Non-marine paint for down & dirty dinghy

[bcripps]

Using industrial epoxy to build a cheap plywood dinghy in a remote location... no marine paints available. What's my best bet for paint over cured and sanded epoxy. I hear an acrylic latex offers good UV protection, but what about something like concrete porch paint? Or something similar to Rust-oleum? Priority is paint that sticks (primer?), not a high end finish.
Thanx everyone,
Bry
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[Jammer]

There is a hierarchy.

At the top, two-pack paints, available from industrial and auto body sources.

Closely related, there are some high quality auto body and industrial one-part paints with an optional hardener, that are also very good. They are better with the hardener, of course, but it's expensive and toxic. Generally the active ingredient in the hardener, as in two-pack paints, is an isocyanate.

Next, one-part urethane paints, like porch/garage floor paint. Color selection tends to be limited. They can be tinted though not all paint dealers are knowledgeable enough to do it. These are much less expensive products, and less toxic. They are more difficult to apply to a high standard of evenness and gloss, require more drying time, and are not as durable, but do provide acceptable results if you are willing to work with them.

Subsequently, exterior alkyd enamel paints, like retail Rust-oleum etc. These lack durability compared to the urethane fortified products.

Then exterior latex.

[Jammer]

I would not recommend the cement paints. The ones I've used do actually contain portland cement. That's fine on a cinder block foundation but you don't want it on a dinghy where the extra weight will be problematic.

[pcmm]

Rustoleum IS great paint and lasts longer than you expect in the sun. Or find "farm implement paint" very hardy paint and both are vefry inexpensive. I used Rustoleum to paint my forest green stripe on my morgan and that paint is now 6 years old. cost me $16 for the can and I rolled it on. did a good enough job.

[garyfdl]

Back in the mid '70's I had a friend who had a 49' wooden schooner. I helped him (and learned) a lot with working on the boat. As the guy was a 30-something electrical engineer, and not made of money, he looked for viable alternatives to labeled 'marine products'.

For paint? We used high quality oil based house paint (above the waterline). At the time, Sears paint was very good. We also used high quality exterior caulk (again, above the waterline).

My only question would be if house paint would stick to an epoxy surface.

You might try contacting Paul Oman, the proprietor of Epoxy Products for advice. The guy is a small operation but is a wealth of knowledge,

https://epoxyproducts.com/

[Kijit]

We started using latex house paint several years ago for the topsides on a 112 year old museum sailing vessel that I used to captain. We found it held up at least as good as "marine" topside paint and cost a whole lot less!

[Chotu]

Originally Posted by garyfdl

Back in the mid '70's I had a friend who had a 49' wooden schooner. I helped him (and learned) a lot with working on the boat. As the guy was a 30-something electrical engineer, and not made of money, he looked for viable alternatives to labeled 'marine products'.

For paint? We used high quality oil based house paint (above the waterline). At the time, Sears paint was very good. We also used high quality exterior caulk (again, above the waterline).

My only question would be if house paint would stick to an epoxy surface.

You might try contacting Paul Oman, the proprietor of Epoxy Products for advice. The guy is a small operation but is a wealth of knowledge,

https://epoxyproducts.com/

Exterior latex house paint from Home Depot sticks like crazy to epoxy. With no primer!

In 2014, nearly 10 years ago now, I had a friend who had never touched a paint brush or a paint roller in her life paint my dagger boards with some exterior latex paint just to keep the sun off them. It was a temporary thing to get done very quickly.

she slathered on that exterior latex Home Depot white paint Tom Sawyer style with a brush. It’s all patchy. It doesn’t look right. Not a good paint job, because she didn't know how to put in on evenly. Ha ha that’s OK it was supposed to be sanded down and re-painted anyway. The paint would only last a few months, right? Especially on epoxy with no primer, right?

well here we are, almost 10 years into the future now, and the paint looks the same as it did the day she put it on!

it’s perfect. (But her paint job is still terrible. Haha)

I do have a question about rustoleum because I thought it sticks even better than the exterior latex paint. Can you expand upon your post a little bit more, jammer? I’m curious. Because I painted some metal with rust oleum and it’s working out great years into the future as well now.

I don’t know why it ended up so low on the hierarchy.

and finally, I don’t think we all (collectively) know what we’re talking about when it comes to paint. We are just suckers for the marine industry marketing. I’m sorry to bring everyone down, but it’s true. All of the paint works. And it all works over whatever substrate. And you don’t even need a primer usually. It’s crazy, but these things you read online really aren’t true. Maybe paints have changed over the years and people are stuck in the old days or something. But all of the new paint just sticks. For that matter, Bondo sticks. And that has a really bad reputation as well.

