Paul Eastham

Paul Eastham

Well Known Member
Hey fiberglass experts,
I'm using West System epoxy with the slow hardener for all of the usual non-structural RV things: emp tips, airbox, miscellaneous filler, etc.

I noticed that my work would cure (or nearly so) if I put it out in the sun for an hour, instead of the usual 24+ hours. Taking that a step further, I have used a little bit of heat gun to accelerate small micro buildups and the like, with pleasing results.

I'm curious if there's much downside to doing this. The only thing I could think of is an inhalation hazard from the accelerated outgassing. This is mostly a theoretical question for me, since I don't really care about the structural integrity of my micro fillets :)

Paul
 
I used fast

and stuck some parts in the oven...Much to my Wife's dispair...Hardens in about 3 minutes...:). Hey the oven was warm with her pies she was cooking so why waste free energy?

I've seen some guys use microwave ovens too.

Sure hope there is no downside....I've cooked a lot of parts this way.

Frank
 
This is hearsay only--------I am not a chemist, but I have been told that part of the strength of epoxy is that it forms "Long chain" molecules while curing----and that accelerating the cure can interfere with this process.

Any body out there with a chemistry backgorund have input??

Mike
 
There's no real downside as long as you're not going nuts with it. I wouldn't use a heat gun because it's way too easy to overheat the epoxy and cause poor curing (or damage/warp the underlying layups). If you do use a heat gun, use it very carefully.

In general, though, there are different formulations of epoxy that are designed to be cured in an oven. Many of them use a combination of UV/Heat curing and are designed as such (they're stored in a very cold freezer).

Leaving it out in the sun is a FINE idea. A couple of heat lamps is probably a OK too. Unless you really know what you're doing, I'd stay away from the heat gun and ovens. Since none of this is structural, I guess you can tolerate some weakening.

If all you want to do is get the micro to flow a little bit better, a hair dryer works just as well. A trick I use to fill pin holes is to spread raw epoxy over the piece and then hit it with a hair dryer or heat gun (VERY gently) and it magically flows into the holes and fills them.

Bottom line: Except for micro, and filling pin holes, I wouldn't heat it much past 100 or 120F (equivalent of a really hot summer day out here in the Antelope Valley) unless you really know what you're doing.
 
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You can call Gougeon Brothers (West) at 866-937-8797 and they'll answer whatever questions you have. They were extremely helpful with lots of (free) technical advice for a major structural repair I made to my boat.
 
John is right about the 100-120F range. Make a box out of some Home Depot insulating foam sheets. Put a 60Watt lightbulb in it.
Use a meat thermometer to monitor the temp. Cut small holes in the top to regulate the temp if it gets hotter than 130F.
After a layup, put the part in the 'oven' (the box you made).
 
Mike S said:
This is hearsay only--------I am not a chemist, but I have been told that part of the strength of epoxy is that it forms "Long chain" molecules while curing----and that accelerating the cure can interfere with this process.

Any body out there with a chemistry backgorund have input??

Mike
Click to expand...

That is what I learned at composite school at the airlines.. Rapid curing makes the part brittle and prone to cracking. a heat lamp ( 18 to 24 inchs away from the part)can be used during the cure... Outside with the sun as a heat source would be acceptable.
 
Thanks for the replies. Here are a few warnings in case others want to try this:

1. If the epoxy has not yet started to gel, the heat (even just a little from the sun) will make the epoxy become more fluid. This can cause fillets or even layers of fiberglass to go sliding down and off the work. Wastes the job, and can ruin your table or deck.

2. You can get an uneven cure on thicker buildups, especially if using artificial heat sources. Cured layer with uncured layer underneath. Uncured epoxy in airborne sanding dust = danger. And not so good for sanding.
 
Thanks

RV505 said:
That is what I learned at composite school at the airlines.. Rapid curing makes the part brittle and prone to cracking. a heat lamp ( 18 to 24 inchs away from the part)can be used during the cure... Outside with the sun as a heat source would be acceptable.
Click to expand...

About what I remembered----------warming to lower viscosity---OK, gentle heating to "Post cure"---OK, high heat to "ACCELERATE" CURE-----bad.

Mike
 
Seems like a pretty wide scatter of shots on this one. Epoxy curing is a chemical reaction. Adding heat to most checmical reactions speeds the reaction. You want all the molecules to react.

To recommend heating after the cure seems odd. Guess this would help the last unreacted molecules to completely react.

I'm not so sure speed of reaction is as significant as controlling the heat within the structure. Reaction too fast could result in high temps causing damage.

