Fiberglassing openings and edges

[troubleScottie]

Just starting a design and I have decided on a 5X10 woodie completely faced with 4 oz fiberglass outer skin, no paint, maybe some pinstriping.

I have looked at lots of the information here and on the marine sites as to how to do fiberglassing in general. I have no prior experience with fiberglass.

The question that one has is how to handle the openings ie door, fan, skylight openings and the "open" edges ie along the bottom edge where walls meets the floor or trailer. Assuming a thick (over 1") wall and roof, how far over or onto the edge should the fiberglass be done? For most of these openings, there will be moldings/flanges that cover the edges of the openings.

Obviously there are issues with 90 degree corners. Do you round all edges? With what ie rotor, power sander or hand sand? Assuming an outer plywood skin at 1/8", does that change anything?

How do you deal with the inside corners ie the corner of the door opening?

Do you worry about the resin getting on the interior surfaces ? ( I am good but not perfect painter ) Would you suggest finishing the interior first, then mask, then fiberglass?

How do you keep the glass/epoxy off the trailer frame? Or is that unnecessary?

Similarly how does one handle small openings -- holes for lights and wiring opening in the outer walls. Do you worry about the glass or resin getting onto the wires/cables/tubing? Most likely the rough wiring will be in place before skin is done.

Any advice on reaching in on the roof outside of longer arms and a taller ladder?

Any other advice is welcome.


Thanks in advance.

[Pmullen503]

I'll offer some advice, if this is your first experience with epoxy and glass, practice on something else first. Take some scrap plywood and cover it so you can see how much resin it takes. You don't want drips and sags but you don't want the cloth starved either. If you haven't bought your resin yet, consider a non blushing, laminating resin like Matrix Adhesive Systems. Avoid a thick resin like West System. Don't get me wrong, it's fine resin but as a beginner you risk working in small bubbles that will cure white. If you plan to use polyester resin; DON'T. I've done a lot of work with polyester over the years and can tell you that you'll have a much greater chance of success the first time with epoxy resin (you probably don't have the proper protective gear to use it safely either.)

You should round over all your edges. With 4 oz cloth, you can get away with 1/8" round over. Think twice about trying to cover the whole thing in one or two large pieces of cloth. It will be easier to use smaller pieces and the overlaps will disappear after you sand the edges and apply more epoxy. If you have a curved profile, glass up to the corners separately with glass on the side and top and then cover the corner with a strip of cloth cut on the bias (weave running at 45 degrees). That strip will follow the curve and not pucker.

You can apply resin to the wood (interior and exterior) first without any cloth. Let that cure and put cloth on the outside. That should alleviate any problems with resin drips staining the inside wood. Make sure you use a NON-BLUSHING epoxy or you'll have to scrub off the amine blush before recoating.

I wouldn't worry about wrapping the glass around the edges of openings; just trim it flush and coat that edge with more epoxy. It would be stronger if you wrapped it but if you've never done it before, it may drive you nuts to get the results you want. You can glass right over small holes, just be careful about forcing a lot of resin into the holes.

With a little practice first, you should be able to successfully glass your tear the first time.