Help Needed: A few questions about Polyester Resin

[lunchweek]

Hi,

I'm totally new with polyester resin and fiberglass. I'm trying to make my Pepakura Judge Dredd Helmet, but have a few questions about polyester resin.

1- The guy who sold me the polyester resin added some cobalt in it, which gives it a bright blue color. Since the resin in all the build pictures I've seen so far was clear, I was wondering that it'd be a problem.

2- I've made 2 test coats before coating my Dredd helmet, but it still feels tacky after 3 days, even though I stirred both the cobalted resin and the catalyst vigorously. What may cause the tackiness?

3- The test run still smells like hell. Is it normal? Will the smell eventually go?

Thank you so much in advance!

 

[Canobi]

Polyester resin is not that nice to work with (I had to ban the kids from the bottomed of the garden where my shed is as I'd made a polyester casting in it, it stank for four weeks :/


The resin might be tacky for two reasons, lack of exothermic reaction due to thin castings (heating the mould during the cure time will help with thin parts), and exposure to air while it cures (basically down to exotherm again as Thor outermost layer won't get warm enough to harden properly.

Not sure why the vendor added the cobolt, was it requested? If not, a drop extra of the catalyst might see you ok.

 

[lunchweek]

Thank you so much Canobi. I'll try with an extra drop of catalyser.

 

[Canobi]

If you still struggle after trying a bit extra catalyst, give this a try:

Polycraft FC-6620 Fast-Set Water Clear Polyurethane Liquid Plastic Casting Resin - mbfg.co.uk

Polycraft FC-6600 Slow-Set Water Clear Polyurethane Liquid Plastic Casting Resin - mbfg.co.uk


They need addition cure silicone, but the working times the same as polyester with the advantage of not stinking to high heaven and are a lot less toxic to handle.

 

[lunchweek]

Seems awesome, but since I'm from Turkey, it's extremely hard to find/import chemicals for me. I've found the polyester resin after a few months research

 

[Canobi]

Ah ok. Just go easy on the catalyst as too much can make a casting crack due to aggressive exothermic heat reaction.


For thin parts, or to get away with using a little less catalyst, warming the mould to 50c prior to pouring will help the cure process, and vastly reduce the risk of micro bubbles.

Allow the recommended cure time, then a spell in an oven @ 50c for 2-4 hours will take care of any tacky surfaces on exposed areas. Moulds can act as heat sinks and draw the warmth needed for the reaction, heating it up makes sure all areas are warm enough to cure properly :thumbsup


A lot of folks use a pressure pot compressed to about 50psi with the mould inside and leave it to cure in the pot. The pressure stops the bubbles from being able to form during the reaction, and it also forces the resin into any fine details, so high quality, delicate castings are achieved, but is an optional item.



Dont forget to post pics of your work

 

[lunchweek]

That's some precious information, thank you so much Canobi. And I'll be sure to post some pictures!

 

[Canobi]

no problem buddy, glad I could be of help

 

[tsenecal]

as to the smell, it will drop off after a week or so, and won't really be noticeable, but it never really leaves completely. I have a model tugboat with a polyester fiberglass hull that was cast in 1983, and if you stick your nose down deep in the hull, it still has a whiff of that odor to it.

 

[lunchweek]

I actually kinda like the smell, but I2m not sure it's still hazardous after it cures.

 

[Jsimon999]

I actually kinda like the smell, but I2m not sure it's still hazardous after it cures.

I've tried to work with the polyester resin a couple times and I never got it right. Combining the two parts I found nearly impossible to get accurate; my pieces never hardened correctly and always had a tacky feel. And the smell....wow. Took a day to get out of the house but it will eventually go away as the piece hardens.

I'm sure with practice and experience it can be used but I'm never using it again. I gave away the bottle of it I had. I like Easy Cast (2) part epoxy resin. It can also be bought in (1) gallon sizes and it's much more forgiving on mixing ratio and smell.

Not sure it will be appropriate for your application but hope that helps.


Jon

 

[lunchweek]

Thank you Jon. I've heard very good things about epoxy resin. I'll try to find it here in Turkey

 

[robn1]

Another vote for epoxy. I've been using Smooth-On's EpoxAmite for fiberglass and it's great stuff, and no smell. Epoxy is common in boat building and repair, so look for shops that offer boat supplies if you have trouble finding it.