Epoxy (floor) paint for a boat?

[laukejas]

Hi,

I am at the stage of building my new 4.5m sailing dinghy when I need to decide on the kind of paint I'll be using. The build is 3D printed core carbon fiber composite sandwich, so I'll be painting over peel ply finish, unless I mess up resin infusion and fairing will be required. So basically painting over roughed up epoxy, with or without primer as needed.

Now, in the past, I tried acrylic, enamel, polyurethane (single and two part), various kinds of indoor and outdoor paints, but none of them impressed with their durability and scratch resistance. For this boat, I want absolutely the most durable paint there is so that I don't have to lay a carpet for her every time I need to launch and recover from sand/gravel shores.

I know some guys swear by car paint. As I understand that is acrylic enamel base and polyurethane topcoat. However, I don't have spray equipment, I want to do roll and tip, hopefully well enough to get a mirror, orange peel free finish so that I can skip sanding and polishing. As I understand, car paint isn't well suited for roll and tip. Correct me if I'm wrong.

Now, it came to my attention that there is such a thing as epoxy paint, typically used for garage/factory floors and other surfaces that demand extreme durability. It is reasonably cheap where I live (about the same as 2K polyurethane, 50$ per gallon), so I'm considering if perhaps this is a better option? Unfortunately I can't find much info on it's use on boats, hence this post.

Since price isn't a problem, can anyone comment if epoxy paint would be a better option over the alternatives? If anyone tried it, how well does it level out, how many and how thick coats I should plan for? Does it form orange peel? If sanding and polishing is required to get a mirror finish, how much effort should I expect? What about flexibility, should I use it on spars as well?

 

[ondarvr]

Epoxy floor coatings weather terribly, so it would look good short term even if you achieved the desired finish to start with.

Should be easy to find an indestructible coating that yields a showroom finish right out of the can at a rock bottom price though.

 

[wet feet]

None of them will withstand being sat on a gravel surface.If your hull is rigid enough,the most suitable would be 2 part polyurethane and you need a padded launching trolley to keep the boat on.The car paint equivalent would work if you had a good booth and a spray system,it also obliges the painter to use an air fed mask to avoid serious health problems from the fumes.It won't work with brushes and rollers at all well as it is formulated for a more rapid cure than would be achieved with manual application.I would expect an epoxy paint to crack due to it's inherent rigidity,floors are pretty rigid normally.

 

[laukejas]

None of them will withstand being sat on a gravel surface.If your hull is rigid enough,the most suitable would be 2 part polyurethane and you need a padded launching trolley to keep the boat on.The car paint equivalent would work if you had a good booth and a spray system,it also obliges the painter to use an air fed mask to avoid serious health problems from the fumes.It won't work with brushes and rollers at all well as it is formulated for a more rapid cure than would be achieved with manual application.I would expect an epoxy paint to crack due to it's inherent rigidity,floors are pretty rigid normally.

Thanks for your comment. I wonder though, what kind of paint do commercial composite dinghy manufacturers use? Like Laser, RS boats, Optimists, etc. In my local regattas, I've seen plenty of these boats being abused, dragged on sand, gravel and even rocks, without any padding, any trolleys, and yet when I inspected the bottoms of these boats, I could hardly see any scratching at all. They do seem indestructible. Is that gelcoat/topcoat instead of paint? Maybe I should use that instead? Or do they typically use something else to achieve such hard finishes?

 

[wet feet]

The commercial dinghy builder would naturally use gelcoat,it is just commercial reality.They don't want to lose the time and increase the cost of the boat by having to apply a coating.Which is why their boats are female moulded with a gelcoat as the first thing to be applied to a mould.A hobbyist can't normally justify the time and effort of building the well finished mould that forms the first part of the process.Applying gelcoat and having to abrade and polish to a high level of finish is really laborious and you would need to find a product which could be depended on to adhere to your laminate.

 

[laukejas]

The commercial dinghy builder would naturally use gelcoat,it is just commercial reality.They don't want to lose the time and increase the cost of the boat by having to apply a coating.Which is why their boats are female moulded with a gelcoat as the first thing to be applied to a mould.A hobbyist can't normally justify the time and effort of building the well finished mould that forms the first part of the process.Applying gelcoat and having to abrade and polish to a high level of finish is really laborious and you would need to find a product which could be depended on to adhere to your laminate.

Understood. I have had to sand and polish some gelcoat in the distant past, and I do remember it being an awful job. But in general, is gelcoat harder and more abrasion resistant than even the best paint that home boat builder can use? Is that why these factory boats are so indestructible?

