Clear coat

[donwells]

I am going to take this canoe to a paint shop and have it shot with clear coat as the final finish instead of varnish.
I know that when they shoot clear coat over new paint that it is not sanded prior to this step.
My question is this, beings this is epoxy instead of paint can it be shot directly onto it or should i
still final sand the epoxy prior to them shooting the clear coat?

 

[Jim Dodd]

I'm no expert, but the guy who is spraying on the clear coat should know.
My concern is if your epoxy has a amine blush? That would need to be removed. I believe some use a wash to remove it. Acetone has been used by some with good results.

Sanding very lightly, say with 320grit, would provide Tooth to hold the clear coat.

Again talk to your painter !

Jim

 

[Todd Bradshaw]

All it takes to remove amine blush is a Scotchbrite pad and plain water. Adding other chemicals or solvents is more likely to contaminate the surface and inhibit the bond of anything you put over it than do any good.

A point of order - epoxy resin is not paint and doesn't go on as smoothly as paint, no matter how you apply it. If you simply varnish, paint or clear coat over it, it will generally look pretty bad, and those top coats will not fix the uneven surface. If you want a decent, professional looking finish over epoxy it has to be sanded smooth first. This is generally done by starting out with paper in the 80-100 grit range, then something like 150-180 grit and then maybe up to 220 for a clear finish. Going finer than that will often reduce the bond quality of your topcoats, but you can check with your painter and see what sort of tooth he wants to spray over. You also want to make sure that your topcoat contains a good UV absorber to protect the epoxy. Unprotected epoxy resin can start to break down in as little as a couple hundred hours of exposure to UV from the sun. Paint, on the other hand, will usually block UV at the surface, protecting the epoxy from damage, which is why so many epoxy-clad boats are painted, rather than clear-coated or varnished.

 

[donwells]

Thanks guys, that is pretty much where my brain was heading but i didn't know and figured i would
get some advice from those that had more practice than myself. I have gotten all of my stuff from
RAKA and have had no problems with anything as of now and i haven't had amine blush I don't know
if i have been lucky or it is just the product. Thanks

 

[Jim Dodd]

Raka with the 350 hardener is non-blushing.
I'd have to agree with Todd on the procedure.

Jim

 

[donwells]

I just called the guy that is going to shoot this and he told me that after i get my final coat of epoxy on the canoe
that it would need to be scuffed up and suggested that i either use a gray scuffing pad or if i use wet or dry paper to
use either 1500 0r 2000 grit he also said that if you do wet sand that you will have a finer finish than if you were to
just dry sand it but it definitely needed to be scuffed.

 

[Todd Bradshaw]

Sure, you can scuff it and spray it, but if you don't sand it smooth before painting it will forever look like it was built, glassed and varnished by a rank amateur who didn't know any better, and the most fabulous spray job ever done isn't going to cover that. It will only make it more obvious. With a $50 random orbit sander you can sand the filler coats smooth as a baby's bottom in a couple of hours of work and get it ready for a beautiful finish. After all the work it takes to get this far, it seems like a real shame not to finish the job properly, but to each his own.

 

[Jim Dodd]

Again I agree with Todd.
Before thinking of clear coat, you need to work the epoxy smooth, without getting into the weave of the cloth. I start with 80grit, and finish with 120grit, before I foam brush Spar varnish.
But if your painter recommends a fine sand, he certainly knows more than I do, as I have never sprayed on a finish.

Jim

 

[donwells]

Sorry, I think you are misunderstanding i have gone through all of the filler coats and it has been sanded down and smooth
I am now going to put on my last coat to make sure all of the scratch/scuff marks are covered then go over it with the 1500
paper before it is shot with the clear coat instead of varnish. you guys may be right, I have read that clear coat is a better
uv inhibitor than varnish is and goes on in a thicker coat. I sometimes learn the hard way so if it does come out bad i
can always sand it off and go back with varnish of some kind then i will for sure know better the next time. this one is mine and not for someone else..

 

[Jim Dodd]

Sounds good ! Keep us posted.
I've always wondered about the clear coat, and like you, have read some posting on it.
Jim

 

[Todd Bradshaw]

Doesn't sound good to me, as you would basically have fixed the problem by sanding it smooth and then will create it all over again by applying another coat of resin. If you want to learn how to work well with epoxy, you really have to understand that it isn't paint and doesn't flow out or shrink down smooth the way paint will. It doesn't matter what method you use to apply it, or how good you are at doing it, there is no way you will end up with a truly smooth and fair surface with unsanded resin on top, and 1500 grit doesn't do much more than polish it. It's not coarse enough to do any cutting/leveling. Best case scenario, even if you do a fantastic job of applying it, would be a lot of orange-peel to your surface - and when you get to a viewing angle where you are sighting down the side of the boat it is going to look very rough.

