Are primer coats necessary?

[TooCoys]

I'm currently planning and budgeting a DIY paint job on my boat. I will be taking three weeks of vacation in January and starting with a bottom job. If I have enough time I'll move to the hull, and after that if I still have enough time I'll be painting the decks and hard tops.

The boat is 51 years old and I know that at least the hard tops have previously been painted. The rest is very oxidized, original gel coat with some unkept polyglow coating on it.

I plan to use all one part Interlux paints, but my question is - are primer coats necessary?

I'm not looking for extremely professional results, I'm just looking to cover the boat and protect it, and increase its visual appeal somewhat. Can I get away with only priming any blisters or gel coat repairs that I may have to do?

[mikedefieslife]

I don't know about your particular paint. I presume it is a polyurethene though. Normally, you don't need a primer for going over gel coat, but best check the data sheet.

The gel coat will need a thorough clean with something like oxalic acid. You will also want to abrade it, and then clean again with acetone or similar.

This is my experience with International paints, like Interdeck. Your paint may be different.

[GordMay]

I don’t believe “primer” is explicitly required, but they recommend:
Brushing Liquid 333 To ease application
Special Thinner 216 For wiping down previously painted surfaces or spray application
Fiberglass Solvent Wash 202 To clean bare fiberglass prior to application


PREPARATION

Previously painted surfaces in good condition
Remove surface contamination by wiping down with Interlux Brushing Liquid 333 or Special Thinner 216. Abrade with 220-320-grit sandpaper.

Previously painted surfaces in poor condition
All previous coatings should be removed and the substrate primed.

Priming
All preparation for bare substrates is covered on the appropriate primer label.

Fiberglass
No priming necessary but clean as above and abrade with 220-grit sandpaper. If surface is cracked or crazed, use Pre-Kote.

See ➥ http://www.yachtpaint.com/Literature...fo-usa-eng.pdf