Clark April 16th, 2015
A wise man once told me this, and I took it to heart.
While traditional enamels are still around, most modern boat paint is linear polyurethane (LP). Among LPs there are one-part products and two-part products. Two-part products cost a little more, but last longer. When you consider that 80-90% of any painting job is prepping, sanding, fairing, and masking, and this is all fairly onerous work, why use paint that won’t last as long?
Probably the best known two-part products are Awlgrip and Interlux’s Perfection. If you paint the topsides of your boat with one of these products it will look good for about ten years, give or take, depending on environmental conditions and crashing into things. One-part products, such as Interlux’s Brightside or Petit’s EasyPoxy, will apply like a dream and look great, but the gloss will fade after 3-5 years. Again, for the relatively minor price difference and the relatively easy step of measuring two liquids accurately and mixing them together, why not use the good stuff?
The rub is that you can’t put the good stuff over the cheap stuff. If you have ever painted your boat with a traditional enamel or a one-part LP product, then paint over it with a two-part product, the solvent in the two-part product will dissolve the previous coatings and make a disaster. Or will it?
From the the Interlux Perfection label:
“Can be applied directly over two-part catalyzed coatings, that are in good condition.” and “Do not apply over conventional paints or flexible constructions.”
The paint companies will tell you that you absolutely, positively cannot put a two-part product over a one-part product without first removing the former coating, down to the gelcoat. There is definitely some truth to this, and the paint companies should keep advising this, but you can get away with it.
I might add at this point that if your boat has never been painted – it’s still got its original gelcoat – DO NOT EVEN THINK about painting it with a one-part product. Slap yourself across the face, recalibrate your plans, and use a two-part product. Your boat will then be on its way to an lifetime of easily re-coating with additional two-part products, without ever having to worry about the substrate.
In my case my boat had been painted with one-part paint, all over, decks and hull. For the topsides I went to all the trouble of completely removing all the prior coatings, right down to the gelcoat. With advanced modern technology, the old coatings can be removed using a…two-inch paint scraper. That’s right, a paint scraper. There are some chemical removers, but most boat yards still go with a motivated worker with a scraper. This only takes like a thousand years. For the decks and superstructure it was just too much: all those curves and corners were not meant for a paint scraper.
I put two-part over one-part. There, I said it.
It’s like this: If you’ve got old one-part paint on your boat that’s been there a while, and it’s not peeling up, it can be considered a solid substrate. Sand and feather where it’s peeling, but everywhere it’s consistent and smooth, even if old and chalky, this can be considered a good enough for our purposes.
The two-part product, say Awlgrip, Perfection, or Petit EZ Poxy two-part, will have a two-part primer, usually an epoxy-based system that uses the same solvent as the top coat:
Once you’ve sanded, faired, and prepped your substrate, put on (brush, roll, or spray) your first coat of primer. Contrary to what they say, it will not peel up all the substrate. The substrate will peel up or crinkle here and there. If you are spraying an 85-foot hull in a high end boat yard, peeling and crinkling here and there is totally unacceptable, but if you’re painting the decks on your own boat and saving yourself hundreds of hours of heinous manual labor to remove the old coatings, you can live with a little peeling and crinkling.
Once dry, sand and fair the peeling and crinkling parts, which will usually be around the edges of the old coating, where the solvent can creep under it. Spot prep and re-coat the peeled and crinkled areas with the primer. Do this as many times as you need to, until you’ve got an even coat of primer with no peeling or crinkling, then put on additional coats of primer, per the manufacturers recommendations. Once you’ve achieved this, eureka, you’ve broken the rules and gotten away with it. You can consider your older, one-part coatings to be entombed forever. Go on with the process, sanding and fairing the the primer, and apply the two-part top coat.
It probably goes without saying that if you defy the advice of the manufacturers like this – it says not to do this, very clearly, right on the can – you can forget about any kind of warranty or support from the manufacturer. You’re on your own.
I painted the decks and superstructure on my boat, in this manner, about five years ago. Does it look as good as a professional, sprayed-on job, done in a boatyard? No, it doesn’t. I did it all with rollers and brushes and the results aren’t perfect, but pretty darn good. Where I went to extra effort, like around the cockpit, it’s pretty much perfect. Also, I used a flattening agent, to make the paint a little less glossy, and this is somewhat more forgiving:
For deck and superstructure a gloss finish can be blinding. Also, for the same reason, I went with an off-white. The topsides are full-on glossy white.
After five years a one-part product would already be showing its age and need to be recoated. My decks and superstructure have at least another five years of looking good, and when it comes time to repaint them, I can recoat with two-part products without starting from square one again.