Many times, epoxy resin is cured under heat and/or pressure. Temps as high as 350-f or more. Depends on the resin and mix.

Generally, I can't see where 125-150-F would hurt, but the best bet is to check with the resin manufacturer. Good idea on the box with light bulb.
 
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Mike S said:
About what I remembered----------warming to lower viscosity---OK, gentle heating to "Post cure"---OK, high heat to "ACCELERATE" CURE-----bad.

Mike
Click to expand...

Gentle heating in the 100-120F range will assist the cure. The heat will promote the chemical reaction (exotherming). Remember, this is after the part layup (after mixing epoxy at room temperature). Warming to lower the viscosity is usually done around 80F. The resin and hardener may start to exotherm immediately if the temperature is higher than 85F.
Even doing the 'warm cure', the part will take 6-8 hours to fully harden.
 
Data Sheets

You could use the manufacture's data.....

http://www.westsystem.com/frames/tier2/usingepoxy/usermanual.htm

It seems like 120F is the upper limit, and not to heat too much until the epoxy has gelled - which makes sense to prevent the "running" previously mentioned.

The volume involved makes a difference due to exothermic reactions, but I guess we are talking about relatively thin layers here....

Read the data sheets..... :D

13 responses, and no-one looked for the data sheet.... :rolleyes:

Another one for my Copperstate Safety presentation....

gil in Tucson
 
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Low Pass said:
To recommend heating after the cure seems odd.

QUOTE]

Not always. Room temp cured systems tend to get soft when the skin temp goes above the original cure temperature.

In the EZ world, the only paint color recommended was white because any other color would absorb heat in direct sun light and could cause structure movement. A white surface does not heat up much above the OAT.

There was a procedure to deliberately recure the item by covering it with a dark colored paper and curing it to a higher temperature, but I don't know of anyone doing it.

Oven cured structures are very stable.

Heat will speed up the cure process, but it needs to be done carefully, especially if the lay up is over a foam core because the foam will melt away from the glass.

dd
Click to expand...
 
It's Okay

As someone mentioned it is fine as long as you don't go to crazy. 120 is about as high as you'd want to go. DON'T USE A HEAT GUN!!!! It will gel the epoxy and never cure properly.

We often use a heat box when vacuum bagging parts. A light bulb is the heat medium. A card board build to the size you need works great.

In AZ in the summer it is not unusual to have my hangar temps at 100+. So epoxy goes off pretty fast.
 
az_gila said:
You could use the manufacture's data.....

http://www.westsystem.com/frames/tier2/usingepoxy/usermanual.htm

It seems like 120F is the upper limit, and not to heat too much until the epoxy has gelled - which makes sense to prevent the "running" previously mentioned.

The volume involved makes a difference due to exothermic reactions, but I guess we are talking about relatively thin layers here....

Read the data sheets..... :D

13 responses, and no-one looked for the data sheet.... :rolleyes:

Another one for my Copperstate Safety presentation....

gil in Tucson
Click to expand...

Since were getting technical! :rolleyes: You have to weigh the fabric and then weigh the cloth to have a even ratio. You don't want your fiberglass to have to much resin. There is no strength in the resin. The way we did it in the shop was spread out a peice of plastic, lay the cloth on it and then pour on the resin ( with hardener ). Then you lay another sheet of plastic on top and take a plastic scraper and work the resin into the glass. It saves you from having to weigh it and now you have almost a perfect glass/resin ratio. You then take your shears and cut the sandwiched glass into any shape you want. Take a razor knife and peel one side of the plastic away and apply it to the desired location. The pull the outer layer of plastic off. DONE! OR paint your area your going to glass with resin and the apply your fiberglass cloth and then put peel ply on it. When it cures pull it off, a little light prep and your ready to paint. No matter how thin it is you do not want to apply alot of heat and force the cure. Yes some cures get around 350 degrees but that requires a autoclave. BY THE WAY I"M SELLING PEEL PLY ON EBAY http://cgi.ebay.com/ebaymotors/ws/e...m=290030697976&ih=019&sspagename=STRK:MESE:IT
 
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And whatever you do

make sure your Wife's pies have been removed from the oven first.

She got really annoyed at me for putting the parts in with the pies for some reason???

Frank
 
David-aviator said:
Not always. Room temp cured systems tend to get soft when the skin temp goes above the original cure temperature.
Click to expand...
Thanks for the info. As for the oven and fumes, I've been busted a couple of times for "baking" in the oven. Wife just has no appreciation for it, at all!
 
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