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Old 12-28-2007, 10:00 AM
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Fiberglass top fab questions

Hey guys,
After some soul searching, I've decided to finish my first project before I really dig in on the '50 chevy. I hope it's not to off topic, and someone with fiberglass experience wouldn't mind chiming in.

The steel top on my jeepster has been under the knife more times than I care to remember. I chopped it down several years ago after several failed attempts to straighten it out, fix rust holes and cracks.

I'm toying with the idea of building a new fiberglass top for it. I've been researching and testing a few materials. Home Despot has urethane foam sheets 1" thick that normal polyester resin doesn't melt.
I think I can shape the sheets to a reasonable form, glass both sides of the foam, then a bit of bondo on the outside to smooth it off.
I've found references saying "layup" resin is better because it doen't have wax in it. Or does that really matter?
Any tips for the matte weight I should look for?

Thanks for your help
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Old 12-28-2007, 10:30 AM
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If it has wax,That means you will have to sand a piece that you glassed to add more later,With no wax you Don't have to sand it,Just wipe it down with acetone.(Just make sure there is no little Pieces sticking up that will not let the glass lay flat.)Did you think about poping a mold off of your top.That may be the way to go.
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Old 12-28-2007, 10:39 AM
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Well, that makes perfect sense! Thanks
I take it that the usual resin contains wax, and I should look for "layup" right?

Quote:
Originally Posted by NEW INTERIORS
Did you think about poping a mold off of your top.That may be the way to go.
I did, but this top is really wavy (5 big holes brazed up on the very top) and ill fitting as it is cause I think it was flopped over before I got it.

That and it's heavy and awkward to remove. I think I can make it into a few sections so I can pull it 1 part at a time and store it easier.
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Old 12-28-2007, 10:47 AM
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All i use is the Polyester Resin.As for the holes I just duck tape them close And go for it.(If you can get it striate enough)I built a whole 32 Chevy with duck tape and card board as a mold. Speedy is also very good with glass.He would also be glad to help you.
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Old 12-28-2007, 11:21 AM
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"Normal" resin does not contain wax. "laminating" resin is what we call it around here, . "Sanding" resin contains wax or some other kind of surficant.

The reason is that polyester resin is formulated to NOT surface cure in the presence of oxygen. Secondary laminations don't adhere well to cured resin, and just sanding it only allows a mechanical bond. When you lay laminating resin over a part previously layed up with laminating resin, it creates a chemical bond, as well as a mechanical one.



Don't use sanding resin on anything other than something you want resin to be your finished surface on, such as a surfboard or table top.

You could use your current top as a plug to make your mold, if you can dummy up the shape good enough to paint with resin or duratec and remain dimensionally stable during the mold making process.


I usually use 1 1/2 oz matt, it seems to be a good weight and bends reasonably well.

One thing you need to consider is how you will attach the top to your body. If you have return flanges, you need to consider these before you start your mold making process.


Doing a one off part will work with the urethane foam, but you'll want to get rid of the foam after laying up over the outside of it, doing both sides, it will eventually dissolve inside your laminate, a phenomenon they call core shear.

There is a bunch of info here on the site, do a search for "fiberglass".

Here is one good one with a couple of good links.
Making a Fiberglass body


Later, mikey
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Old 12-28-2007, 12:09 PM
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It is true most resins you buy at a store like walmart have wax. I buy what around here is called production resin which has no wax. This is what you want.There are many ways to make a one off part. If you are good at carpentry you can make a mold sort of like building a boat inside out. Form your shape with ribs and layer the inside with bathroom masonite.This is the one with the formica like finish. that way when you build your part the outside will be smooth already.It is not needed but highly recommended to use gelcoat as your outer layer. Once you have made your mold, wax it good with mold release wax. Then spray or brush your gelcoat on mixing twice the hardener recommended. This is to make it start curing before it can eat through the wax.Once this has cured preferably overnight you can put your first layer off cloth.Get a fiber glass roller to smooth out the air bubbles this is critical on your first layer.Also mix this first layer double hardener. Don't worry as if you tear the cloth instead of cutting it you can do a small portion at a time so you don't have to rush. Just make sure you wet out the cloth all the way to the end or when it cures it will lift.If you get this far let me know and I will steer you further.
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Old 12-28-2007, 12:36 PM
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You don't "tear" fiberglass cloth. You can tear matt.
Cloth and matt are two different types of fiberglass fabric. Cloth is woven strands, while matt is made from gun roving with a chopper gun and sprayed with a shellac binder to hold it together intil it gets wetted out.

You don't want to add twice the reccomended hardener to any resin product. Gelcoat will crack and prerelease from your mold if you overcatalyze it.

Gelcoat does not eat into wax. The wax is non reactive with styrene and polyesters.
That's why they use wax as a release agent.

If you want to spray gelcoat , you should only thin it with styrene, not acetone or laquer thinner.

I never add more than 10% styrene to gelcoat and then spray it with a pressure pot, not a suction type gun.




Later, mikey
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Old 12-28-2007, 12:40 PM
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Check out this site,And see what they call mat.

www.fiberglasswarehouse.com


Good point Mikey!!

