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is all of this sanding necessary?
ok, so, we've all heard the old adage that boatbuilding is "90% sanding". All jokes aside however, I have a couple of questions about how much sanding is actually necessary.
In the Eastport Pram manual, 2 coats of epoxy on the entire boat are recommended. It seems to me that a minimum of four coats is more appropriate. My orbital sander with 220 grit at the lowest speed goes through two thin coats of epoxy faster than a hot knife through butter. I've resorted to sanding the entire boat by hand because the orbital sander just puts holes in my epoxy (yes I'm being very careful, yes I'm using a light touch, keeping the sander moving, not revisiting spots I've already sanded, etc...etc....).
Sanding an entire boat by hand (even a boat as modest in size as the EPP is horribly tedious.
Two questions:
1. Can someone enlighten me as to how this can realistically be done with an orbital sander without putting holes in the epoxy?
2. If your epoxy coating is pretty smooth to begin with - what actually is wrong with putting primer and paint, or varnish over lightly sanded, or not so sanded but otherwise smooth epoxy? Why is that a bad thing for the final finnish?
3 replies:
RE: is all of this sanding necessary?
Thom,
Congratulations, you have achieved the Holy Grail of being able to apply very thin coats of epoxy. That means you'll waste less and have smoother coats with no drips. If your coats are that thin, you'll need more coats before sanding. I usually apply 5 before I start sanding. What you want is enough to mostly fill the weave, then sand, then a couple of more coats and the final sanding. The manual is written for the average first time builder and they tend to put on thick coats. You need more coats to get to that thickness. Once the thickness is right, you should have no problem with the sander.
There's nothing wrong with paint or varnish on a lightly sanded boat. It will float just as well. Yacht finish snobs who can't see past the outer 0.020" of a boat will say you don't have pride in your work and you won't win awards for best in show because they usually don't consider much beyond the finish, but who cares? A workboat finish is perfectly respectable and most boats since the dawn of time, including the ones that can destroy entire nations, have had them.
Laszlo
RE: is all of this sanding necessary?
On my NE Dory build I used an orbital on the outside of the hull and found it tricky enough to control. Today I'm sanding the interior in preparation for varnishing, and for that I'm using a quarter-sheet shander (23$ from Amazon), which in this application is better than the orbital: not too powerful, light, the sanding surface is small, and the sandpaper is much cheaper. Even with that I accidentally took the finish down to the wood on one small spot on a rail. So from now the rule is that anything smaller than the sanding sheet is done by hand.
As an aside, parts of my interior are a little rough. I made a slight mistake (?) with the epoxy. I'm building a dory at the same time of the sail kit and of course ran out of MAS. This brand is not sold in my geo so I had to switch to WEST with 207 hardener. The first time I used it was on the dory interior and I was caught be surprise at how quickly it cured (like, 12 minutes). So I put it on a little tacky, which made a very rough finish.
RE: is all of this sanding necessary?
» Submitted by Laszlo - Thu, 7/13/17 » 10:06 PM
Thom,
Congratulations, you have achieved the Holy Grail of being able to apply very thin coats of epoxy. That means you'll waste less and have smoother coats with no drips. If your coats are that thin, you'll need more coats before sanding. I usually apply 5 before I start sanding. What you want is enough to mostly fill the weave, then sand, then a couple of more coats and the final sanding. The manual is written for the average first time builder and they tend to put on thick coats. You need more coats to get to that thickness. Once the thickness is right, you should have no problem with the sander.
There's nothing wrong with paint or varnish on a lightly sanded boat. It will float just as well. Yacht finish snobs who can't see past the outer 0.020" of a boat will say you don't have pride in your work and you won't win awards for best in show because they usually don't consider much beyond the finish, but who cares? A workboat finish is perfectly respectable and most boats since the dawn of time, including the ones that can destroy entire nations, have had them.
Laszlo