We had this rusty keel problem last year with our Maramu. Some rust along the joint of the steel keel.
We had work done at Nanny Cay on Tortola while we were not present. I It looked great when they were done but I found out later they just blasted the entire area, removing the epoxy to bare metal. They let it sit overnight. They applied Micron 66 onto the metal. A truly shoddy job. We had pervasive rust showing within two days of launch. Lesson: Either do the work yourself or supervise closely.
After 3 weeks in the Virgin Islands we sailed to Fajardo and hauled out at Puerto del Rey. We let it dry for 5 months, then traveled to PR from Washington State and moved the boat from land storage to Island Marine Inc. boatyard. (They were highly recommended by another Amel owner.) I discussed the work with the manager (Ken) and told him to fix it right while we stayed in a condo nearby. I trusted Ken but I supervised daily to prevent a repeat of the Tortola experience. I had some directions and advice from Dave Benjamin (who helped us find and buy the boat) from his experience with his 1979 Maramu. He was kind enough to send me a copy of his log entries from when he had similar work done.
The keel was blasted with low pressure, high volume water and sand to remove all previous coatings on the steel. That took most of one day. That was allowed to dry and the steel was sanded, and polished and immediately (within minutes) coated with rust lock. That was allowed to dry overnight and then sanded and polished again and three more coats of Rust Lock applied. That was allowed to dry overnight, then three coats of Interlux 2000 epoxy were applied. Then more sanding and all the various pits were filled. That was allowed to dry and then three more coats of Rust Lock. That was allowed to dry then three more coats of Interlux. After drying, two coats of Micron 66. Basically, six coats of rust lock, six coats of epoxy, and two coats of Micron.
The bottom of the keel was mostly accessible during the process so the same procedure applied there. At the end, we put the boat in the crawler and finished doing the spots on the bottom that were inaccessible. She sat in the crawler for about 7 hours while multilple coats of Rust Lock and Epoxy were applied. That was the only part of the process that I wonder about but the two areas on the bottom of the keel that were inaccessible were very small.
The most important part of the process is to expose the bare metal and IMMEDIATELY (WITHIN MINUTES) apply the first barrier coat. The oxidation starts right away. Its best to have two people working so the first barrier coat goes on right away. If the metal sits exposed it should be sanded and polished clean before the first rust lock is applied.
This whole thing cost us just less than $1,500 and 1/3rd of that was for materials. I believe we will not see rust again for a long time. Plus, the keel surface looks great. Much smoother and the pits are mostly gone.
I think this is a job worth doing right. Between Ken and I, the job was supervised constantly. If possible, this is a job you can do yourself but I am glad we paid Island Marine to do the work.
The good news regarding Nanny Cay is that we discovered the crappy, defective work done there before I paid their invoice.
I will try and upload some photos of the work we had done.