[bherron]

I was planning on painting the aluminum siding on my pontoon boat, but have a couple questions. Do you have to spray with primer first? Will "auto" paint work fine?

[stevieray]

If you have any bare metal showing, best to hit those spots with a zinc chromate primer. If you're going right over the factory baked -on paint, you can just clean off any dirt & chalky oxidation & spray the finish right over that. If it's been painted with any air-dry paint already, test a small area for compatibilty - auto paint may "lift" some air-dry enamels.

[Bond-o]

Do you have to spray with primer first? Will "auto" paint work fine?

Like Steve says,.......
As long as the Paint that's there is in Good shape,......
A Good Cleaning,+ Scuffing it Up abit will be Fine.......

Other than on a Bare Metal situation,.....
Primer is More for leveling repaired areas,+ to give the Top Coat a nice clear neutral Base,....
To Hide Stripes or Repairs......

And,..........
I use a 2pt. Ureathane Automotive Paint to paint about Everything nowadays,........
Above,+ Below the Waterline....... No Issues,.. No Problems.........
The stuff is Harder than Nails,....