couple more days than you thought before it fully cures, but it's easier to just wait a few days more than have to start over again. Now that you know it doesn't cure in the guideline time, put more catalyst in the next time. First time I did casting and moulding, the resin I used was very old and the catalyst had gone all funky but I didn't know any better. Bought new catalyst and it worked perfectly.

soldering isnt my forte....