Painting an outdrive

[Misfit Toy]

Hi,
I have a badly neglected Volvo Outdrive which I will dissasemble and sandblast all exterior surfaces. My question is regarding the paint process. Do I apply the factory paint over the primer and then use an antifouling or just skip the factory paint and go directly to the antifouling ? This is what most underwater antifoulings suggest. First you use their primer and the their antifouling over it. I think the factory paint followed by the anti fouling will give more protection and could possibly act as a signal coat once the antifouling wears away. Your thoughts on this are appreciated.
Thanks, Misfit.

[sinjun]

yes if you are going to use antifouling paint don't use the factory paint it will just be a waste of time and money. prime it antifoul it.

[mjkkemper]

below is something I found on another site

Painting Aluminum. It should be an oxymoron. But it happens. Especially aluminum out drives. I recently pulled my Mercruiser Bravo III. After 4 years of my paint job on it, not a single square inch of paint had eroded or peeled from the unit. Here is how I did it and some rules to remember when painting aluminum.

Number one. Aluminum will not take paint. Not bare aluminum, not etched aluminum? Surprised at “etched aluminum”? You see a lot of primers that say, “self etching”. Well etching is the process of using acids or bases to remove aluminum oxide and other contaminants. Where do the contaminants and oxides go in a “self etching” paint? That is correct, they are contained in the paint job. How long and how durable is a paint job with “self etching” paint after all those contaminants are contained therein?

Number two. Alodine will adhere tenaciously to aluminum and paint tenaciously to alodine. So alodine is our “negotiator” to paint aluminum. It provides the intermediary between paint and aluminum.

Surface prep. A lot of options here. If the paint job is original Mercruiser it comes off very easy because Mercruiser has a poor process. You can sand it off for the most part. If you want, you can get some “aircraft stripper” available at most automotive paint stores or Aircraft Spruce. The main difference here is the amount of ammonia in the stripper. What is critical in this process is to place several plastic bags over the input shaft and bearings and the prop shaft and carrier bearings and hold them in place with tape. If you have a nearby facility that does plastic bead blast paint removal, like an aircraft paint shop, they can clean off your drive as well. Just make sure to cover the pitot tube entrance on your drive. DO NOT SODA BLAST. You will make the etching process a very difficult one. Get the drive as best you can down to bare metal. DO NOT USE STEEL BRUSHES, STEEL WOOL, STAINLESS STELL BRUSHES, etc anywhere, any time. Always use aluminum oxide sandpaper and if you want a “brush” use Scotchbrite pad.

Etching. I use AlumnaPrep 33 available at Aircraft Spruce. You dilute it 1 part to 3 parts water. A quart bottle is more than enough for one drive. Follow the instructions on the bottle. USE RUBBER GLOVES. Brush the solution on generously. If you see a spot repel the solution it may have grease on it. Degrease it with acetone or MEK and put on more Alumnaprep. Leave the Alumanprep on at least 3 minutes then flush with fresh water. Use a hose. Flush like crazy. Your drive should have a dull but bright look to it after etching. Allow drive to air dry.

Alodine. Again available at Aircraft Spruce. Do not dilute. A quart will do a drive. Brush it on your dried, etched drive. Again, if you areas that are aluminum that repels the alodine, you go to de-grease. Clean and re-etch. Then alodine. Do not flush the alodine, allow it to air dry on. Your drive should have a nice “golden” tint to the bare metal.

Paint. Here is where you have some choices. I personally prefer two part epoxy polyurethanes. They are extremely durable, flexible (hard paints crack), and give an easy and very shiny finish that remains that way. The only negative is, any corrosion occurring beneath the paint surface will not be visible. The paint may bubble, but the coating will remain intact. Make sure you have sanded and etched away all previous corrosion before painting. I use Southern Polyurethanes. The other negative to polyurethane is you want a very good respirator and face shield when you paint. You can get one a Home Depot. Do not get the disposable kind. Get a 3M 4000 or 5000. Do not allow this stuff to get in your lungs. It does not come out, ever. Make sure your mask seals tightly around your face. If you have a beard, shave it.

