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njcoaster
04-17-2003, 10:01 AM
I am getting down to the end of my project - a 12 foot skiff of my own design. I am a little burned out on the project, and I may be trying to force the endgame a little. I got sick and tired of sanding the epoxy-over-glass-cloth hull and started laying on spar varnish. Looks lumpy. I can live with it, but I was wondering how you get a smooth finish when you are using cloth over ply. I rolled the epoxy on, and I smoothed it with a vinyl scrapper, but a lot of lumps remain. Given the hardness of dried epoxy, and the way it gums up sandpaper in just minutes, what is the best way (next time) of avoiding lumpiness in the first place, or at least getting rid of it without spending dozens of hours sanding?

I know some will say "lapstrake!", but let's assume I'm sticking with plywood. Someday I'll build one that's like a cabinetry project, but right now I only have time for quicky boat building.

Scott Rosen
04-17-2003, 11:20 AM
The easiest way is to paint instead of varnish, especially if you're in a hurry. Before painting, fill the weave with epoxy fairing compound, sand fair, and paint.

I think you will find that the extra time it takes you to get a great bright finish, and the unpleasantness of working with epoxy, will have you wishing you chose a different method.

Frankly, I never thought much of varnished plywood, anyway, unless you are willing to spend the extra money for a varnish-grade veneer. The trouble with varnished plywood, is that it still looks like plywood even if you do a Bristol varnish job.

Bruce Hooke
04-17-2003, 11:30 AM
Can you tell what caused the lumps? Was it dried bits of epoxy in the mixing cup or the roller tray, bits of glass cloth that got picked up, a less than clean edge on the vinyl spreader (scrapper)? Care in these sorts of areas will pay off in the long run, but there are some that you can't do much about -- like picking up bits of glass cloth in the process of applying the epoxy, but you can limit even this by not overworking the surface.

Also, you don't say if you applied additional epoxy over the cloth. The normal procedure in my experience is to apply the cloth with enough epoxy to fill most of the weave of the cloth, but no more. Once this cures a light sanding should knock off any bumps. This is also a good time to fill any major dings and fair any major problem areas with thickened epoxy. Then another couple of coats of epoxy can be rolled on to smooth the surface. These coats should normally NOT be worked over with a spreader. The roller should leave a smooth surface on it's own.

Finally, as far as the sandpaper getting gummed up -- this could be a result of the epoxy not being fully cured. It could also be an issue with amine blush, which can be washed off with water after the epoxy cures...

njcoaster
04-17-2003, 12:10 PM
Actually, this is opaque blue varnish. I'm not going for a bright finish. Lumps are from bad "hospital corners" at rear of boat, bad overhead lighting in garage, and some sagging on sides where I must have applied too much gunk. Also, got a bunch of sawdust into my epoxy can.

This is a utility boat. Fishing is my goal, not boat shows, but I wish I had been more careful. I am a catalog of leasons learned.

Bayboat
04-17-2003, 12:15 PM
A good way to prepare a 'glass/epoxy surface for the next coat, and for varnishing, is to go over it with a very sharp cabinet scraper. It gets rid of the little dust bumps better than sanding.

Bruce Hooke
04-17-2003, 12:36 PM
Sounds like you've nailed down fairly well where things didn't go as well as you would have liked, which should allow you to do better next time. That's the only way most of us learn... :D

At corners it is often preferrable to cut away some of the cloth rather than building up too many folds.

What do you mean by "opaque blue varnish"?

As far as epoxy being hard to sand, one thing I learned from hard :D experience is not to let the epoxy cure too long. In most cases it is ready to be sanded the next day, however it will continue to harden for a long time after that. So, if you wait until the next weekend to do your sanding it will be a lot more work than if you get to the sanding as soon as the epoxy has cured enough. Just make sure to protect your skin, eyes and lungs because you will be sanding incompletely cured epoxy, which is not healthy to breath or have on your skin.

NormMessinger
04-17-2003, 12:53 PM
Use wet/dry sandpaper. Water will keep it from gumming up and carry away any amine blush you might have.

njcoaster
04-17-2003, 02:07 PM
Wet sandpaper sounds like a good idea. I am not a fan of toxic dust, which is one reason I hate sanding. I now use water and a plastic pad to prepare wood for interior housepainting in order to keep lead dust down. I guess I have to spread Epoxy a little thinner, too.

