Epoxy 2nd coat question?

I just finished applying the first coat of epoxy over the glass on the bottom of my NE Dory.  I read on MAS epoxy website that one can apply the 2nd coat up to 11 hours after the first without sanding.  I also read on CLC where John states a 2nd coast can be applied within 30 hours, thereafter a light sanding is required.  So is there that much leaway, or should i just wait, trim the overhanging glass and light sand tomorrow?

Also, if I decide to just wait, what is the recommended sandpaper number?  I guess I am just trying to scruff it up a bit, is that correct?  Is there any performance or longevity difference between re-coating soon after the first or waiting?


21 replies:

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RE: Epoxy 2nd coat question?

   Well, i originally did a search on the website and didn't come up with any similar questions/responses.  Then I did a similar search on google and found a bunch of similar queries all on CLC forum...go figure.  So if I read them correctly, 24 hours is about the max and otherwise a 80 or 120 grit scruffing is needed and there is no difference in performance between a mechanical bond and a chemical bond with modern epoxies.  So do i have the info correct or does anyone have any other opinions?  BTW thanks guys in advance....

RE: Epoxy 2nd coat question?

The 2nd coat within 24 hours worked for me on my Peeler Skiff. I used 80 and 120 grit for scuffing when I did need to.. Didn't see any difference in the results. Just make sure you don't cut too deep if you use 80 grit. You dont want to get down into the glass fiber.

Cheers,

Dick

RE: Epoxy 2nd coat question?

Check the manufacturer's data sheet. System Three says 3 days before sanding is needed, for example.

Have fun,

Laszlo

 

RE: Epoxy 2nd coat question?

I used 80 grit between coats, each coat was about 20 hours apart. It was during the coldest part of the winter and my garage was only in the low 50's F. It worked fine. As I mentioned in another thread, I used mainly a hand sander. The power sander works fine but you cant get into corners, they are very noisy and the paper for them is 3x the cost.

   

RE: Epoxy 2nd coat question?

Wow!  Maybe I'm way out of line here, but my understanding was not that we were scuffing for adhesion, but rather were smoothing for a fine finish.  Thus, while you can pile on a second coat on in a relatively short time, piling more epoxy on a wavy surface only makes it wavier.  At least with my boat, sanding caused the surface to change color.  Where it was high it turned white and between these "summits" the epoxy remained clear.  My objective was to get the entire structure to a uniform grey-white condition with few, if any, spots in between.  The more like that I could make everything -- regardless of the coat number -- the nicer the finish.  Again, maybe I missed something, but I wasn't scuffing for adhesion.   

RE: Epoxy 2nd coat question?

   Applied the 2nd coat all over the glass on bottom of the hull and what would be the 1st coat over the unglassed wood and even though I was super careful there are some waves and a few bubbles.  As noted in the post by MountainSailor, I will wait a bit to sand for the next coat so that I can get a more uniform finish.  Any suggestions on how to get a really smooth finish?

 

RE: Epoxy 2nd coat question?

   BTW, the hull is going to be painted.....

RE: Epoxy 2nd coat question?

Oceanluvr,

I followed the instructions in the CLC Tips for Boatbuilders and they worked well for me. Brightsides can be polished using buffing compound and an automotive buffer, leaving the exterior of my Peeler Skiff looking like gelcoat. In retrospect, I would not again use PreKote. It's just too soft and susceptible to ambient moisture before it gets covered by paint. Brightsides sticks very well to epoxy, which is much harder than PreKote.

One key to a good finish is good surface prep. When you're going to paint, you have the latitude to use fillers like marine bondo to help get a smooth, fair surface to paint on.

Cheers,

Dick

RE: Epoxy 2nd coat question?

   Thanks Dick, I admired the paint job on your skiff, as I recall before deciding to paint my dory.  Good tip on the buffing compound and the elimination of the PreKote.

 

RE: Epoxy 2nd coat question?

Regarding how to get a really good finish, I think there are two good answers to that question:  First, sand, sand, and sand.  And second, sand some more.  On my first coat of epoxy I wasn't too particular about how it went on.  I experimented with brushes and spatulas and a mix of the two and only later discovered that I'd covered everything really well, but also I had created some inconsistencies in the application that only considerable amounts of sanding could fix.  (And as you know, sanding epoxy is not fun.)  After a lot of trial and error I now use a fine foam roller to apply and work in really small amounts of epoxy.  Then I tip that out with the roller when the epoxy is tacky.  This reduces sanding time and gives me a nice, even finish.

Painting your hull -- as opposed to varnishing it -- tends to magnify minute imperfections in your work (sanding, etc.) so get it right before your start that process.  I'm well pleased with the gelcoat-like finish on my boat, but there were many hours invested in achieving it.