Priming. I use Southern Polyurethanes Epoxy Primer. For a Mercruiser use black. Follow the instructions for mixing the hardener with the paint, (It is one to one). I use a small eight-ounce touch up gun. It just about covers a drive. First spray a flash coat, and then come back with a wet coat. After this when the wet coat is highly tacky and not subject to running, come back again with a full second coat. If you feel rich and want to burn some paint put on a third.

Zinc-Chromate Primer. A lot of people swear by this stuff. It is very good coating on etched aluminum, but not under water! It contains zinc! Think about that for a moment? There is one place to use zinc-chromate. On your bearing carrier after repainting the drive.

Color Coat. I use Southern Polyurethanes Universal Black, 4000 series. Again just like the primer, activate it one to one. Spray a flash coat then a wet coat. I do two applications. You’ll like this step because you’ll be amazed at how bright and shiny your drive is.

Clear Coat. You can (optional) clear coat your drive with Southern Polyurethanes Clear 4000 series. Do it just like the color coat. You can buff it if you want. Alternatively you can put on clear anti-fouling. You have to be prepared that clear anti fouling will “degloss” your finish and after a few weeks in the water, it looks like your drive is “cloudy”. Your underlying polyurethane finish is intact and is fine.


Refinishing. As I said, I recently removed my drive and the paint was intact, but I wanted to “clean her up”. I removed the clear anti fouling with #60 sandpaper. I roughed up the polyurethane finish coat with #60. In the process, I broke through to bare metal in a couple of spots. No problem. Etch those spots with AlumnaPrep, then alodine them. I sprayed two coats of Epoxy Primer, two Coats of 4000 black, then two Coats of Clear. Here are the results. Note the sheen near the bottom of the drive.

[cheapboxer]

I did mine last year by the book with Volvo primer and paint and late in the season I had more crap hanging off them than ever before and needed to power wash them.

After talking to the people from Interlux it appears one additional step should have been done and by not doing this it probably caused the Volvo paint (and any) to fail. They think someone could have waxed my outdrives at some point and when I sanded them I was actually pushing some of the wax deeper into the existing paint or aluminum. Interlux Trilux 33 is the paint they have developed for outdrives.
In there process you wash the drive with a wax stripper before any sanding is done. Then sand and use the stripper again just in case there is any wax remaining. 3-4 coats of primer and 3-4 coats of Trilux 33. They don't have the Volvo gray color so I used the black.

BTW Only use aluminum oxide sandpaper. I would think the same for sandblast media.

[Rob Pirie]

I would definitely prime and 2 pak paint prior to antifouling. You need to give your outdrive as much protection as it can get , antifouls on aluminium parts these days can let growth start in weeks and once you scrap it off your back to bare metal , you need that extra protection.

If you know you're not going to use your boat for a few weeks/months just slip a plastic trash can liner over your outdrive and drop in a small amount of chlorine , nothing will grow in that.

If your boat is connected to shore power you should have a Galvonic Isolator fitted . Whenever a boat is connected to shore power, the hull and drive system is connected to the shore grounding system and to other adjacent vessels (also connected to shore power) via the grounding conductor in the shore power cable. This connection, while required for safety, creates a galvanic corrosion cell involving the dissimilar metals between boats and between a boat and the shore grounding system:- this explains it a bit better ://www.marinedirect.com.au/catalogue/c2000/product57929 http://www.boatersworld.com/product/196902548.htm

Hope this helps.

Rob

[jobowker]

You absolutely need regular paint on it!! You can follow the detailed instructions above - it sounds pretty thorough and mjkemper makes a number of valid points. Alternatively, you can sand it, clean it, and then quickly prime it before it oxidizes. Let the primer dry for the time specified on the can, then color coats, then clear coat or antifoul.

For those who think that you shouldn't have to paint aluminum, the reason you generally don't have to paint it and it doesn't seem to corrode is not because it doens't corrode - it's because it QUICKLY oxidizes on the surface forming a film, and that film prevents oxygen from gettign through to the rest of the aluminum. If you need paint (and in this case, you do), the primer sticks tenaciously to aluminum, but not as well to aluminum oxide. That's why after you get it all cleaned up, it needs a final snading and cleaning shortly before the primer goes on.