Painting the underside of your aluminum decks

Ok...Show of hands how many of y'all have taken measures to protect the underside of your aluminum decks when used in salt water?

I'm wondering if I can get away with just priming the underside to prevent the I'll effects of saltwater. Or, should I prime and paint the underside. Obviously the primer won't be exposed to the sun so that won't be a problem.

the paint college I went to a long long time ago discussed this very topic.
primers have ingredients in them such as acids, salts and inert material
that actually attract moisture. that is why you see so many rusty
repairs on vehicles with primer gone bad - the general perception
is that we think the primer will protect bare metal until it is painted - but it won't.
primers are designed to make a physical bond between the metal
and the top coat - the top coat is what provides the protection - not the primer.
there are some exceptions to the rule - such as industrial primers that contain sealers.

so - in my personal opinion, if you want to prevent oxidation - prime AND paint.




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UPDATE: I removed the deck lid from my '59 Crestliner
and under the deck was a powdery oxidation.....
since it was off, I wanted to paint it. A member here (sorry, I forgot who)
suggested Easy Off oven cleaner to remove the oxidation.
wow - this simple process WORKS !!
I let the cleaner sit for about 5 minutes and scrubbed with a brush
then rinsed with clean water and it is ready for primer and paint.
of course this process will kill every type of vegetation it touches.
so you must find an area that you will be content with dead grass until next year.




the dark areas is surface corrosion in the beginning stages.
I will give it the Ospho treatment prior to acid etch primer and paint.

not bad for a 58 year old boat that has seen its share of salt water !!
hopefully, I can make it last another 58 years.



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Nicely done! I took your advice and primed/painted every surface where there would be metal to.metal contact. That way if saltwater DID ever find its way between the pieces, it wouldn't be as big of a deal.

I coated the top side of all the stringers and supports with Tuff Coat for added protection, and sound deadening. I don't know about anyone else, but when the engine is idling I used to get tiny vibrations from anything​ that wasn't​ riveted down tight.