Recommendations on paint over epoxy?

Discussion in 'Fiberglass and Composite Boat Building' started by leaky, Feb 10, 2014.

  1. leaky
    Joined: Sep 2008
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    leaky Senior Member

    Hi,

    I've got a bunch of plywood laminated with marinepoxy (the duckworks stuff). I need to select a paint. It is going in a 1973 aluminum boat that I just fish with (no chance of it ever seeing wax or a buffer).

    Shine is less important than durability and ease of use. Mostly the paint will be going on the deck and sub-deck storage areas. For the deck non-skid will be added of some sort (maybe just salt on top when it's wet, maybe grit mixed in).. Ease of re-coat would be nice, because mostly it will be on a deck I'd like to be able to lay on additional thick coats as-needed without major prep (sanding/washing is fine, I just don't want to need to strip or tie coat).

    I would rather not go through the process of spraying (want to roll or brush) and would prefer working with something that is tolerant to being applied in colder temperatures (OK if it takes days to dry, just needs to do so eventually ). I can coat outside (which may be 30's) and move into the basement for drying if the fumes aren't too bad (50's)... or I could coat in the tent I'm working in and keep the temperature as high as 80, however it's only practical to keep it that warm for a few hours at a time. I don't care about how toxic the stuff provided a standard respirator is OK.

    I'm not real experienced with paints. Gel coat I've done (over epoxy even) - it's a pain if you want to work under 70 and especially over epoxy.. Single part polyurethane I've done and never had good luck with it - too many problems drying and seems to be counter-acted by 2-part epoxy.. Truck bed liner also have used but have had adhesion issues (ie dries OK, flakes off a year later). Figuring start right and use something better this time.

    Thanks in advance!

    Jon
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You have a number of choices, from house paint to the stuff they use on the nose of rockets. They'll range in price from $20 to hundreds (some thousands) of bucks a gallon.

    For you, acrylic Porch and Deck enamel is the low cost, low VOC, easy to apply and easy clean up stuff. It's fairly hard and fairly durable. It's not as good as the $400 a gallon stuff, but it costs a whole lot less.

    Look up the "roll and tip" method on this site (and others). You'll find you can apply paint really close to a spray job, with just a roller and brush.

    Start with a good primer over a well cleaned, and well scratched epoxy surface. 100 - 120 grit is fine for what you want. don't go over 280 (220 is much better) or you'll have adhesion issues. For a roll and tip job, 120 is more then sufficient, as the paint will fill any scratches.
     
  3. leaky
    Joined: Sep 2008
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    leaky Senior Member

    You figure that will hold up to boots and grit? For the deck, which is most of it, I will be mixing something in, and that does tend to make it wear faster. I guess I under-estimated how tough it could be and wrote it off.

    What would be considered a good primer?

    Just wondering, anyone know the system III 2-part polyurethane works? Tougher or just a better finish? How about something like awlgrip?

    Rolling on water based paint sure would make things simple!

    Thanks,

    Jon
     
  4. SaugatuckWB
    Joined: Jan 2014
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    SaugatuckWB Junior Member

    I did a test on my boat between light grey water-base (Sherwin-Williams) and oil base porch paints (Valspar). Both were covered with sand on the first coat while the paint was wet. When dry, the sand was swept off, vacuumed and the second and third coats applied. Water-based was used on the upper deck and oil-based on bow deck and cockpit sole. I used Valspar oil-based primer under both. They were applied over plywood covered with fiberglass cloth and system-3 epoxy.

    The water-based paint was drying too fast (it was hot) to do the whole deck (10'x12') in one coat and still get the sand in it before it dried. I ended up with lap marks where I painted an approximately 3'x5' area and then covered it with sand then painted the next section. So it didn't look that great, but it really didn't matter because there is furniture up there so you don't see it much.

    The oil-based I covered in one application of paint then folllowed up with sand in a metal can with a screen on top to spread the sand thickly over the whole surface. It turned out very nicely and uniform after sweeping and vacuum.

    Three years later and the oil-based paint is holding up well with no peeling or scrapped up areas. It does hold some dirt in the grit so isn't the easiest ti keep clean. The water-based paint is peeling in a few spots and has worn through in a couple of places from foot traffic but also chair legs. To be fair, there aren't any chairs where the oil-based paint is so I don't know if it would be that much better.

    The whole boat is getting painted this spring and I'm going to have to strip the water-based paint and recoat with oil-based. The oil-based areas can get by with just a couple coats of paint.

    By the way, its really hard to sand off paint that has sand mixed in so I'll have to use a chemical stripper.

