Fibreglassing

[Karl]

I've just mixed up a cup of Fibreglass Resin & Hardener 4:1 , (50ml hardner , 200ml resin) , and about 15mins into applying it to the Fibreglass Cloth , it started to steam , a few moments later , the cup was to hot to touch , and the mixture burnt through the plasic container! Any help ?
-Karl

 

[wyldbill]

It's curing too fast. This can happen when you have large volumes of epoxy. Epoxy generates heat as it cures and that heat accelerates the curing producing more heat. If you're going to use large volumes, mix them in a container with a large surface area (like a pie tin). This allows the heat to dissipate better and helps prevent the phenomonon you've just seen. You can also keep the mix in ice to slow the cure, though viscosity may be higher. Also, is your mix correct? Some epoxies' mixes are determined by weight, not volume, as the resin and hardener have different densities. If you got too much hardener in your mix, this could also accelerate the cure. What brand are you using?

 

[sandman]

LOL!

That's happened to me more than once!!

Here is a trick from the West Epoxy handbook.

After you mix your epoxy pour it into a disposable cheap aluminum pie plate.

This will dissapate any exothermic heat.

The problem arises because as the epoxy cures it is exothermic...it gives off heat...the heat causes the remaining epoxy to cure faster and give off even more heat...sortof a chain reaction.

The aluminum pie plate spreads the epoxy out and the auluminum acts like a big heat sink to dissapate the heat.

I've mixed over a quart of epoxy at a time (I build wood/epoxy boats) and this method works great especially if it's hot out.

sandman

 

[Karl]

I've been using International Epiglass Resin & Hardner , with FASTGLASS Fibre Tissue , is this the right stuff ? It's the only stuff I could find , does anyone know where I can get the right Fireglass Mating from in the UK?
Thanks
Karl

 

[wyldbill]

You want something with a slow cure time, on the order of several hours. Using fast cure epoxies will exacerbate the heat problem and not give you enough working time. IF they offer a "slow" hardener (or even a "finish" hardener) else that.

As for UK sources, I can't really help you there....

 

[Karl]

I'll use the pie tin method next time . It does have a full curing time of at least 5-8hours.
-Karl

 

[sandman]

Karl,

Full cure time is long but a long "pot life" is what you want. That's your working time. West epoxy has a "pot life" of about an hour at normal temperatures.

For small amount (about a meter square) of glass cloth SIG has a wide variety of light wt. cloth.

I don't know where it would be available in the UK but perhaps you can purchase it online.

https://www.sigmfg.com/cgi-bin/dpsmart.exe/MainMenuFV3.html?E+Sig

Go to catalog at the top. Then go to "coverings" in the menu on the left.

sandman

 

[cydermaster]

Originally posted by Karl
I've been using International Epiglass Resin & Hardner , with FASTGLASS Fibre Tissue , is this the right stuff ? It's the only stuff I could find , does anyone know where I can get the right Fireglass Mating from in the UK?

I've tried using that FASTGLASS stuff - its car bodywork repair stuff. Its designed more to be easy to finish, than strength. This got mentioned on uk.tech.rocketry about 3 days after I brought it.

The same thread provided at link to CFS ([url]www. cfsnet.co.uk).[/URL] I've not brought anything from them (yet), but I did get them to send me their catalogue - its pretty good, worth getting (its free). They do West System & that.

 

[wyldbill]

Sounds like it's a polyester resin. If so, you might want to avoid it. Epoxy resins are generally preferred in this application.