 

 I used the primer too and it has its virtues, but it is not easy to work with and I can't comment on whether it made a difference or not.

 

I hope this helps.  

RE: Epoxy 2nd coat question?

OceanLuvr,

I second MountainSailor's sanding, sanding, sanding...

It's also important to get your sanding technique down. I used an orbital sander connected to a HEPA-filtered dust vacuum for most of it. Long, even strokes, and use a bare hand to judge smoothness and a bright light to help judge fairness. Fortunately, you'll get lots of practice.

You might also consider that dark colors will show imperfections more than lighter colors once things are polished up and dark colors put more thermal stress on the underlying epoxy in the summer sun.

Cheers,

Dick

RE: Epoxy 2nd coat question?

   How many times does it take to sand through one layer of cloth, just woundering? Everyone here agrees to sand,sand and sand somemore. Bad choice in my view with little cloth on your surface. Try Peel-ply, you'll learn some-thing. Avoid your problems with saging resins, too dry, and all your air pockets. If you master this, you'll have less sanding, and Epoxy costs. Note; you can use Peel-ply for resin filling in after your first sanding. Give it a try, I hate to sand.

Someone teaching these classes on building these boats had better get experts in and teach some new skills in Composites. I watched the video on the ch17 kayak, and ROTFLOL watching him apply the cloth and resin. What a joke, but I do LOVE YOUR BOATS.

 

RE: Epoxy 2nd coat question?

   Dick: I am going to go with a light off white hull color as I am in Florida and the sun is brutal on dark hulls.

Happy Hooker:  I have peel ply but have not used it as I read that it is really good only on the flat surfaces, and that if not used correctly, meaning no voids or air spaces one can create a bigger problem.  Have you used in on sides or curved areas of your hulls?  Any tips you can share?

 

RE: Epoxy 2nd coat question?

   Cut the peel-ply any size you need to fit your curves, over lap onto it self as needed. There are many differant kinds of ply in the market. Some are very thin and easy to shape. Some brands are very heavy weight and don't fit in convex or compound shapes too well. Try small pieces - then go big if all is well.

RE: Epoxy 2nd coat question?

 Thanks to all who responded.   Is it necessary after the first coat of epoxy to sand smooth all of the minor sags or will the next coat if applied more carefully even it out?  I have been know to be obsessive at times and don't want to go overboard trying to get a perfectly smooth finish on the first coat.  

RE: Epoxy 2nd coat question?

   Watch these videos on peel-ply, then give it a try. It's not hard to do.

https://www.youtube.com/watch?v=raxYTCIkD54&list=PLVWnERGbVWT4Q_x08EniIa-B9v8oGuoiY&index=14

 

https://www.youtube.com/watch?v=R2M1sHf_B9c&index=16&list=PLVWnERGbVWT4Q_x08EniIa-B9v8oGuoiY

 

https://www.youtube.com/watch?v=MQ3O0o_MQ6o&index=17&list=PLVWnERGbVWT4Q_x08EniIa-B9v8oGuoiY

 

https://www.youtube.com/watch?v=UvgNYS5dVo4&list=PLVWnERGbVWT4Q_x08EniIa-B9v8oGuoiY&index=15

 

https://www.youtube.com/watch?v=3cTrKlzK0rw&t=62s

 

https://www.youtube.com/watch?v=8-JVVTPQeJE&t=204s

 

RE: Epoxy 2nd coat question?

   Now go big...

 

https://www.youtube.com/watch?v=P4f43Xl6Zt0

RE: Epoxy 2nd coat question?

Thanks, Happy Hooker...amazing what one can learn from the internet and staying at a Holiday Inn!  :)

Definitely going to try the peel-ply on my next coat.

RE: Epoxy 2nd coat question?

   Hello,

    Being new to epoxy I was under the impression, using Mas Epoxy, that there were no sanding requirements between layers.

    Since I did not sand between coats am I subject to flaking or scaling?

Thanks

RE: Epoxy 2nd coat question?

This is from the MAS Epoxy website - FAQ

What is the recoat time?

Since epoxies from MAS are 100% solid (no solvents), recoat time can be as short as it takes to achieve surface tack. If more than 12 hours passes between coats, do a light scuff sand. Use a cotton ball to test if a light scuff sand is needed. If the epoxy holds the hair of the cotton ball, you can recoat without sanding. If it doesn’t, a light scuff sand will help adhesion between coats. Remember the “Rule of Thumb” test (if you can press your thumbprint in the epoxy, but there’s no tack, then you should do a scuff sand, but will be getting a chemical as well as a mechanical bond.) Remember, warmer conditions make for a faster cure time. Review the chart in FAQ 5 to see an estimated cure schedule for the temperature you’re working at.

RE: Epoxy 2nd coat question?

   Thank you Oceanluvr

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