    I think using salt as a grit would probably cause some problems because of its water solubility if the surface gets worn a little bit and the grains are exposed. And I think using a water-based paint with it would be a problem for the same reason. Most people use sand. I got mine from the Lake Michigan beach, very fine and uniform grain size. I sifted it through a couple sets of window screen and then put it in bucket with water to float out other materials like wood, etc. After several rinses and drying in the sun it was much better than sand you'd buy for mortar or something. I'm sure they sell sand already prepared. It seems I mixed some in paint for porch steps years ago. Pre-mixing with the paint doesn't give you a very uniform distribution and its hard to get very much grit in the paint without it turning to mud and being impossible to apply.
     
    Last edited: Feb 11, 2014
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The technique described above is what I recommend, instead of mixing in with the paint. I strongly recommend you don't use sand as the texture. It's easy to get good results, but it's a ***** to repair and/or remove when this time comes (it always does). I prefer polyurethane texture granulates, which is available in different "weights" at any real paint store. These are broadcast over wet paint, permitted to dry, any excess vacuumed off and recoated, to lock down the particulates.

    The issues SaugatuckWB had with his acrylic paint job, wasn't product related, but environmental conditions related. If it's too hot and the paint is drying too quickly, you need an acrylic "wetting agent", to extend drying time, so the texture has some paint to grab a hold of.

    In terms of durability, both the low end alkyds and acrylics seem to perform about the same. The oils can be a wee bit tougher, but it's a marginal call and it's more trouble to clean up, compared to acrylic.

    The System Three WR-LPU isn't very good IMO. I've not had great success with it. Some swear by it, but for it's cost, I have other choices. If going for a two pack paint, use a solvent based product, which will perform very well. Awlgrip will be a good choice, but is considerably more expensive than house paint.
     
  6. SaugatuckWB
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    SaugatuckWB Junior Member

    The issues with the water-based paint drying fast were both environmental and product related. The hot temps (90-ish, but not in the sun) made the difference in the drying time of the paints an issue. But the oil-based was applied the same day and needed no additive to remain wet long enough to apply the sand. Using an additive may have helped with the water-based. Hard to say at this point. So the environment was the same for each type of paint, yet the oil-based performed better.

    The durability issue I'd say was almost exclusively a product issue. Even if you ignore where the chairs have gouged the paint, the water-based is still not holding up as well to foot traffic and the sun. And some of the wear, etc. is in areas that don't have sand in the paint, so that isn't the cause.

    If you can get something other than sand to add I would try it because of the problem with removing it at some point. I have three years of charter boat use on the decks and the oil-based just needs more paint, no removal yet. Maybe in another three years it will be an issue. The water-based needs removal this spring.

    Clean up is obviously an advantage of water-based paints, but I do so much other painting and varnishing that its just part of the job to clean brushes, etc. I don't even think about it anymore.
     
  7. leaky
    Joined: Sep 2008
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    leaky Senior Member

    Will the oil based paint usually work OK over 2-part epoxy? Is it good to get a marine paint versus just hardware store stuff? (durability my #1 concern)

    I guess if I was going to do something cheap that is a good option too. I've had good luck with oil based paints. It can be fairly tough and also provides a degree of moisture resistance, easy to re-coat, plus if I decide some day I want to coat the deck with something else, most things go over it, eliminating the need to strip (where as latex you would not want to use a primer for other things I think)..

    Prior I was just using rustoleum over the bare plywood. It worked OK for awhile and was stupid easy to re-coat.

    As far as primers go, anything in particular?

    Thanks,

    Jon
     
  8. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    I actually like to use a 2K epoxy primer/undercoat on the epoxy. The Hempel one is good in the EU but not cheap. It will fill any 'pin holes' in the epoxy sheathing and give a good base for the top coat(s). Cheapest durable top coats in my experience are Hempel or Epiphanes one pack polyurethanes. Generally better than the alkyds, which are OK if you get enough thin coats. In the US you may have different brands, I expect PAR will give you a good steer. You will need at least 10 deg C to get a cure though. If it is too cold it will go off OK if you just raise the temp a bit even after 12 hours it will work. Don't ask how I know...;) As long as it is dry, you will have no problems with those one packs.

    Another 'thick' primer is the automotive PPG acrylic/polyurethane undercoat Kobe which uses a 5:1 ratio paint to hardener and is a 2K paint. Nearly as good as the epoxy primer. This like the epoxy will let you fair a surface well and is a reasonable substrate.

    I'l also second using a mini gloss roller with the top finishes. You get very close to a spray quality, especially if you de-nib and/or fully rub down with wet or dry. If you have a lot of curved surfaces, a good trick is to saw the roller size down to get it more even round the curved surfaces with an even coat. Second the anti slip granules too, sand is too vicous and tears the hell out of skin with unwanted contact!.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Some alkyds (oils) can have a bad reaction (will not stick/cure) with unprimed epoxy surfaces, but most other paints can be applied directly over cured epoxy. It's always wise to prime first and an epoxy primer is the way to go. Polyurethanes are a little more expensive in the USA, compared to straight alkyds, but not by much and generally are better, if your budget will tolerate it.

