Fiberglassing

[Treadhead]

I've been considering fiberglassing more and more these days. But I have some questions...

1. From what I've read, the gel coat mostly used is polyester resin. Why is this?

2. Are there commercially available gel coats and what's the best one?

3. For a gel coat, could I get the SmoothOn 300 stuff and just add talc? I've heard great things about this particular resin.

Thanks in advance for your help...

[modelnutz]

A few answers for ya....

Polyester gel coat is used because the laminating resin most used is polyester....it's a compatability thing....polyester sticks to polyester really well. FYI...gel coat is standard resin with the addition of styrene wax...during curing, the styrene wax migrates to the surface preventing air from reaching the resin...this allows the resin to fully cure to a sandable state...without wax, the resin will remain "sticky"...waiting for the next coat.

Yes, gel coats are a standard item.....you might try Fiberglast for your materials....very good supplier...they have everything you'll need.

Smooth-On SC-300 is a polyURETHANE...not polyESTER...totally different animal. You may not get a decent bond between layers.

Having said that...I will say that you can use SC-300 as a fiberglass resin...it works pretty well and makes a rigid part that is easy to sand and glue...downside is the cost...Polyester resin is CHEAP..that's one reason it's so prevailent. Also, and this is something to consider...Polyester resin is designed to work with fiberglass...the resin has a component that acts to soften the binder used on glass cloth and matt...this makes the glass much easyer to push into place.

Be aware also, polyester is a very hot resin...it will burn up a silicone mold much faster than urethanes....you might want to consider using Smooth-On;s PMS line of urethane rubbers for your mold material...lower cost..and a decent lifespan.

And...please...for the sake of your health...WEAR AN APPOVED RESPERATOR !!! Polyester is a brain destroying chemical.....pay for a good mask...it's well worth the money!

[Treadhead]

Thanks Modelnutz...

The thing that kinda scares me away from polyester resin is that it's supposed to shrink like crazy compared to other resins. Would the fiberglassing mitigage this problem?

If I wanted to go with the smooth on stuff -- could I use talc to thicken up the SC300 and use it as a gelcoat?

[Dr. Yo]

I haven't done any fiberglass work myself, but I've heard Vince Hoffman
talk about using a thirty minute epoxy for the lay up, and he seems
pretty satisfied with it. I remember my brothers building surfboards with
glass and polyester resin when I was a kid in the '60s, and the stuff is
pretty toxic...

Any thoughts on that, Ed?

[modelnutz]

Thanks Modelnutz...

The thing that kinda scares me away from polyester resin is that it's supposed to shrink like crazy compared to other resins. Would the fiberglassing mitigage this problem? Working to a high glass to resin ratio helps limit the shrinkage...but...it's always going to shrink some.If I wanted to go with the smooth on stuff -- could I use talc to thicken up the SC300 and use it as a gelcoat?

It probably wouldn't work too well as a gel coat...if you were going to follow up with polyester resin....they just don't stick to each other that well.

Talc would work as a thickening agent....but you would have to use a ton of it to get the paste like results you're looking for....better to go with Smooth-On's "Shell Shock"...it's a trowelable resin that's a seriously tough plastic.

I might be inclined to follow the good Doctor's lead...Epoxy ( laminating epoxy that is...also sold at Fiberglast ) is a very good resin for fiberglassing..I believe that's what REL's using as well...just be sure to use a good mask with that as well...it's not as toxic as Polyester ( which is VERY NASTY stuff )...but, some people develop a tolerance issue with epoxy...you'll start to have problems breathing....never a good thing ;-)

[Space Garbageman]

Agreed, look into using epoxy for laminating. It has a better (longer) working time than polyester and it doesn't shrink. It's also stronger and won't have that sticky surface. It can also be thinned up to 30% with methanol after its been mixed, this can help to work it into the fibers. You can clean up your brushes and mixing containers with methanol when finished. More expensive than polyester, though.
There's no gel coat, as such, with epoxy. 'Course, if you're planning to do a lot of finishing on the surface of the completed part (priming, painting, etc.) then you wouldn't need a gel coat, anyway. Unless I'm mistaken, gel coats are intended as the surface finish.
Look into the different types of mat materials, as well. There are some ultra-fine woven mats that are intended for use with the lower viscosity resins, like epoxy. An alternative to the chopped strand mat, anyway.
I wouldn't try using SM-300 for laminating. The stuff goes off so fast I think it might be too much to handle. Don't know why it wouldn't work in theory, just seem like a lot of trouble.

[modelnut]

I am glad I ran across this thread. I am planning to glass a submarine hull in the (hopefully) not too distant future. You fellows have given me more information that I have received from another board I directly asked my questions on.

I think the problem is that they work with it so much that they talk in shorthand. Not very useful for the novice.


- Leelan

[modelnut]

About fiberglass's toxicity . . .

It sounds like my plan to glass in my studio isn't as safe as I thought from what you are saying. I used to live in a one room apartment. I knew better than to try it there. But it sounds like maybe I shouldn't even do it in the house.

If I have to do it outside then I need to wait until the 100 degree weather passes. I have a back porch and its shaded.

- Leelan

[Space Garbageman]

That's a good idea. If you're using polyestyer, get yourself a respirator rated for painting cars (basically any charcoal-filtered mask, one rated for VOC's- volatile organic compounds). Not as much of an issue with epoxy, though, but nothing wrong with being safer, either.