Small Repair: Weave or Chop?

[PeteCress]

This: http://tinyurl.com/8lqnupc

Strip-built, cedar encapsulated fiberglass.

Understood that the upper area needs more feathering.

Would you lay woven cloth over it and then sand down the result?

Or would you smooth a mix of chopped glass and resin over it and call it a day?

[Tom Hunter]

I would do the cloth and sand route, because its not going to take long at all. If you fill with chopped glass you may still have to sand it.

[PeteCress]

If you fill with chopped glass you may still have to sand it.

What about strength? Is there a diff?

If I put chopped glass in there, cover it with clear packing tape, and then squeegee it will come out very smooth: almost zero sanding except for feathering the resin where the masking tape was pulled.

OTOH, I have no clue about relative stengths.

[Todd Bradshaw]

I think that would depend on the amount of prep you do. If you feather the surrounding area out nicely, you're probably going to end up with a spot that's a couple inches in diameter needing new reinforcement and cloth is probably the best way to do it (and strongest). Chopped short strands tend to be rather brittle and weak. On the other hand, if you decide that the edges of the current holes are sound (not delaminated or fractured, which they don't appear to be) you could probably plug in a blob of resin and strands and be good to go for the duration. Given the option, I'd rather cut my own strands to the lengths I need to span the holes, by unraveling them from a hunk of scrap cloth or roving and just pack the holes pretty full with them while saturating them with a small brush. The "woven" part of woven cloth isn't what's contributing the strength, it's just a convenient way to handle and apply individual, high tensile strength continuous strands of glass fiber and they are what is doing the work. In any case, the actual holes here are so small that I doubt they will ever give you any trouble as long as you maintain the water-seal of the epoxy.

[PeteCress]

The "woven" part of woven cloth isn't what's contributing the strength, it's just a convenient way to handle and apply individual, high tensile strength continuous strands of glass fiber and they are what is doing the work.

I think that addresses the question that I should have asked in the first place.

Thanks!

[JimConlin]

I'd use cloth.
Glass cloth of the weight typically used on canoes might have 15-20 threads per inch, in two directions.
Laying sticky threads down with that spacing sounds tedious and unlikely.
While the woven nature of cloth makes it slightly less stiff than straight strands, it helps a lot in getting the whole mess to lay flat.

Chopped glass fiber in epoxy will be either weak and brittle if mixed resin-rich or hard to form if dryer .

A bit of peel-ply (or nylon taffeta lining) over the whole sticky mess will make it a lot easier to squeegee flat.

[Todd Bradshaw]

All you do is brush-in a light coat of resin with a small brush, grab some of your cut strands (with tweezers if needed) and lay them into the wet resin. Then you stipple them down and add a little more resin as needed (brushing with the lay). Put down some more strands (either the same direction or aimed 90 degrees the other direction, or even 45 degrees if you want to mimic the old Moore Canoe Company "Octo-metric Layup") and stipple them down with a bit more resin as needed. Continue until you have filled the hole and saturated the strands properly. It's pretty much the same way you would apply graphite tows. With holes that small, it shouldn't take more than about ten minutes per hole.

We used to also use this technique for making small, bomb-proof fillets in applications like the joints between flotation tank walls and the insides of the hull. We used the big strands, raveled-out from the edges of a hunk of fiberglass roving that were sometimes as long as six feet or so, and we might be using six to ten strands to reinforce a 1/4" thick fillet. It made a very strong joint with a small amount of material and unlike typical fillet fillers, they were clear and blended in pretty well to the surrounding color. If you're building strippers, you should invest in a yard or two of 24 oz. woven roving. Every once in a while a situation comes up where this type of reinforcement is just what the doctor ordered.

Back in the days of wooden cross-country skis, I used the same technique (WEST 105/205 and roving strands) to replace torn out sections of Lignostone ski edges in our repair shop. As long as you do your brushing with the lay of the strands, it's pretty simple and quite strong.

[PeteCress]

A bit of peel-ply (or nylon taffeta lining) over the whole sticky mess will make it a lot easier to squeegee flat.

I've been using 2" clear cellophane tape - more because it's at hand than anything else.

I guess I'm introducing an additional need for sanding (contamination with the tape's adhesive) after the resin is hard, but other than that it seems to work pretty well, and I usually have to sand some anyhow.