    Sand is the worst particulate you can use for texture, mostly because you need a diamond blade to remove it when the time comes. Over coated a sanded surface will smooth it out enough to be comfortable, but there are much better materials, like walnut shells or polyurethane beads, both of which can be easily applied and removed with conventional techniques.
     
  10. leaky
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    leaky Senior Member

    Thanks! I'll go hunting around for a primer and take it from there.

    Polyurethane sounds good, and I really do not mind spending the $$, but on 2-3 different projects I've pulled my hair out with it - excessive dry times. I think it's a temperature problem as I'm always doing these things during the winter (ie summer is for fishing ;) ) The max temperature I can sustain is 50 degrees F and in the process of painting it's going to be closer to 30 degrees F until I move it into the basement to dry... I can fire up heaters and keep things very hot for awhile, but anything that takes a day to dry isn't going to get a full day of heat.

    We think 2K epoxy primer will work OK? I ask because we had some bad experiences last year on a friends deck and 2-part epoxy primer he uses at his body shop - similarly to what can happen with gel coat, it would not cure on the epoxy. We wrote it off as incompatible.

    For sure I won't just use sand - in the past I've bought the grip stuff. As you said makes a mud out of the paint (applied well only in a messy manner via brush). Will try casting it out and see how that works.

    Painting is the one thing I've come to dislike about 2-part epoxy. With polyester blasting on a thick coat of $60/gallon gelcoat would have been a no-brainer.

    Leaning toward the latex - I know going that route I can re-supply at Loews and won't get bogged down in painting problems.

    Jon
     
  11. alan white
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    alan white Senior Member

    I have refurbished restaurant equipment (usu. big ovens) to look as new using Rustoleum (though I am not specifically recommending it. Follow PAR with the paint type advice). I just wanted to mention that when the surface is flat like decks are, you can thin the paint considerably and lay it on with just a roller--- no brushing. I always got spray-look results. Drips would occur on vertical surfaces at that level of thinness of course. You can paint vertical areas first and while still wet, roll out the flats.
     
  12. missinginaction
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    missinginaction Senior Member

    Just thought I'd weigh in as leaky said the durability was his #1 concern and he'll be walking on the decks.

    I'd highly recommend using a 2 part linear polyurethane paint.

    I've had great results with Interlux Perfection paint.

    Perfection is applied over a product called Interlux Epoxy Prime Coat. The primer is applied over properly cured and prepped bare epoxy resin. These two part LPU's are very hard and wear very little over time. You can sprinkle a product called Intergrip, a non-skid compound, over the wet paint and make yourself a nice secure deck. The nice thing about Intergrip is that it is designed to give you secure footing but also be easy to clean. It doesn't trap dirt like sand and doesn't feel sharp or "gritty". You can kneel on it and not be uncomfortable. I'm not a chemist or engineer so I can't speak to the mechanics of the Intergrip but it performs exactly as the manufacturer states.

    It's true that these products are a little pricy but they work. My only advice is to read and follow the manufacturers instructions exactly. Some people will tell you that 2 part LPU's are difficult to work with. I did not find that to be the case. I'll put a link below and you can look for yourself. Good luck with your project.

    www.yachtpaint.com

    Oh, not to hijack the thread but a note to PAR - 12 below this morning. Forecast....snow starting again tomorrow morning. 12" to 16" expected. :rolleyes:
     
  13. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Agreed LPU's are the way to go, but the costs can be intimidating. Single part polyurethanes can get nearly as good of results as the LPU's, but at a greatly reduced cost.

    I'm not sure of your epoxy primer on raw epoxy previous experiences, but almost all of these "compatibility" issues, can be traced back to an error in application. In the case you mention, a blush on the raw epoxy surface may have been present, so that any over coats wouldn't bond well (this is a educated guess anyway). Generally, using known compatible products is best. If not that familiar with the products, the usual advice is to stick with the manufacture's recommended primers and paint combinations.

    12 below, damn and I was bitching about it being in the 50's the other weekend.
     
  14. Jim Caldwell
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    Jim Caldwell Senior Member

    Par, that freezing for Crackers! ex cracker myself.
     

  15. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Never had a problem with 2K epoxy, but the epoxy sheathing (on plywood) was abraded thoroughly. There was no amine bloom or any trace of stickiness prior to application. I usually wipe clean thoroughly with Acetone as well and then hand off, and dust off any other dust or particulates. Done quite a lot of new hulls/repairs on new ply or solid this way, no problem at all. Top coats have been 2K or one pack.

    Another useable primer is a 2K polyester automotive one. Watch out if you spray this as the cure time is pretty fast!. Only just saved a gun on one occassion. If you are really crafty if you get the cutting of it right in the cure, it is like butter with wet and dry.
     
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