Since a lot of body shops shoot their clearcoat over 800-1,000 grit, I even wonder what sort of adhesion you are likely to get over 1,500. When I looked into clearcoat, I also found a curious thing in the instructions of some where they listed UV absorbers that protected the clearcoat itself, but apparently not what was under it. They specified that your paint layers (or whatever) under it needed to provide their own protection. I'm not a paint chemist, so I don't know what's up with that, but it didn't sound very good for use over clear epoxy that absolutely needs good protection. In the long run, I think there is a pretty good reason that nearly all strippers are finished off with a good, UV-filtering marine varnish.

 

[Jim Dodd]

Don. Todd is right about the final coat of epoxy you want to apply. It is NOT self leveling, and more likely to run on the vertical surface. Bringing you back to sanding with a course grit again.

The hull is sanded now, why do you want to apply another epoxy coat ?

Jim

 

[garypete]

Clear coat UV protection: I'm eight years into a non-scientific test on the UV protection of 2-part polyurethane auto clear coat vs spar varnish for epoxy/fibrerglass substrate, and the results are encouraging.

I used 1 x 1 cherry strips to glue up a tailgate panel for my utility trailer. I coated the outside of the panel with fg cloth and epoxy, sanding it smooth to 120 grit like one would do on a cedarstrip canoe. My body shop sprayed on 3 coats of 2-part polyurethane clear coat in just over an hour, letting each coat flash-dry for about 20 minutes. The inside of the panel was painted with 2 coats enamel paint so seal out moisture.

For eight years, I intentionally parked the trailer with the tailgate facing south to get direct sunlight. It got splattered with sand and gravel occasionally when I was sloppy with the shovel at the gravel pit. I backed into a couple things, and the panel of course got rained and snowed on for eight years.

The only difference I can see in eight years of abuse and direct sunlight is that the gloss finish has become a satin finish. There's no deterioration of the epoxy, the fg cloth is not turning black as happens with spar varnish after 3-4 years of not recoating, and the clear coat finish seems pretty near bulletproof. I now use clear coat on all my strippers as I'm sold on it.

The often-mentioned difficulty of repairing scratches in super-hard clear coat has now been solved with the development of brushable clear coat with even more UV inhibitors than sprayed auto clear coat. I get mine from Progressive Epoxy Polymers, Inc. The brushable clear coat is called ACRYLIC POLY UV PLUS. It's brushable, but only for about 30 seconds after lifting the brush out of the mixed liquid. Rolling with a foam roller is the preferred method, giving about a minute of working time. With either method, the finish is high gloss. It can be made into a satin finish by rubbing with very fine steel wool within an hour after application.

One caveat: if you're panning to spray clearcoat directly onto wood which has not been covered with fg cloth and epoxy, and sealed on the other side, be sure the wood has been kiln dried. I had an air-dried white oak transom plate on a fishing boat sprayed with clearcoat after just rolling on two coats of an epoxy to seal the wood from moisture infiltration. Left in the sun for a week, unsightly large bubbles popped up, the residual moisture in the air-dried wood rising to the hot surface. I had to sand and recoat the wood three times before the bubbles quit coming out.

 

[garypete]

Epoxy prep for spraying automotive clearcoat:
I've had several canoes sprayed with clearcoat with excellent results. It flash dries in 20 minutes, so a good body man with an HVLP gun can put on three coats in a little over an hour. Each coat has three time the UV resistance of a coat of spar varnish, so the three clearcoats layers have UV resistance nine times the UV protection of one coat of spar varnish. And the UV properties seem to last forever. Have you ever seen a faded paint coat on a modern base coat/clearcoat car?

I sand the epoxy to with 120 then 220 grit and the clearcoat fills in the scratches nicely; there's no need to sand with any finer grit, and like Todd mentions above, you may actually lessen the adherence of the sprayed clearcoat if the finish is mirror smooth, e.g. 1800 grit. The sanding however must be thorough as the clearcoat will not fill in the fish eyes of an orange-peel layer of epoxy. If you prefer a satin finish rather than high gloss, your body man can add a flattening agent to the paint.

I love the sensual experience of brushing on a flawless coat of spar varnish as much as the next guy, but I don't have ten days to brush on five meticulous coats of spar varnish with five days of wet sanding in between in between. And all for a finish that is so soft it scratches easily and only protects the epoxy underneath for about three years. Unlike the way I had to baby my spar-varnished strippers, I leave my clearcoated cedarstrips outside all year and bang them down some pretty heavy rapids.

 

[Jim Dodd]

Thanks Gary ! You sold me !
I'll have a new hull soon, and I'll check with the local Auto body shop.

Any cost ideas ?

Jim

 

[garypete]

It varies depending on the curiosity of the body man and how much spirit he has for new adventures. One guy sprayed a canoe exterior three coats for just the cost of materials ($125) as he was so glad not to be spraying a car as usual. Another shop charged materials and one hour of labor for the painter ($225).

It's not rocket science and you can easily do it yourself if you have a good HVLP gun.

Gary