How much work time until fiberglass hardens?

I bought a bondo fiberglass repair kit from Walmart, and I want to reinforce the inside of my 2 mystery helmets to make them stronger. I've used a lot of bondo in the past and I know I only have a couple of minutes to work with it until it hardens. My question before I mix up the fiberglass resin and hardener is, how long do I have to work with it until it hardens?

Work very very fast. Try not to mix too much of it at once, too much of it at a time can dry quickly and you will be loosing materials.Mix small amounts at a time.

It depends on how strong you catalize it, the temperature of your environment, and how thick you apply it. I usualy add about 2 or 3% catalyst by volume. At 70-75 degrees f., you should have about 15 minutes of working time, before it starts to gel. If you get any on the outside of your bucket, clean it with a rag soaked in acetone, asap. It washes away quite easily, if you get it before it hardens.

i add about 8 drops per 1/2" of resin in a paper cup...so dont add alot....unless u can apply it fast....lol

Man oh man, why didn't someone warn we how messy this fiberglass stuff gets! :p I've only done about half of the inside of one helmet, before I was sticking to everything around. I went through a lot more of the resin than I thought I would, too. Live and learn. Well, I know a lot more for the second application and will take proper precautions. I'll also use less hardener, then called for on the package.

Are you also using a breathing mask? ''D O N 'T BREATHE THE STUFF''.

Wear some gloves too, it usually works well to use a disposable 1" bristle paint brush to smooth out the glass and resin to remove air bubbles once you apply it. Work in a well ventilated place, like a geradge with the door open. Have your pieces of glass cloth cut and ready to apply before you mix the resin, and, like METALLBOY said, wear a respirator ...... that stuff is a tad on the nasty side :lol

Ive ben werking wif it for 30 yeers, end it does not dun eneethings too mee. :D

lol...i make my surfboards with out a mask...its ok...than again i spraypaint in my bedroom, adn bondo in the living room....i cant smell a thing... :)

:lol

My neighbors won $1000 on Funniest home videos from tapeing me tear off all my clothes and roll around in the grass when I thought I had spiders all over me when I used to use glass without a mask, they wouldn't split it with me .... so I started to wear a mask :rolleyes

for real?

ohh yea, and i just bought a fiberglass kit, and i heard about how dangerous this stuff is to breath. so i thought, how long does it takes before it's safe to put on the helmet, and not getting the "gas" into the lungs hehe?

even though this thread is about four years dead, you do ask a good question. i'd recommend letting the fiberglass off-gas for at least a week in a well ventilated place that you aren't going to be spending a lot of time around; like in the garage near an open window. or near an open window in a spare room with a fan blowing outside and the door closed.

yeah, i know this is an old thread but i would like to do this very thing. reinforce my helmet by fiberglassing the inside. I've never worked with it before and am trying to get as much info as i can. i was wondering if it was necessary to use the cloth if i was just reinforcing or can I go with straight resin application only?

I would go with a few layers of cloth as the resin isn't as strong on its own

what's the best way to prep the cloth? lay it in then apply the resin or coat in with the resin before laying it in?

when i'm working with fiberglass i like to have a piece of cardboard handy, i "wet" the cardboard a bit with resin, lay the piece of cloth down on it, then paint more resin on the cloth with a foam brush, flip the cloth over and spread resin on the other side as well, then finally lay it into place. be sure to be wearing disposable latex gloves while you're doing this, just get a box of 100, you're probably going to go through 2-3 pairs, maybe more depending on the size of your project.

Persoinally, I 'paint' a layer of resin on the area where you'll be laying your fiberglass on the part, lay down the dry cloth on that area, then evenly 'paint' on some more resin over the cloth. It's at this time that you can roll/stab out any air bubbles in your work.

Thanks for the tips guys. I just saw a tutorial where the person coated the inside with a spray adhesive, laid down his cloth, then applied the resin. seems like the easiest way to tackle this. Any drawbacks to this approach?

Right of the bat, that seems like a pretty workable approach. My only concern is that you have two different binding agents: fiberglass resin vs. glue/contact cement. Glue/contact cement might dry out and age over time, weakening the bond between your material and the fiberglass reinforcement.

My approach is to rough up the material surface with some 120 grit sandpaper so that the fiberglass reinforcement has some more grooves, pits, and surface area to attach itself to. A smooth surface (like cast resin parts) won't 'grab' onto the fiberglass unless the surface has been roughed up somehow. Before reinforcing my MOW resin gauntlets with fiberglass on the insides, I used a coarse drywall sanding sponge to rough up the inside surface. It's never peeled away. Yet I was able to peel off big chunks of excess fiberglass resin that dripped on the smooth non-sanded outsides with my fingernail.

Yeah, Necronaut, I've been checking out your thread. cool stuff.

I would definetly rough it up first. And I would think that you would just need enough spray adhesive to position the cloth. Like I said before, I've never worked with fiberglass before but I would assume that the resin would soak through to the other side but I guess I really don't know that.

Everything I learned about laying fiberglass down I got from this guy's youtube channel: GasserGlass - YouTube
Most of his videos focus on making molds of car parts, but the basic principles and techniques still apply. Highly recommended!