Glassing thru-hulls side by side

[minaret]

Originally Posted by sailvayu

Another reason not to use the largest piece first is as clearly seen in minaret's drawing. All the fiber ends are pointing out and exposed to the water allowing moisture to wick into the repair. With using the smaller pieces first and finishing off with a couple of mat layers (as the boat was built) when you smooth the repair down you will only be exposing some random fibers that down not go far into the laminate.

Most will agree WEST is a good resin but it was not developed for fiberglass repair. WEST stands for "Wood Epoxy Saturation Technique." The Gougeon Bros are great at marketing but are better known for building cold molded Wood boats.

All I can recommend is how I would do this on my own boat and I would start with the smaller pieces (as all pros I know do) and use polyester resin (just like the boat is built with). I would however finish off with a epoxy barrier coat as this will be under water. Guess the OP can review all this and make up their own mind as to how to proceed.

Exactly. I too would not use epoxy for this, for many reasons. Someday I'll post some pics of how I make a pattern for glass cutting. Matching fiber orientation is important. Not only should the fibers be parallel to the surface, but you should also match roving to roving, matt to matt. Once you have scheduled back a repair this is actually fairly simple and easy. Finishing with matt for grinding fair does indeed reproduce the original layup in most cases, as does sealing and final fairing in gelcoat primer, followed by barrier coat. If you are such a terrible laminator that you build a giant high into the repair with small pieces before laying down some big ones (the only way you will grind the middle fibers out of the big pieces), you should consider paying a pro instead. Keep a batten handy while glassing so you know when the repair is approaching flush. Personally I've been doing this so long my patterns tend to have exactly the right number of lams to end up just a hair proud, which is easier to fair than a low, IMHO. Another point with thru hulls is that you really don't need to back grind that far. I see people taking through hull repairs too far all the time. What I do is hot glue a piece of p lam (tape works too) to the inside of the hole for release and fill it with thixotropic resin. Then grind back both inside and out. Do about a 1/4-3/8 (depending on the boat) deep on the outside, just grind off the gel on the inside. Then do a nice structural layup outside, and glass the inside with a light layup like a few matts and a single DB. Fair and coat, and your good to go. It's much better because this keeps the repair small, instead of making a giant repair in your boat bottom where you don't need one. I've done hundreds of thru hulls this way, never had anything approaching a failure. In areas with multiple holes close together I do tend to grind the outside layup a little deeper though.