Proper painting of hull

[hoohaah]

I have measles on 30% of our 39' hull, I scraped off some of the bumps & saw bright aluminum underneath. I expected to see some type of paint or primer, do I need to strip the whole hull or only the areas of bumps. It seems the paint did not stick to the hull. The boat is inside heated storage & not sure if the work can be done or does the boat have to be out side to do the work.
Any suggestions to how to proceed would be helpful. I don,t think my marina has had much experience with Aluminum hulls. I keep her at Tower marine in Saugatuck MI Thanks for your replay Wally & Kris oh Hoohaah Too!

[bcassedy]

I would suggest spot checking some other location on the bottom (sand and/or scrape) to see if your boat's bottom paint consists of primer and then bottom coat. The "measles" areas could be where there was a touch up done but not done correctly. A spot check would verify. If spot check(s) show good paint, then you could just manually sand down the "measles" areas, prime and final paint. (You should prime the spot check(s) locations quickly to avoid the just sanded aluminum from oxidizing.
If the spot test shows there's a faulty paint job in place, stripping the bottom down to bare metal will be called for. This requires sand blasting and inside a storage facility may be problematic (other boats in area?), followed by a proper priming (with fairing applied/sanded smooth to pitted areas, if any noted), after the 1st primer coat) and bottom paint process.

Bill

[hoohaah]

Thanks for the follow up, I will check more areas for loose paint. This site is great for learning how to perform proper maintenance to your Marinette
HOOHAAHTOO

[hoohaah]

After speaking with the service manager at Tower Marine, further inspection of the hull, this spring we will strip the bottom & repaint the bottom complete. They have a great paint guy there & they know about etching the hull as soon as its stripped. If I can figure out how to download pictures to this site I will try to post before & after pictures.
Wally

[jralbert]

Assume you will sand (or glass bead) blast the bottom. I did and got very good results. got the first etch/primer coat on as soon as the sandblast crew finished and once that was done, could relax til the rest of the coats were applied. I got a 5 mph jump in speed after repainting (though your mileasge may vary). It was nearly baby bottom smooth. Be sure to cover bottom electronic and thru hulls so blasting material doesn't damage or intrude. I used a pie plate over the capac and double layer of tape over thru hulls, sonar, speed paddle, etc.

good luck with the project.

[Fastjeff]

The thing to remember here above all else is that aluminum corrodes almost instantly when exposed to air. The result is a slippery coating of aluminum oxide that paint will NOT adhere to. The etching process removes that coating, replacing it with something paint adheres to (usually aluminum phosphate). Those who have ignored this simple fact have had paint falling off in short order--and that includes boatyards who should have known better.

Jeff

PS: If you want to see a fascinating demonstration of this instant corrosion process, try using the Gudgeon Brothers Method on some scrap aluminum. Sand it to bare metal, then "wet sand" it with some coarse sandpaper dipping in CLEAR epoxy. The clear epoxy with turn silvery in short order--that's the oxide coating being forcibly removed.

[Maestro]

If you have areas of aluminum that are pitted, PC-11 epoxy has been recommended by others on this forum. After the first coat of primer, fill the pits with PC-11.

I had my hull hydro-blasted a couple years ago and found some very minor pitting. I filled with the PC-11 and it seems to have held up very well.

I used Interlux Interprotect 2000e for primer. It has also held up extremely well. I was not as thrilled with the Interlux Micron CF I used for antifouling. Switched to Jamestown Total Boat Copper free and was not happy with this paint either. I am due for a touch-up this spring and I am still contemplating which paint to use...

[Fastjeff]

Trilux 33.

Jeff