Pitting on transom!

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Apex Predator

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The previous owner of my Monark 1644 left the battery connected on the electric start motor. The outside of the transom has some pretty bad pitting on the exterior. What is the best way to permanently repair this. I was thinking sandblasting, kill oxidation with Ospho (or similar), and filling the pitted area. What to treat the aluminum with? What to fill the holes with? Bondo, Devcon, 3M 5200? Thanks!
 
Hi apex. Sorry to hear about the pitting. Unfortunately, none of the products you listed will work for this particular job. The best material to use to fill in the pitting is probably going to be JB Weld and/or Marine Tex. The good news is that you can get JB almost anywhere, including Lowes/HD. It comes in a runny, 2-part, black and white form that you mix in equal parts just prior to use. It's great for filling small pin holes and/or spreading around to fill in the pitting. There is also a JB Marie epoxy putty. It's sort of has the consistency of Play-doh. You knead it just prior to use and it's great for filling in larger holes and/or seams. Once it fully cures, JB can be sanded primed, painted, or machined. I would probably apply several skim coats of JB, letting each layer cure fully in between applications. After it was done, sand it smooth, wipe down with Acetone and prime with aerosol, Zinc Chormate Self-Etching Primer. You can get it at most auto parts stores, Wal-mart, Lowes/HD, etc... You only need a light dusting. Then apply the paint of your choice. Rutoleum Professional aerosol is nice, but there are many brands. Be sure you never put in pressure treated wood in the boat either, or you'll get more pitting. Instead, use non-PT, exterior grade plywood and seal it with epoxy, fiberglass mat & resin, or several coats of spar urethane. Then secure all wood to the boat using Stainless Steel hardware dipped in a bit of 3M 5200.
 
Apex Predator said:
I appreciate the response! Any prep before filling the pitting?

You've got to get the corrosion out first. Zepalume or Alumabrite would be a good choice if using acid, or if the pitting is mostly on the surface, it can be removed mechanically, with a 3M scotchbrite (TM) or equivalent.

The important thing will be to get rid of all of the white, chalky oxidation. You are going to have to get down to clean metal everywhere.
 
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