As for the "varnish", maybe it is paint, come to think of it. That sounds stupid I'm sure. Oil-based, off the shelf from a West marine store. I thinned it a little with solvent they sold me. I could swear the guy called in varnish, but he also said it was water based, so maybe he was a little mixed up. I thought there were tinted varnished out there and I didn't give it much thought.

I am using gray home depot porch paint for the interior.

John Blazy
04-17-2003, 02:19 PM
I should have gotten a round tuit by now, but I plan to glass the hull of my boat bright (nice stained mahogony-like face veneer), using 6 oz glass and laying 30 mil polyester film into the final, wet epoxy weave-filling coat, then rolling out the bubbles. This will minimize fairing drastically, by simply peeling off the film after the epoxy cures (epoxy doesn't stick much to PET, as opposed to acrylic - found out the hard way), as the epoxy will conform to the smooth curve of the film. From the smaller pieces I've done before this way, the surface is almost glass-flat and only needs minor scuff sanding for the varnish layer. The best part is that the surface looks like glass with perfect feathering of thick areas to thin areas.
Hope it works, as I weild a 14 foot piece of scarfed film into wet epoxy :eek: .
Will report good results. If you don't hear from me, then . . . well . . . :(

Bruce Hooke
04-17-2003, 03:15 PM
John, The key thing I'd be worried about is wrinkles in the plastic. I think you will have a very hard time getting a sheet of plastic to lay absolutely flat over that large an area. Note that I think that even what you might call "hints of wrinkles" will cause problems - in other words if the plastic is just a bit off the plastic may wripple a little without actually wrinkling. Those ripples may well get reflected as varying thicknesses in the epoxy.

Bruce Hooke
04-17-2003, 03:19 PM
One problem with wet sanding is that the slurry the sanding produces can make it much harder to tell whether you've sanded enough (or worse, and all too common -- too much). So, if you wet sand you may find that you have to clean the surface very regularly to see your progress.

Also, I do most of my sanding with a random orbit sander, which I don't think I would want to use around lots of water...

As to the "varnish" -- that sounds to me like what I'd call "paint", but the whole water-based finish area is still pretty new to me so I don't know what the paint companies (and salespeople) may be calling some of the stuff!

John Blazy
04-17-2003, 07:48 PM
Hey, Bruce - good concern. If one end sags even a little, the resulting hump is one large wrinkle. You probably don't realize how thick 30 mil is - .030" or almost a full 1/32" which is difficult to wrinkle. I even considered 1/16" (.062") acrylic, but would likely spring straight and delaminate at the edges. The PET I'll use is print grade - real flat, 'cept at the scarf joint.

Bruce Hooke
04-17-2003, 09:00 PM
John - Your right -- actually, I pretty much glossed over the 30 mil part rather than stopping to think about it. You certainly should not have problems with wrinkles! I do wonder if you will have trouble with things like the weight of the plastic pushing down more at any edges and making the coating too thin right at the edge. In any case, it's an interesting idea so keep us posted on how it works out...

JimConlin
04-17-2003, 09:12 PM
I've done a couple of trials of using peel ply to level the epoxy filling of 6 oz. glass over mahog. The results were promising, a flat surface with the cloth filled and a texture that would be excellent for secondary bonding. I need to experiment with how much sanding that surface needs before varnish. I'm hopeful that I can save 1-2 coating steps and a nasty sanding step.

njcoaster
04-18-2003, 09:49 AM
One part Polyurethane paint was what I was applying. I should read labels a little more carefully! I thought it was a polyurethane "spar varnish" type product.

Looking at it again, it isn't so terrible. The sags are a little bit of a bummer. Little boogers and bumps are easy to sand off, but the long slow changes in thickness require a lot of sanding time that I am not willing to commit to.

A classic mistake I made was to add too much epoxy and make a mental note to "fix it later" by sanding. Later it is very tempting to simply live with what you have.

Some day this boat will be finished. I tell my wife that the day it's done I'm going to take a fire ax to it to pay it back for all the grief. "You'll never live to see water" I tell it. But I'll do another.