Ummm, yeah, don't use acetone. Word is that today's hardware store acetone may contain a number of disolved contaminates that can mess up epoxy. CLC recommends wiping down your surfaces with denatured alcohol instead. I haven't used acetone on my boat so I can't speak from experience there, but I've used a couple of gallons of denatured alcohol without issue.

Yes to sand it down. You will need to sand the contaminated surface to get rid of the contaminates or else you'll just have the same problem all over again. Do this carefully - you do not want to sand through the plywood veneer.

For an epoxy coat you do not need to sand to 220. 110 will do fine and give the epoxy something to grip. You'll want to sand to 220 when you're ready to move on to paint or varnish. 

Here's my opinion (boldfaced because you'll probably get many and all are likely to have valid ideas:

1) Sandpaper grade for final sanding of epoxy on the hull depends on how you're going to finish the surface; if you're painting the exterior, for example, 220 is probably unecessary.  Use 120-150 (or so) and get a smooth surface on which to lay down primer.  Smooth is the operative word here.  Don't expect primer to fill any gaps, gouges, or "raised areas" where epoxy may have run or dripped.  It will only cover minor imperfections (and you'll sand most of it off before painting).  Trying to use primer to fill significant "depressions" in epoxy will leave you with a kind of gooey, gummy mess that isn't sandable no matter how long you wait for it to dry (and yes, that is the voice of my experience talking there).

    For any surface you're going to finish with varnish, I think you're best off with 220.  Varnish is, for one thing, clear.  Imperfections in its undercoat will show.  Try to create a smooth surface in the underlying epoxy.  What I've been doing is wiping down the surface with denatured alcohol after sanding and then running my bare hand over it.  If I can feel imperfections, they will probably be visible.  And I agree with Chenier that denatured alcohol is a good idea.  I avoid acetone.  I've painted the exterior of my EP with Interlux Brightside (one-part),  and once the primer was laid down, I switched to Interlux 333 Brushing Liquid to wipe down sanded surfaces and prepare for the next coat (be sure to have adequate ventilation and breathing gear -- I wear a respirator -- when working with the Interlux products, especially if you're in a confined space!).

2) Bare Wood -- Yeah, it happens.  I had a few small spots where my sander got over-enthusiastic (always blame the equipment, not the user) and I took off all the expoxy.  This seemed to happen most often near the ends of the boat where only part of the random orbital sander was making contact creating an angle and sanding too aggressively (file that under "Lessons Learned").  I sanded those areas smooth with 150-180 and then applied fresh epoxy.  I then sanded those very gently with 220 just enough to get a smooth, contiguous surface with the surrounding areas.

I'm sure you'll get other opnions, and there will probably be good wisdom in all.  I don't think there's "one true way" to do these jobs.  That said, I hope there's a bit of merit to be found in the foregoing and that it's of use.

Good luck with your EP,

Roger 

Here's my opinion (boldfaced because you'll probably get many and all are likely to have valid ideas:

1) Sandpaper grade for final sanding of epoxy on the hull depends on how you're going to finish the surface; if you're painting the exterior, for example, 220 is probably unecessary.  Use 120-150 (or so) and get a smooth surface on which to lay down primer.  Smooth is the operative word here.  Don't expect primer to fill any gaps, gouges, or "raised areas" where epoxy may have run or dripped.  It will only cover minor imperfections (and you'll sand most of it off before painting).  Trying to use primer to fill significant "depressions" in epoxy will leave you with a kind of gooey, gummy mess that isn't sandable no matter how long you wait for it to dry (and yes, that is the voice of my experience talking there).

    For any surface you're going to finish with varnish, I think you're best off with 220.  Varnish is, for one thing, clear.  Imperfections in its undercoat will show.  Try to create a smooth surface in the underlying epoxy.  What I've been doing is wiping down the surface with denatured alcohol after sanding and then running my bare hand over it.  If I can feel imperfections, they will probably be visible.  And I agree with Chenier that denatured alcohol is a good idea.  I avoid acetone.  I've painted the exterior of my EP with Interlux Brightside (one-part),  and once the primer was laid down, I switched to Interlux 333 Brushing Liquid to wipe down sanded surfaces and prepare for the next coat (be sure to have adequate ventilation and breathing gear -- I wear a respirator -- when working with the Interlux products, especially if you're in a confined space!).

