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Aluminum Etch Kit necessary?

Question:
I'm using West System 2 part epoxy to attach some marine plywood to my aluminum boat. If the aluminum is clean and sanded to give a rough surface texture is it necessary to use the West System Aluminum Etch Kit to get a good bond?


Answer:
-Here is what I did when bonding fiberglass to aluminum according the manufacturer of the kitplane (Pulsar) I was building.

Rough sand the aluminum (I forget the grit) Immediately, Wipe clean, and Spread a thin layer of epoxy on the aluminum "Wet sand" the aluminum with rough sandpaper (ditto) Apply the fiberglass part using thickened epoxy.

The problem with bonding aluminum is that apparently epoxy doesn't stick well to aluminum oxide. Unfortunately, when you sand off the oxide it replaces itself virtually instantly. The idea of the "wet sanding" was to exclude air from oxidizing the newly exposed aluminum as the sandpaper removed the thin oxide layer formed after the initial sanding. The bits of sanded off oxide would remain suspended in the epoxy.

This method was only used on non-structural parts. Any structural parts had a fiberglass layer applied at the factory using high tech methods. Then, all we had to do was to bond this fiberglass layer to the other part, using thickened epoxy.

-I used a boat carpet kit from bass pro, including a couple bottles of latex adhesive and brown paper for cutting and fitting patterns. All fasteners are aluminum or stainless steel.

I shaved a few bucks off my costs by passing up marine plywood and, instead, built my decking with scrap 3/4 (nominal 5/8) inch exterior-grade plywood. It was fitted with ample clearance for carpet, sealed with fiberglass resin (two coats), and then bolted the decks down to aluminum angle bracing. Three pieces of plywood made a front deck that stretch from the center seat/livewell to the front, elevated deck. The center piece is bolted down, and the two side pieces are hinged to it with stainless steel boat hinges. Those hatches open with stainless steel, flush-mounted hatch rings.


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