I have been drafted as slave labor to install skid plates on my father in law's canoe. It's an old chopped fiberglass monstrosity at the summer camp that mostly gets used by the grandkids, and never travels far from the dock. Performance is not an issue, but durability is.

He got what was sold to him as a "skid plate kit" from the local canoe shop. It does not have pre-cut kevlar skid plates. I think what has is actually a fiberglass patch kit. It contains resin and hardener, about a yard of fiberglass fabric, and a similar amount of a felted fiberglass matt.

So, should I tell him to return this kit and buy an actual skidplate kit from Old Town or some other source? Or should I simply cut a pair of skid plates out of the felt and fabric, and install as directed for a patch?

Alternatively, given some of the former discussion on here about thick felted skid plates (I did do a search), should I omit the fiberglass felt and just install a layer or two of the glass cloth impregnated with the activated resin?

Yes.

Or, seriously, I hate to see him or you laying out for a Kevlar felt kit for an old FG boat that will receive only light to moderate use.

Try to use the kit you have, if possible. The FG cloth should ideally be bias-cut so that it will conform more easily to the hull convexities. That means cutting at a 45 degree angle to the fibers rather than parallel. But if the FG cloth is pre-cut and seems to lay OK "dry" on the hull, don't worry about it. I would do the FG cloth layers first, and then see if there is any need for the FG felt. I doubt it.

Again the rule is, the largest cloth layer first, and so on down to the smallest. Three, or maybe only two, layers should be enough.

If the boat is old, and kids are going to be handling it, check for areas where they might pick up little itchy fibers. These can be painted over with resin or paint.

Thanks.

Your suggestion about the largest patch first, followed by smaller ones as necessary makes sense to me. I note, however, that the directions in the kit suggest exactly the opposite--a smaller patch of the felt, with a somewhat larger (they say 1 inch larger all around) cloth patch over that.

Trying to cut up that felted mat does not look like fun, so I'm sticking with a couple of layers of the cloth unless someone can provide a good reason to use the felt.

I figure if I can get the patches on this weekend, I will be the favorite son-in-law for at least a couple of family gatherings.

Yeah, the largest-patch-first approach has a sound structural basis, but it's hard for me to explain. It was the patching approach recommended in the old "Boatbuilder's Manual" by Charlie Wallbridge. I think people try the smallest patch first method in the hopes of getting a smoother result, but the ridges may still show, and when you sand them, you're cutting structural bonds rather than just cloth margin.

Yes, I tried to make this case on the current canoe fiberglassing thread in regard to doubling up the glass on a stripper bottom with an extra football shaped piece. Lacking a diagram, I couldn't really show what I meant.

When the small piece goes on the outside, its edges can be feathered without any ill effect. When the large piece covers the smaller one, any attempt to fair the overlap without the use of fairing compound may result in the outer piece being sanded right through. When this happens, there will be no structural support at all along the line that gets sanded away as all of the fibers will be severed.

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Hearing no votes for using the felted fiberglass mat, I am planning to install 2-3 layers of the glass cloth, largest first, as discussed above.

Does it matter if I allow the resin to set up between layers, or can I install them all at once and allow the whole assembly to cure together?

Assuming the resin is thin (like West 105/205), you can wet out the first layer, and then plunk the next layer on top of the first. The second layer will draw excess resin out of the first, and then you can wet out any dry looking spots. If you do a third layer, you should be able to plunk that onto the second and continue.

Then if the resin is still fluid, you can drop a sheet of Glad Wrap or similar food wrap film over the layers. If your patch is not laying over convexity, you can use electrical or other stretchy tape bits to pull the film outward gently in every direction. This will squeeze out some extra resin. You can gently use your finger to work out bubbles or excess resin from under the film. Don't be fussy, it's an ugly canoe.

When the patch is hard, you can sand any rough spots, trying not to cut into structural strands. Later if you have some varnish with UV inhibitor, you can paint over the resin.

Now, if your family pulls you away before you get the secod patch on, or if the resin "goes off," (unlikely in Maine), then let the first layer harden. Wash it with detergent and a brush to remove the amine blush that would interfere with adhesion of more layers. Sand lightly, and proceed to mix more epoxy and do the remaining layers.

You can use West G-flex for this if you want, rather than a pump resin like 105/205. But G-flex is thicker, a little harder to work into the cloth, and needs the better part of a day before it gets "hard." Further hardening occurs over a couple of weeks. It is tougher and more flexible than 105/205.