Last edited by NEW INTERIORS; 12-28-2007 at 12:46 PM.
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Old 12-28-2007, 01:04 PM
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Mike I am sorry if we use different terms down south. When I said tear the cloth I was refering to the matt cloth as we call it. I have built many boats and fiberglass race car body parts over the last 25 years using the method I described, If they don't work the same in california I am sorry, but they work great down here as many drag racers running my parts or have had parts repaired by me will attest to.I have shipped parts all over the country and have not had 1 complaint.When I spray gelcoat into a mold I don't thin it I use a special gun for gelcoat.

Last edited by speedydeedy; 12-28-2007 at 01:07 PM. Reason: Add info
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Old 12-28-2007, 02:16 PM
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Dang, too much info LOL
Here is were I got the idea of leaving the foam inside
http://www.rqriley.com/frp-foam.htm
I just may have to rethink that. I thought it was a good idea after looking at stock cj glass tops, and how flimsy they are.

I'm still leaning twards making the basic shape out of foam, actually on the jeep for the perfict fit.
Then like 2 layers of random mat on the outside?
whittle the foam out, then like 2 layers of woven cloth inside?
Or do I have that basakwards?

Thanks for the info still trying to wrap my mind around the details.
Happy New Year!
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Old 12-28-2007, 02:22 PM
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Quote:
Originally Posted by speedydeedy
Mike I am sorry if we use different terms down south. When I said tear the cloth I was refering to the matt cloth as we call it. I have built many boats and fiberglass race car body parts over the last 25 years using the method I described, If they don't work the same in california I am sorry, but they work great down here as many drag racers running my parts or have had parts repaired by me will attest to.I have shipped parts all over the country and have not had 1 complaint.When I spray gelcoat into a mold I don't thin it I use a special gun for gelcoat.
I'm sorry to correct your mistakes but if you are trying to communicate to someone who is not knowledgeable about fiberglass you don't use words that are easily misunderstood to mean something else. .And you don't give them disinformation, such as :


Quote:
Originally Posted by speedydeedy
Then spray or brush your gelcoat on mixing twice the hardener recommended. This is to make it start curing before it can eat through the wax.
There is a reason why they have a range of catalyzation levels, and why you don't add more than the recommended amount. If you want the resin or gelcoat to cure faster, you go to a hotter catalyst.

I too have been building fiberglass parts, but only for 22 years, everything I learned was from working full time at a full service fiberglass shop for 13 years. (Poli-Form Industries, Watsonville, Ca), Our parts were shipped all over the world, and the man I learned from has been building things out of 'glass since 1948.

If you want to disinform people, then expect to be corrected.

And don't blame it on your location.


Later, mikey
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Old 12-28-2007, 02:34 PM
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Quote:
Originally Posted by Thommyknocker
Dang, too much info LOL
Here is were I got the idea of leaving the foam inside
http://www.rqriley.com/frp-foam.htm
I just may have to rethink that. I thought it was a good idea after looking at stock cj glass tops, and how flimsy they are.

I'm still leaning twards making the basic shape out of foam, actually on the jeep for the perfict fit.
Then like 2 layers of random mat on the outside?
whittle the foam out, then like 2 layers of woven cloth inside?
Or do I have that basakwards?

Thanks for the info still trying to wrap my mind around the details.
Happy New Year!
That would work, but I'd use 3 layers of 1 1/2 oz matt on the outside, let it cure, then whittle out the foam out from inside.

You can use high density foam like clarkfoam and leave it in, but the home depot stuff is too crumbly to use like that.

Put another layer of 1 1/2 oz mat on the inside, and on top of that some coremat or 1/8" high density urethane foam on the flat areas, then glass over them with another 2 layers of matt.

For what you are doing, I'd leave the cloth out.

You don't want cloth on the outside, it is a pain to sand without cutting into the fibers, and it'll transfer it's pattern to the surface.


Later, mikey
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Old 12-28-2007, 03:55 PM
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Quote:
Originally Posted by powerrodsmike
That would work, but I'd use 3 layers of 1 1/2 oz matt on the outside, let it cure, then whittle out the foam out from inside.

You can use high density foam like clarkfoam and leave it in, but the home depot stuff is too crumbly to use like that.

Put another layer of 1 1/2 oz mat on the inside, and on top of that some coremat or 1/8" high density urethane foam on the flat areas, then glass over them with another 2 layers of matt.

For what you are doing, I'd leave the cloth out.

You don't want cloth on the outside, it is a pain to sand without cutting into the fibers, and it'll transfer it's pattern to the surface.


Later, Mikey
Mikey is right,I would never put cloth on the good side of your part,big no!no!
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Old 12-28-2007, 05:18 PM
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quick question, what would be a good releasing agent from a foam mold?
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Old 12-28-2007, 05:40 PM
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Foam molds don't do well by themselves, you should really lay up a couple layers of glass then paint it with resin or duratec primer

If I make a foam buck, knowing I'm going to use it once, I will usually coat it with resin, let the resin cure, then I'll wax it with green wax and follow that with a sprayed coat of Poly Vinyl Alcohol, (PVA)

This will get the glass part to separate really easily from the foam .You'll wreck the foam getting it off, but the part will be relatively smooth on the inside.

Check out the wiki that I wrote about making a fiberglass fan shroud. All of those techniques can be applied to one off 'glass parts.

http://crankshaftcoalition.com/wiki/...***_fan_shroud

I need to do some more like that.

Later, mikey
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