Smooth epoxy/fiberglass layup
 

In the past, it took several fill coats and sanding or expensive vacuum bagging gear to get a smooth layup.
The "drier" you can lay up glass, the stronger it is by weight. The trouble comes when you want a smooth finish. If you sand a typical dry layup, you will sand right into the glass itself. The old solution is to add as many fill coats as necessary to cover the glass and get a sandable margin.
Recently I found this simple method to get quick results.
Lay up your glass as you normally do, them apply a film of 10 mil mylar or similar plastic over the wet epoxy, squeegee out any air bubbles and excess resin, and let cure.
Once cured you can peel off the mylar.
What the film does is compact the layup, squeeze out excess resin, and leave a surface as smooth as the mylar itself.
I have not done any large areas yet, since my current project involves only resin coating with no glass.
I used 4 once E-glass over some scraps of virola marine plywood. 4 ounce is about as heavy as you can go and achieve a transparent layup over wood.

Wet layup:
http://i810.photobucket.com/albums/z...y/epoxy001.jpg

Mylar placed over one section of glass:
http://i810.photobucket.com/albums/z...y/epoxy003.jpg

Air and excess squeezed out with plastic squeegee:
http://i810.photobucket.com/albums/z...y/epoxy004.jpg

results from previous sample. Part of the sample was left as usual with the fabric weave showing.
http://i810.photobucket.com/albums/z...y/epoxy007.jpg

That is a reflection of the trees in our yard out the window.

Another view:

http://i810.photobucket.com/albums/z...y/epoxy006.jpg

This was junk resin. You can see some small bubbles in the otherwise glass smooth surface. I think those were from the foam in the resin, I literally wrung out the paint roller to get some resin to make this sample. it was frothy white in the cup.

What you can do with it:
Bend over large radii.

What you can't do with it:
lay over a compound curve in a single piece. It will not warp in two directions.
The answer is to use strips and butt them together. This will form some small raised seams in the finish. You can cut those off with fine grit paper.

This is where I found it:
A new Technique for Epoxy-Glass
I figure this could be handy for building aeroshells, etc.

Wow! The 'finished' pics are after you removed the mylar?? A-Ma-Zing!!

The lack of a smooth finish has always been one of the reasons I disliked doing 'straight fiberglass' on the outside of a project... always thought the only way to get a decent smooth finish was to build a mold first... a bit more work than I wanted to do for a large one-off part... but this approach is so straightforward and simple... Awesome!!

Thank you for sharing!

You are welcome.
Looks like the mylar is still on there, doesn't it ?
I'll pull that other sample in the first pics in the morning and post that too.

[QUOTE=skyking;291010]A related technique, used with epoxy, is covering the layup with peel ply, which can be formed into a compound curve. This leaves a surface that permits secondary bonding without the need for sanding. But it also permits light sanding, in preparation for painting, without getting down to the glass. Sanding with 150 grit, then using a high fill primer and one sanding of that is usually enough prep for finish painting.

Bubbles might be a little easier to work out of peel ply. Both techniques can be useful for different conditions. (Peel ply replaces the fiberglass fabric weave surface with a much finer dacron weave, which is not glossy.)

Thanks Ken. I have used peel ply in the past, usually for preparing for a subsequent additional layup.

skyking ,Thanks for your in depth post on this.
I am going to try this technique on my fiberglass/foam truck camper build. Anyone have a cheap source for Mylar? I already tried the rolled polyethylene from Home Depot and it seems to stretch under the squeegee and leave a less than flat surface. Also, what was the thickness of the Mylar you used.

I purchased it at a fiberglass supply house for ~$3 a running foot, 48" wide. It seems to be about 10 Mil. I am trying out some HDPE today. If it releases as well I think I have a decent source for it. I recently purchased coroplast from a nearby vendor who also has rolls of this HDPE.

Another approach that works better than Mylar, is Glad Wrap.

It's much more flexible, is thin, and works as an excellent mold release.

Jim.

The glad wrap easily wrinkles and does not transmit a flat surface onto your job. It does work as mold release and I use it to put under parts I don't want stuck to the table.

[QUOTE=Ken Fry;291021]Ken, I have learned that peel ply is Polyester Taffeta at the discount fabric store :)
I am buying some for $2.45 per yard in 48" width to do some testing.