I tried a small test patch of Bondo inside the boat to see about smoothing out the interior for paint. Well, I can’t get it back off! I can’t peel it off. I can’t chip it off. It just won’t come off. I can’t scrape it off. There’s no way to get it back off. It has been sanded flush and that’s the best I can do. and it was put on unsanded, shiny epoxy with no primer, no tie coat, nothing else. Just slathered right on there. Just to see how it would work for smoothing the interior weave.

sometimes it surprises me when I try a little test patch of something that I’m not supposed to. And it works just as well or better than the marine stuff.

i’d say the only difference between some off-the-shelf paint and marine paint is that sometimes the marine paint is harder. It can resist scratches easier. It doesn’t stick any more or less. It stays on.

and it’s the same for automotive linear two-part polyurethane paint. There is absolutely no difference between that and the linear 2-part polyurethane marine paint. Look at your car hood. The side of your car. Does it deteriorate over time? No. Is it easy to scratch off? No. It’s exactly the same. It’s the same paint.

[Benz]

The reason for primer is not so much so that topcoat will stick, since as it's been pointed out, paint is sticky stuff. It's so that the surface being painted on has a consistent texture and hue, so that the topcoat comes out perfectly even. It just helps the topcoat do its job without a lot of extra coats.

[Chotu]

Originally Posted by Benz

The reason for primer is not so much so that topcoat will stick, since as it's been pointed out, paint is sticky stuff. It's so that the surface being painted on has a consistent texture and hue, so that the topcoat comes out perfectly even. It just helps the topcoat do its job without a lot of extra coats.

Ha! All these years I thought the primer was mostly for adhesion purposes. Live and learn

[Jammer]

Originally Posted by Chotu

I do have a question about rustoleum because I thought it sticks even better than the exterior latex paint. Can you expand upon your post a little bit more, jammer?

Well, two parts to the answer. First part, I see the alkyd enamels as a group having better overall performance than exterior latex, so I think we're in vehement agreement about that part.


Any paint will adhere to properly prepared and abraded epoxy, or fiberglass. Or wood that stays dry. Getting paint to adhere to, say, aluminum, or unprepared steel, or glossy paint that hasn't been sanded, is more difficult. On these surfaces, either a high-performance paint or an adhesion-promoting primer are necessary to get good results. Or you can sand. Steel is somewhere in between because latex paints will typically allow steel to rust under the paint, leading to an adhesion failure, although there are latex paint systems now that have corrosion inhibitors.


Another aspect of adhesion is flexibility. Paints that are flexible can stay adhered to substrates that flex, while paints that are hard will not. This matters with things like wood that swells or components like cables. Latex paints are inherently flexible. Alkyd and urethane coatings can be, or not, depending on how they are formulated.


Second part, there is more to paint than adhesion. Sure, paint has to adhere, but there are all kinds of other important properties, like abrasion resistance, sunlight resistance, mildew resistance, appearance, ease of application, number of coats required, color retention, color availability, etc.


Latex exterior house paint is typically formulated to chalk. That is, with exposure to weather, the outer layer of pigment and binder will wash away, so that unweathered paint becomes the new exterior surface.

[Jammer]

Originally Posted by Benz

The reason for primer is not so much so that topcoat will stick, since as it's been pointed out, paint is sticky stuff. It's so that the surface being painted on has a consistent texture and hue, so that the topcoat comes out perfectly even. It just helps the topcoat do its job without a lot of extra coats.

I think this is true on typical well-prepared surfaces. Primer is cheaper than premium topcoat products, and also usually easier to sand, so it's more money and more work to switch from primer to topcoat too soon or to skip primer altogether.


On difficult surfaces, e.g. aluminum, primer does have a role in promoting adhesion.

[capt jgw]

We used exterior latex gloss house paint on one of the commercial boats I ran. Held up pretty well and stayed shiny several years. And of course was cheap. That boat ran on cheap.
I did the interior of my own boat with the same stuff and was quite happy with it. Downside to it is you can't get a mirror finish with it like you can with enamel. It doesn't flow out as well. Sounds like the OP doesn't really care about that though.
Rust-Oleum is probably about the same cost but can give a better finish if that's important. I've used that on fiberglass. Doesn't hold up as well as high cost marine paint but is fine for quick & dirty.

[bcripps]

Thank you, everyone. Some amazing information and I appreciate everyone's time and knowledge. For me, marine paint is simply not available. But there is a hardware with an automotive section so I'll start there and see what's available. The suggestion of farm equipment paint was duly noted.
Next I'll see about an outdoor acrylic. Luckily it's a small dinghy and will be quick to sand and re-paint in a couple of years, if needed.
Much thanks,
Bry
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