 

[wet feet]

A lot of time and money has been invested in the development of durable gelcoats,so you would expect it to have produced a product that works well.You would need to find a chemist to advise on the mixtures of plasticisers and other modifiers that may have been added to the basic monomer.Your observations have provided the evidence that the process has yielded benefits.Do keep in mind that the whole manufacturing process will have been refined and the whole laminate adjusted to produce a good boat with reliability and a chance of profits.It is a bit ambitious to expect to match such boats with less of a boatbuilding background.After a few boats it isn't so much of a hurdle.

 

[skaraborgcraft]

Compare gelcoat thickness to that of car paint. That is why even deep scratches "look fine" as its just thick pigmented resin. You could add copper powder, graphite is popular on bottoms, but really, they can all scratch given the right stone.

 

[laukejas]

A lot of time and money has been invested in the development of durable gelcoats,so you would expect it to have produced a product that works well.You would need to find a chemist to advise on the mixtures of plasticisers and other modifiers that may have been added to the basic monomer.Your observations have provided the evidence that the process has yielded benefits.Do keep in mind that the whole manufacturing process will have been refined and the whole laminate adjusted to produce a good boat with reliability and a chance of profits.It is a bit ambitious to expect to match such boats with less of a boatbuilding background.After a few boats it isn't so much of a hurdle.

I see, thanks for that info. It does sound like it would turn my boat build into a research project.

I am now re-thinking the car paint option. Perhaps spray painting is not to be feared so much? I see that I can get a spray gun for ~50$, and I already have an air compressor of 1kW with 24l (6.3 gallon) tank. Throw in a full body suit and a face mask, some plastic tarp to cover everything in my dirty workshop (don't have a booth unfortunately), and maybe that would be enough to get a good and durable finish that would be harder and less laborious than using 2k polyurethane? Or am I underestimating the complexity of spray painting?

Compare gelcoat thickness to that of car paint. That is why even deep scratches "look fine" as its just thick pigmented resin. You could add copper powder, graphite is popular on bottoms, but really, they can all scratch given the right stone.

You mean mixing in these powders with regular (polyurethane) paint? Or any type of paint? Is that compatible with spray painting, or just for rolling/brushing?

 

[CarlosK2]

just the opposite: "gelcoat" is a thick layer of resin, "just thick pigmented resin" that is not comparable to a paint

What you want is called "gelcoat"

unless someone with more knowledge of this subject says otherwise, it is difficult to find something more resistant to (moderate) abrasion than a two-component polyurethane; but, of course, dragging a dinghy through sand and small stones is another level of abrasion

 

[skaraborgcraft]

You mean mixing in these powders with regular (polyurethane) paint? Or any type of paint? Is that compatible with spray painting, or just for rolling/brushing?

No, they are usually mixed in with epoxy resin, applied by roller, usually. Imron car clear coat can be applied by spray, if you have the facility for it. Its HARD.

 

[seasquirt]

I sealed a small dinghy bottom with straight (mixed) epoxy poured on and spread out quickly, and then brushed out, giving the plywood a glossy coat of armor. Did one side / panel at a time, having absolutely everything needed on hand close by. Lots of masking off, and tilting the hull for most level positions for the bow, and cleaning up excess quickly with rags.
A fibreglasser told me that the gell coat was the weakest part of a F/G hull, due to all the gloss and flow and cover additives.

 

[laukejas]

No, they are usually mixed in with epoxy resin, applied by roller, usually. Imron car clear coat can be applied by spray, if you have the facility for it. Its HARD.

Wait, mixed with resin, not the paint? It is still painted over, right? If so, what good do these additives do, if they are under the paint, meaning the paint can still be scratched?

I sealed a small dinghy bottom with straight (mixed) epoxy poured on and spread out quickly, and then brushed out, giving the plywood a glossy coat of armor. Did one side / panel at a time, having absolutely everything needed on hand close by. Lots of masking off, and tilting the hull for most level positions for the bow, and cleaning up excess quickly with rags.
A fibreglasser told me that the gell coat was the weakest part of a F/G hull, due to all the gloss and flow and cover additives.

You mean bare epoxy is left as the final surface? What about UV protection? Did you add some pigments or other additives to epoxy? In my case I definitely want some colors, so clear stuff is no good

 

[skaraborgcraft]

Wait, mixed with resin, not the paint? It is still painted over, right? If so, what good do these additives do, if they are under the paint, meaning the paint can still be scratched?

Epoxy "paint" is resin. Yes its added to resin. PU "paint" is resin. Seems to me its only called "paint", if its got a pigment added to it. What is epoxy primer but epoxy resin with a tint? No, its not painted over.

 

[skaraborgcraft]

I used both graphite and copper powder with resin on my daggerboard and box.