Rust - Your thoughts

[peptobysmol]

I understand the most appropriate way to fix a iron keel is to scrape/sandblast/grind to bare metal then treat it. However, I'm wondering if this product (Blackstar Rust Converter) is adequate. I'm looking for a quick fix. I'm also looking for one that is a prudent fix. Has anyone had any experience in treating an iron keel in such a manner? The product says its guaranteed...

Thanks, Brad

 

[RichB]

Pepto,
Good to read ya. I don't know 'Blackstar' ... but I think all rust converters are a superficial temporary fix. I redid my bottom (and keel) last winter and had to grind some wet cast iron off the keel. SO.... grind away ALL rusted iron. Immediately slap some phosphoric acid on the bare spots. Wait a while then do the filler with thickened epoxy. (I used PC-7 in the cans) ((don't even think of using polyester/Bondo)) Come back the next morning and grind/sand smooth and paint several coats of 2 part epoxy. Now it is ready for bottom paint.

Down here in salt water the more epoxy barrier the better. I was also able to get to the bottom of the wings and keel because I took it off the trailer in my driveway and used 4x4 blocks and 2 floor jacks to jockey the blocks. It looked fairly precarious hanging under a homemade 2 x 10 wood frame with truckers ratchet straps. The neighbors pronounced me crazy but not one guy volunteered to lay on the mechanics dolly with a sander at arms length.

 

[Jalepeno]

I bought an 86 h23 in 97. She had a lot of keel rust I had it cleaned with a flexible disk grinder and then had the yard put four coats of epoxy barrier paint, faired the transition to the hull and one thick coat of CSC bottom paint. Never rusted again in the ten years I had here.

 

[MrUnix]

I was unable to find the MSDS sheet for the Blackstar product, but it looks like nothing more than phosphoric or tannic acid under their own 'trade name' (both will convert rust into a black inert coating suitable for painting).

Cheers,
Brad

 

[kendall]

May not apply to constant immersion, but my experience with rust-converters on motorcycle exhaust has been very favorable.
On my old Honda, it was an annual spring event to remove, clean, sand, and paint the exhaust. Always used high temp ceramic paint, and generally it was looking old by mid summer. One spring I decided to try phosphoric acid on it, so I sanded it completely to bare metal, let it 'flash' rust and sprayed it with the converter, let it dry and then used the normal ceramic hi temp on it.
Over the next 5 years,(sold it) all I had to do for my spring routine was to touch up a few small stone chips, and hose it down to have it look like new.

Like I said, different application, but motorcycle exhaust is a very hostile environment, so I would be willing to try it on an iron keel.

 

[RichB]

Phosphoric acid aye....... Good to know what the active ingredient is in 'rust converter. I love the stuff for tools I keep on the boat and lots of other stuff. Florida is a very rusty place and I keep 2 or 3 spray cans on hand. (Dupli-Color brand from Discount/Advance Auto Parts)

 

[RichB]

Final answer ....... I find that rust converter only works on surface rust. Using it on my trailer with the scaley rust chipped off, it doesn't turn black even after several coats.