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protective sandable coating over plywood


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#1 Sailandbail

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Posted 14 November 2012 - 06:53 PM

I usually use west 206 hardener and apply two rolled and tipped coats on plywood surfaces sand,prime and paint. I try to wipe off the ambian blush off before sanding. I've had a hard time sanding due to excessive plugging. A friend recommended using a additive to thicken the epoxy and make it sand better. I'm guessing he meant 407 or 410? He said to mix it about like the consistency of sour cream and apply it with a squeegee. Please advise.
Thanks

#2 _Vegas_

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Posted 14 November 2012 - 07:07 PM

What is your end usage for this plywood panel? If moisture resistance is important, I would not use fairing compounds like 407 or 410 for this application.

If sanding is hard, perhaps you are sanding too soon after application - the 206 is the slow hardener , and in temperatures below 60 it takes a couple of days to cure to a sandable state. If you can dent the surface of the material left in your mixing cup with your thumbnail, its not ready for sanding ...but it is still chemically active and you can bond right to it with no surface prep.

#3 Rasputin22

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Posted 14 November 2012 - 07:32 PM

A common mistake is to try and put the epoxy first coat on too thick. Over plywood it is best to mix the resin and hardener thoroughly and then use a plastic spreader/squeegee to force it into the grain well. Don't let it puddle and squeegee almost dry and it goes a lot further. When it hardens then the raised grain and fuzz will sand quite evenly without loading up the paper if cured completely. Then the next coat you can float on thicker and build up the protective layer. Then reddish brown phenolic microballoons can be added to the 3rd coat to hide the grain especially on doug fir and I like using a softpad to level it all out. Squeegee another clear coat over the microballoons after sanding to fill pinholes and your ready to prime and paint.

#4 _Vegas_

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Posted 14 November 2012 - 07:49 PM

A common mistake is to try and put the epoxy first coat on too thick. Over plywood it is best to mix the resin and hardener thoroughly and then use a plastic spreader/squeegee to force it into the grain well. Don't let it puddle and squeegee almost dry and it goes a lot further. When it hardens then the raised grain and fuzz will sand quite evenly without loading up the paper if cured completely. Then the next coat you can float on thicker and build up the protective layer. Then reddish brown phenolic microballoons can be added to the 3rd coat to hide the grain especially on doug fir and I like using a softpad to level it all out. Squeegee another clear coat over the microballoons after sanding to fill pinholes and your ready to prime and paint.


Correction to "I would not use fairing compounds like 407 or 410 for this application." as a first coat if moisture exclusion is desired.

+1M to what Rasputin says

#5 casc27

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Posted 14 November 2012 - 07:51 PM

It sounds like you are sanding when the resin is too green, as Vegas mentioned. My usual routine is to put several coats on wet on wet (so no sanding in between) and then wait several days or more before final sanding prior to whatever top coat will be applied. The extra cure time (along with a good water wash to get rid of the blush) really reduces the clogging problem.

#6 mad

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Posted 14 November 2012 - 10:44 PM

Don't waste time sanding undercured epoxy. Just cure it properly (dry heat) and it'll save you time and grief.

Vegas, there's been a heap of these posts/threads lately. Always the same, amine blush, sticky, brittle etc ...???

Does anybody read the instructions anymore?

#7 casc27

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Posted 15 November 2012 - 12:53 AM

"...read the instructions anymore"? Did anybody ever read the instructions??

#8 Ishmael

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Posted 15 November 2012 - 02:15 AM

"...read the instructions anymore"? Did anybody ever read the instructions??


Only to find out why it didn't work right.

#9 _Vegas_

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Posted 15 November 2012 - 02:19 AM

Don't waste time sanding undercured epoxy. Just cure it properly (dry heat) and it'll save you time and grief.

Vegas, there's been a heap of these posts/threads lately. Always the same, amine blush, sticky, brittle etc ...???

Does anybody read the instructions anymore?


Just wait until next month - The "my epoxy didn't cure at 40F in the my New Jersey garage" posts will start up again ...

#10 Sailandbail

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Posted 15 November 2012 - 02:43 AM

Apply second and subsequent coats of epoxy following the same procedures. Make sure the previous coat has cured firmly enough to support the weight of the next coat. To avoid sanding between coats, apply all of the coats in the same day. See Special preparation-Cured epoxy. After the final coat has cured overnight, wash and sand it to prepare for the final finish.

The directions say over night as said above.





Don't waste time sanding undercured epoxy. Just cure it properly (dry heat) and it'll save you time and grief.

