Epoxy Skimcoat

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MattGoose
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Epoxy Skimcoat

Post by MattGoose »

Hi - long time board member, very rare poster :)

I'm finishing a stitch and glue kayak I started last summer and I'm working through the final epoxy "skim" coats and then will be moving to varnish.

I put on the last skim coat yesterday and about 95% of it came out great - but there are spots where the epoxy is very thin. It had been awhile since I put some down and I didn't mix enough and it started to kick on me :)

Can I just mix a bit more and put it down over those thin areas?

In a related question, how well does varnish flow in and fill (very minor) low spots?

Thanks!

Reid
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Re: Epoxy Skimcoat

Post by Reid »

MattGoose,

I would sand the previous coat of epoxy prior to coating again. You need to ensure a mechanical bond.

Not sure how well the varnish will fill imperfections. I guess it depends on the size of the dimple and your level of acceptance.
Good luck!

-Reid
Someone asked me, if I were stranded on a desert island what book would I bring... "How to Build a Boat."
- Steven Wright

MattGoose
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Re: Epoxy Skimcoat

Post by MattGoose »

Reid wrote: Thu Jun 09, 2022 11:07 am MattGoose,

I would sand the previous coat of epoxy prior to coating again. You need to ensure a mechanical bond.

Not sure how well the varnish will fill imperfections. I guess it depends on the size of the dimple and your level of acceptance.
Good luck!

-Reid
Thanks Reid.

Can I just sand the affected areas and skim there again? How much would I need to sand? The hard part is sanding the low areas without bringing the highs all the way down first.

Thanks!

Reid
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Re: Epoxy Skimcoat

Post by Reid »

120 Grit should be fine. Here is the issue, any areas that you re-coat and haven't sanded run the risk of delaminating, especially when doing really thin skim coats.
-Reid
Someone asked me, if I were stranded on a desert island what book would I bring... "How to Build a Boat."
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MattGoose
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Re: Epoxy Skimcoat

Post by MattGoose »

Reid wrote: Thu Jun 09, 2022 11:57 am 120 Grit should be fine. Here is the issue, any areas that you re-coat and haven't sanded run the risk of delaminating, especially when doing really thin skim coats.
-Reid
Got it. The areas that are a problem are pretty localized - the back deck between the seat and storage area, for example. I can sand all of that.

This is really a sand to break up the surface, not a sand to take off appreciable material, correct?

Thanks!

fallguy1000
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Re: Epoxy Skimcoat

Post by fallguy1000 »

Sand it all lightly say 120 grit.

Epoxy dries at a much higher mil thickness than varnish because epoxy does not really dry.

So, expectations for varnish are 1-1.5 mil and epoxy applied at a rate of 2 oz per sqyd will end up at about 2.5 mil, but when it starts to kick; you probably have some areas that are very thick and need to sand down because kicking epoxy does not lay down..while you sand; you'll know if any areas are real rough; they are probably also high relative to ideal work..
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bklake
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Re: Epoxy Skimcoat

Post by bklake »

I finished my CLC Chesapeake 17LT 20 years ago. Man time flies. Mostly bright except for a white bottom so it doesn't look like a floating log should I need to be rescued. I did the recommended 3 coats of epoxy and tried to do my best not to leave any holidays. I think I found a few by lightly sanding between coats. Any low spot will be shiny. Take a look at the low spots. If the weave of the glass is showing add another coat to the area and blend it in with sanding. Otherwise leave it alone but blend it a little. Epoxy does not go on thin, there is a certain thickness you have to get it to or it looks like crap. Too thick and it starts to run, especially MAS Epoxy.

I used traditional varnish and sanded between coats. It got smoother and more even as I got to the last coat. The traditional varnish usually lasted 2 seasons and wore through quickly where my paddle rubbed it. Next I used some Interlux 1 part polyurethane varnish that lasted 10 years and wore like iron. Sadly, they don't make it any more. Probably didn't sell a lot of it because it lasted so long. I need to recoat it soon, it's on my to-do list this summer. I'm going to try some Total Boat water based stuff this time.

The short answer is that yes, the varnish will fill any low spots if you lightly sand between coats. Almost nobody but you will see the flaws. You will have the chance to improve the finish as time goes on. Or you could just enjoy the kayak and go paddle.
Last edited by bklake on Fri Jun 10, 2022 9:50 am, edited 1 time in total.

bklake
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Re: Epoxy Skimcoat

Post by bklake »

Now that I have some time to remember how I finished it. I think I remember the following:

First epoxy coat, used 80 or 120 grit to lightly knock down the brush marks and bumps. Do not get into the weave of the glass. It is easy to tell if you are hitting the glass because it turns whiter.

Second epoxy coat, used 120 grit and tried to get a smoother more uniform surface. I could still see the weave so didn't sand aggressively.

Third coat, I think I used 180 grit and it came out pretty smooth. I might have wet sanded it.

For tools, I used a DeWalt random orbital sander on the big parts and a rubber sanding block on the sharper edges.

You will not get every dip and low spot on each coat of epoxy or varnish. Sand out the high spots and eventually the low spots will fill in. You have a lot of coats of varnish ahead of you so baby steps. Try to make it a little smoother with each coat. You can't fix a blemish in one coat. I'm pretty sure I used 220 grit between coats of varnish.

fallguy1000
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Re: Epoxy Skimcoat

Post by fallguy1000 »

Two part finishes are way harder.
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MattGoose
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Re: Epoxy Skimcoat

Post by MattGoose »

bklake wrote: Thu Jun 09, 2022 10:55 pm Now that I have some time to remember how I finished it. I think I remember the following:

First epoxy coat, used 80 or 120 grit to lightly knock down the brush marks and bumps. Do not get into the weave of the glass. It is easy to tell if you are hitting the glass because it turns whiter.

Second epoxy coat, used 120 grit and tried to get a smoother more uniform surface. I could still see the weave so didn't sand aggressively.

Third coat, I think I used 180 grit and it came out pretty smooth. I might have wet sanded it.

For tools, I used a DeWalt random orbital sander on the big parts and a rubber sanding block on the sharper edges.

You will not get every dip and low spot on each coat of epoxy or varnish. Sand out the high spots and eventually the low spots will fill in. You have a lot of coats of varnish ahead of you so baby steps. Try to make it a little smoother with each coat. You can't fix a blemish in one coat. I'm pretty sure I used 220 grit between coats of varnish.
It had been too long since I put down some epoxy and it's all coming back now!

I decided to go ahead and sand the whole thing and it's looking much better now. The previous coat I had done when it was too cold (somehow after a 10 month lay off, I had to do it that night!) was super wonky and this one is making it look a whole lot better, and what you said about filling the lows makes a lot of sense.

I'm going to ignore the coat I did cold and chalk it up to experience. Probably one more coat after I finish sanding this one.

Thank you!!

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