The Dreaded Keel Joint

Last post I talked about refinishing my iron keel and the wonders of POR-15. At haulout my keel looked like it had done fine under the water; no signs of rust. This spring I found a line of oxidation along the keel joint, which you can see in the pictures.

Rust along the hull-keel joint.

This is likely due to the fact that I filled and faired the keel joint with fairing compound instead of a flexible poylyurethane bonding sealant. The fairing compound is totally stiff and showed signs of cracking in a few places. I scraped and sanded away the oxidation stains and antifouling paint. In a couple of spots I hit bare metal, so I knew I'd be off to the store for some more POR-15 and Interprotect 2000 to make a few touch-ups. VC-17 antifouling paint turns black within a few weeks, so sanding it off along the joint allowed me to inspect the situation more closely.

The hull-keel joint sanded

Things looked pretty good at this point and I was second-guessing my decision to do any major work on the joint. A couple of spots had cracked or missing fairing compound, and had allowed water seepage. I toyed with the idea of simply scraping and patching these spots. Initially I used a simple triangular can-opener, sharpened on a grinder, to scrape at the fairing compound in the joint. This removed a few small pieces of compound that hadn't bonded well or had rusted underneath, but in general it wasn't very effective.

The alternative was to use a dremel tool, but I was pretty reluctant to try this at first since I thought I might damage the gel-coat and fiberglass on the hull itself. Apparently the flange on the keel is about 5/16" high (that's the part that extends inside the hull) and by staying up against the flange, and using the dremel tool no deeper than that, cleaning out the joint with a small burr is alright. I donned my mask and goggles, bit the bullet and fired up the dremel tool. The result (of the port side) is seen below.

Keel joint after dremel tooling

The port side went pretty smoothly but the keel butts against the hull on the starboard side, making things more difficult. Once this joint is cleaned a bit more, perhaps with a bit more hand sanding ro remove fairing compound from the edges, I'll treat the keel side of the joint with Metal-Ready, POR-15, Interprotect 2000E.

After that I'll tape the hull and apply either 3M 4200 or Sikaflex 291 (essentially the same) into the joint, smooth it out. These are rapid-cure caulks and should be ready in 2-3 days for painting over with Interprotect 2000. Finally, VC-17 will go over the entire underwater surface.

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