Vegas, there's been a heap of these posts/threads lately. Always the same, amine blush, sticky, brittle etc ...???

Does anybody read the instructions anymore?



#11 casc27

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Posted 15 November 2012 - 08:28 PM

Sailandbail, sometimes overnight is not long enough, especially in cooler temps. I've found a few days where the daytime high exceeded 60 F works well. Or sometimes I just put the piece in the sun and let it cook for a few hours and then sand the next day. Interstingly, keeping the piece cool while sanding seems to help so clean, sharp, quality paper and low pressure while sanding in the shade produces the best results for me.

#12 Rasputin22

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Posted 15 November 2012 - 08:47 PM

A little trick that is opposite of what a lot of people try to do. I've coated wood panels with WEST and thought it would help to take them out in the sun to promote a faster cure. When the wood gets heatedup it starts gassing off and makes bubbles and pinholes in the epoxy coating, the last thing that you want. Best to heat the ply up ahead and then bring into a cooler environment to coat and as it cools it will suck epoxy into the wood for better penetration. After it kicks then you can put back out into the sun for post cure.
I learned this from a great boatbuilder and storyteller, Robb White. You can read excerpts from his wonderful book 'How to Build a Tin Canoe' here,

http://www.robbwhite.com/

He hated mixing his woodworking with epoxy work, (me too!) and would dry fit sometimes a whole boat in his basement workshop. He liked using tacks, brads, wire ties, hot melt, to tab parts together and then would turn the furnace on full blast and close the windows and doors and pre-heat the whole assembly. Let it get as hot as he could and then step outside and mix his epoxy and then turn off the heat and go in and brush, roll, spread whatever the whole thing and as it cooled it would soak all the epoxy into the wood, ply, joints and amalgamate the whole boat.

Buy his book, or better yet get the narrated set of CD's, his panhandle drawl and storytelling prowess is a treat!

http://www.amazon.co...s/dp/1401300278

How this south Georgia/Florida cracker got to be the darling of the New England Wooden Boat Magazine set is a wonder as well.

#13 olaf hart

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Posted 15 November 2012 - 10:42 PM

A little trick that is opposite of what a lot of people try to do. I've coated wood panels with WEST and thought it would help to take them out in the sun to promote a faster cure. When the wood gets heatedup it starts gassing off and makes bubbles and pinholes in the epoxy coating, the last thing that you want. Best to heat the ply up ahead and then bring into a cooler environment to coat and as it cools it will suck epoxy into the wood for better penetration. After it kicks then you can put back out into the sun for post cure.
I learned this from a great boatbuilder and storyteller, Robb White. You can read excerpts from his wonderful book 'How to Build a Tin Canoe' here,

http://www.robbwhite.com/

He hated mixing his woodworking with epoxy work, (me too!) and would dry fit sometimes a whole boat in his basement workshop. He liked using tacks, brads, wire ties, hot melt, to tab parts together and then would turn the furnace on full blast and close the windows and doors and pre-heat the whole assembly. Let it get as hot as he could and then step outside and mix his epoxy and then turn off the heat and go in and brush, roll, spread whatever the whole thing and as it cooled it would soak all the epoxy into the wood, ply, joints and amalgamate the whole boat.

Buy his book, or better yet get the narrated set of CD's, his panhandle drawl and storytelling prowess is a treat!

http://www.amazon.com/How-Build-Tin-Canoe-Confessions/dp/1401300278

How this south Georgia/Florida cracker got to be the darling of the New England Wooden Boat Magazine set is a wonder as well.


I use this trick too, preheat then epoxy.
I never sand epoxy, I use sharp cabinet scrapers.
Sometimes I assemble and glue the whole shell using epoxy glues, then epoxy seal the rest of the ply.

#14 Jim Conlin

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Posted 16 November 2012 - 01:54 AM

There's another wonderful book of Robb White stories, titled Flotsam and Jetsam. Publish posthumously.

#15 cyclone

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Posted 16 November 2012 - 02:38 AM

+1 for cabinet scrapers and epoxy, another Robb White maxim.

#16 Mr. Fixit's brother,, Mr. Fixit

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Posted 16 November 2012 - 04:47 AM

I like the autocorrect from OP,,, the ambian blush...

#17 eliboat

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Posted 16 November 2012 - 12:53 PM

Yup cabinet scraper. Sanding is for chumps. Learned this trick onmy first boatbuilding job when I had to coat many sheets of ply and then have them coated, smooth and ready as a surface for LPU paint.




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