2) Bare Wood -- Yeah, it happens.  I had a few small spots where my sander got over-enthusiastic (always blame the equipment, not the user) and I took off all the expoxy.  This seemed to happen most often near the ends of the boat where only part of the random orbital sander was making contact creating an angle and sanding too aggressively (file that under "Lessons Learned").  I sanded those areas smooth with 150-180 and then applied fresh epoxy.  I then sanded those very gently with 220 just enough to get a smooth, contiguous surface with the surrounding areas.

I'm sure you'll get other opnions, and there will probably be good wisdom in all.  I don't think there's "one true way" to do these jobs.  That said, I hope there's a bit of merit to be found in the foregoing and that it's of use.

Good luck with your EP,

Roger 

   You mean we can pop off with opinions here? How can I pass that up -- especially since I am often viewed as a contrarian.

My opinions . . .

1.Yes. Try to get the hull free of contaminants. Sanding will do that, but there may be less abrasive methods to consider. If there are, you'd save work by using them. What's the advice from the pros about soap-and-water? Maybe wiping and rubbing with denatured alcohol would be sufficient?

2. The standard advice is that wiping with denatured alcohol shows you how the boat would look with a coating of varnish. I find that to be reliable advice.

3. My contrarian opinion is that a painted hull needs to be smoother than a varnished hull. The reason is that paint gives a uniform color and so any lack of smoothness in the surface shows up as a pattern of light and shadow. In contrast, the varied swirls and hues beneath a varnished surface conceal surface flaws and you can get away with some imperfections. In either case a perfectly smooth finish on a boat seems like wasted effort unless you plan to sell it rather than use it.

All,

I have accidently used acetone once and it was a shambles. I had some for a non-boaty project and the container was almost identical in color, size and labeling to the denatured alcohol container (thank you DIY store). The predictable happened and when I put on the glass it seemed to be fine, but after a couple of days cure it just started to peel right off. That's not supposed to happen with acetone, so it must have been contaminated. Sanding to bare wood, recoating with epoxy, waiting for a full cure, sanding again and then glassing took care of it. And it was no trouble at all - right! So avoid acetone.

Purchasing denatured alcohol has gotten weird these days. It disappeared from the websites of the DIY stores, except for one which sells it only in the 1/4 quart size for about what a gallon used to cost and labels it as window cleaner. But it turns out that a physical visit to the store still turns up lots and lots of cans, including gallon-sized, in the paint section for the usual price. It seems that California's the culprit. Due to denatured alcohol's health effects, they've passed laws limiting the quantities that can be sold and it appears that the DIY stores have decided that customizing their websites on a per-state basis is not worth it. So, depending on your state, it may be freely available at your local store even if not listed on the website.

Birch2,

Sorry to mess with your self-image, but I heard John Harris articulate that exact same opinion, especially for sprayed glossy paint, at Okoumefest so long ago that it was still being held at Camp Letts. So while you may not be a contrarian, at least you're in excellent company :-)

Laszlo

   Thanks for the feedback.  I've been to the store, bought penty of denatured alcohol and sanding disks, ordered more epoxy, and I am preparing myself for lots of cleaning, sanding, and re-epoxy-ing.

So far, the boat doesn't look universally horrible.  Its been 3 days.  Large sections look okay.  No peeling.  Maybe I got lucky?  

 Started sanding last night.  The epoxy did not "peel", but I seemed to get to bare wood quickly, except some spots seem very hard to sand down - what's left at this point looks kind of like mottled dark spots, and in some cases fish scales sprinkled on th surface.  Otherwise, I think I am getting to bare wood.  It looks like bare wood.  I'm not sure what sanded epoxy is supposed to look like.  If I wipe it down with denatured alcohol, it looks nice. The one video isn't a real clear picture, "Part 12 - Building a Stitch-and-Glue CLC Kayak", but what I have looked a lot like the before picture, and now looks a lot like the after picture, too.  Can someone describe what the sanded epoxy where there is no fiberglass is supposed to look like?  Maybe I have none, and that is why I can't figure out what it is supposed to look like.