painting gearcase

[SteveO]

The paint is peeling on the gearcase I painted last spring. What's the best method to paint one?
1) sand or sand blast, What grit?
2) Zinc Chromate primer - I probably used too much it. The Zinc is sticking, but the paint is peeling.
3) Do you use grey primer over the Zinc? What kind?
4) Sand the primer?
This gearcase spends the summer in fresh water.

[gaineso]

Does it stay in the water all the time?

Zinc Chromate is the right primer on aluminum. What kaind of paint did you put over it?

Personally, and I have it on my 'roundtoit list, i'd sand it down smooth and finish sand with 400 or 600 with all the scratches going straight ahead. Not if it stays in the water all the time though. Then you really want to protect it. Maybe add a couple of "Zincs" somewhere to protect against electrolysis.

Hope I helped a little.

[Delta]

It's tough to get paint to stick,especially if the paint is shiny/glossy.
My paint shop guy told me to apply the top coat over the zinc chromate while the zc is still fresh(about 15 minutes later...still wet/tacky).
Then do as gaineso says...wet sand it with 400.
It won't be shiny,but it will be faster and adhere longer.
Less friction is the key.
Good Luck,Delta

[CompKing]

I've had better luck using laquer over enamel seems to go on thinner and easyer to touch up.Found Zinc Chromate at my paint supply store in the normal greenish and also in light grey and dark grey.I use the dark grey so when it dose peal it dosen't show so much.On one I taped off a line below the cav plate and just dark grey primed it on the bottom and looked great for over 2 years.

[SteveO]

Yes, The boat sits in the water over the summer.

Zinc Chromate was tempo green. Paint was 'OMC'.
I had sanded w/ 220 grit prior to priming.

I'm wondering if I need to use something coarser to give it some grip. Then smooth it with auto grey primer?

I agree with the sanded surface below the waterline. I just knocked off the dust specs and took the shine off below the waterline with a fine scotchbright pad.

[longIsland]

you dojnt gotta sand all the old paint off, just the loose stuff, with like 100 paper, then work 150 to feather edge old paint to base metal, 180 to smooth then scuff with 220. now i prime, let dry, sand with 320 paper, posible touch up some defects not noticed before, prime again, final sand with 400 wet or dry, if you sand thru and pimer area to bare metal, spot prime and touch with the 400 before top coating, for a lower unit because of all the sharp angles the final sanding of the final primer can be done with a pad, one of them abresave 3M corp scuffing pads, they dont have sharp corners tjat can easy sand thru to bare metal. just have to knock primer down and scuff it up anyway

wet sanding lower units takes lots of time between steops for water to dry so you can spray, better to dry sand lower units so you can finish the job in one day

sand blasting removes metal along with old paint, i dont think is good, besides the rough surface would need lots of work to get it smooth for painting for a shine

if you sue too much primer, sand it thin, heat lamp or hair dryeer speeds up dry time, or hot sun

[Burke Kilgour]

If you want to go with the ultimate in adhesion, I'd bead blast it to bare metal, sand with 320, etch and alodine, epoxy prime, fill with epoxy as required (re-prime as necessary) and topcoat with alumi-grip.
-Alumi-prep 33 (etch)
-Alodine 1202
-U.S. Industrial paint epoxy primer (2 equal part primer)
-Filler- I like L&S's epoxy
-Alumi-grip ultra black
This whole proccess will STICK like you wouldn't believe !!!