Fiberglass comes in many different styles and weights, measured in ounces per square yard.
This Fiberglass "rope" I used was actually 20 strands taken from 2 yards worth of Woven Roving. This one strand is taken from woven roving is about 1/4" wide.
Woven roving is 24 oz per square yard where as most store bought folded fiberglass is in the 6 or 8 oz range.
If you have any boatyards around they likely have some, but you might have to order it.
http://www.fiberglasssource.com/sunshop/index.php?l=product_detail&p=667.
One of the best fiberglass sites around is Thayercraft.
http://thayercraft.com/
They have incredible selection, excellent descriptions, and free fast shipping, along with excellent prices. I ordered some very lightweight very fine 1.43oz cloth from them, and did employ some in my roof repair.
Wetting this much fiberglass out ( the 'rope' ) takes time. I basically make a cardboard "panga" like a boat, and lay the preprepped fiberglass"rope' into it, and pour the mixed epoxy over it and let it absorb and expand and turn clear. Various tools to spread resin to unwet areas, and after it goes clear I pick up the end and lightly squeeze out the extra resin through gloved fingers and lay it into place. One end I have either tied in a knot or taped off, usually taped with Scotch ot 3M blue painters tape. I'll leave this portion outside the repair and when the epoxy thickens will cut it off with a new razor blades, or many of them, or wait until it is hard and use my angle grinder and a cut off wheel to cut off this portion.
If the rope is just a few strands of woven roving, I will cut them when wet with sharp scissors, but the resin must be removed from the scissors before it sets up. With epoxy a 50/50 mix of alcohol and vinegar works nice, but with polyester resin you are stuck cleaning tools with acetone, which is a pretty evil solvent and can send highly undesirable chemicals right into your bloodstream when in contact with bare skin.. Epoxy hardeners and acetone are especially dangerous.
Woven roving used as 'rope' is basically the way to get the most fiberglass fibers in any given area for maximum strength. Even if the strands go from north to south, east/west strength will be nearly that of north to south in both tensile and compressive strengths.
Filleting corners with fiberglass rope/roving is an extreme overkill version compared to using a thickening agent in resin to fill the same corner. Some thickening agents are 'bulkifiers' and make sanding easier and the resin lighter. I've been using wood flour and milled fiberglass fibers when I need to make a thickened epoxy 'Bondo'. and this is about a hundred fold stronger than store bought bondo, and much harder to sand too, so work with the putty knives/ spreaders is more important to save work later.
But lots of other thixotropic agents are available, all with their ups and downs
While epoxy slowly gets harder, polyester resins, which are easily obtained, have a working time/Pot life, and beyond that it cannot really be worked. Do not overcatalyze the ester resins. Most do.
Polyester resins are generally more resistant to heat and UV light. Epoxy Must be protected from UV though some claim to have UV inhibitors.
Both are exothermic reactions, they produce their own heat. One should not mix a batch of either and let it stay in the mixing cup. faster epoxies will start smoking, as will highly catalyzed polyester resin, so after mixing, spread it out thinner to get more working time.
Epoxy must be mixed precisely and thoroughly. Polyester resins just need a bit of catalyst and are more tolerant of over and under catalyzing and under mixing, though both should be avoided. Wrongly mixed epoxy is a nightmare to remove. It will never fully harden and will gum up sandpaper.
When working with fiberglass cloth , it is difficult to work clean, try to cut it with sharp scissors along the weave, and pull out any loose strands before you wet it out. Make sure the fibers are perpendicular as possible when cutting it and laying it in place. Pulling out loose strands can help to make sure patches are perpindicular. Fiberglass MATT, cannot be used with epoxy, only vinylester and polyester resins as it is held together by Styrenes which are only dissolved by the styrene in ester resins. Epoxy has none.
Rounding the corners can make it a lot easier to work with, although rounding the corners is not always easy. Sharp scissors are paramount. I just picked up a set of finely serrated dress makers shears, and what a difference compared to a normal set of Fiskars! Don't even try fiberglass repair if you've got dull scissors.
The 3m 5200 is incredible stuff, but cures very slow and needs humidity to do so. They have a fast cure version too, but even this cannot be considered fast. If it needs to be removed, it will fight and need to be ground off. Better to consider it permanent, but if it fails to hold, like it did on my forward roof line, then it is just a serious impediment to a proper fix later.
Once the tubing is opened you basically have to use it in a week. You can keep it in the fridge to extend this time to use it. It was designed for sealing through hull fittings, and this should be considered when using it for other tasks. I should not have used it as I did along above my windshield. Perhaps if both surfaces were super clean it might have held, but without mechanical fasteners the flexing was beyond even the mighty 3M 5200.
