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Old 06-09-2013, 23:07   #1
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epoxy question from someone who knows EVERYTHING about epoxy

okay... there is very little truth to that statement about my knowing everything about epoxy.

i do a lot of resin / glass work with epoxy and resin with and without glass.

i am soon to put up a 1/8th inch (wood) headliner and dont know how to epoxy the deck side without making it too rigid to conform to the cabin top.

i was painting the deck & cabin top so i pulled all the hardware and filled and faired all the holes and i have mixed up laminating resin with 406 and have covered the entire cabin top (after filling each individual hardware hole).

so... i dont really think i need to epoxy the cabin side of the new headliner but ya just have to be crazy not to...

back to the question... how do you treat wood without stiffening the wood?

-steve
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Old 07-09-2013, 03:05   #2
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Re: epoxy question from someone who knows EVERYTHING about epoxy

Quote:
Originally Posted by ssanzone View Post
okay... there is very little truth to that statement about my knowing everything about epoxy.

i do a lot of resin / glass work with epoxy and resin with and without glass.

i am soon to put up a 1/8th inch (wood) headliner and dont know how to epoxy the deck side without making it too rigid to conform to the cabin top.

i was painting the deck & cabin top so i pulled all the hardware and filled and faired all the holes and i have mixed up laminating resin with 406 and have covered the entire cabin top (after filling each individual hardware hole).

so... i dont really think i need to epoxy the cabin side of the new headliner but ya just have to be crazy not to...

back to the question... how do you treat wood without stiffening the wood?

-steve
There are epoxies for all types of applications all with different characteristics. If you feel you really have to use epoxy, there are several products on the market that would suite your situation. I have used System3 S-1 sealer with excellent results, it will stiffen the wood somewhat, everything will to some extent, but it is thin enough and flexible enough that it shouldn't be a problem.
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Old 07-09-2013, 04:05   #3
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Re: epoxy question from someone who knows EVERYTHING about epoxy

Quote:
Originally Posted by ssanzone View Post
okay... there is very little truth to that statement about my knowing everything about epoxy.

i do a lot of resin / glass work with epoxy and resin with and without glass.

i am soon to put up a 1/8th inch (wood) headliner and dont know how to epoxy the deck side without making it too rigid to conform to the cabin top.

i was painting the deck & cabin top so i pulled all the hardware and filled and faired all the holes and i have mixed up laminating resin with 406 and have covered the entire cabin top (after filling each individual hardware hole).

so... i dont really think i need to epoxy the cabin side of the new headliner but ya just have to be crazy not to...

back to the question... how do you treat wood without stiffening the wood?

-steve
i dont know if this will work that well with 1/8' ply,but if i need a flexible bend in ply,i use a radial arm saw and cut slots in the back side of the ply wood,through the first layer of veneer about 1/4-1/2' apart.

how deep you cut and how far apart will regulate the flexibility and amount of bend,easy to get a 90 degree bend in 3/8 ply.

if you want to keep the ply rigid once you have the required bend,you then fill the slots with epoxy filler mix.
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Old 07-09-2013, 04:13   #4
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Re: epoxy question from someone who knows EVERYTHING about epoxy

Quote:
Originally Posted by ssanzone View Post
so... i dont really think i need to epoxy the cabin side of the new headliner but ya just have to be crazy not to...

back to the question... how do you treat wood without stiffening the wood?

-steve
I can't help with your epoxy question, but I will mention I was faced with the same scenario (with thin ply headlinings). My answer was........paint . And even that I think is actually superfluous given that the bare headlining backs had been up for 40 years without any problems - but I just could not resist doing "something".........."just in case" .
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Old 07-09-2013, 07:37   #5
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Re: epoxy question from someone who knows EVERYTHING about epoxy

Ssanzone--The advice above to use System 3 epoxy is appropriate. As you are probably aware, there are lots of different types of epoxies, and some are more rigid than others. WEST System from the Gougeon Brothers has an elongation of about 4%, which you can compare to polyesters which typically have much shorter elongations, on the order of 1%-2% (they are pretty brittle, and that's why they crack so easily). System 3, on the other hand, has an elongation of 11%, which means it stretches a lot under load. So for your application, you would probably be safe to coat the plywood with System 3, let it cure, and then press it into place. An overhead panel will have a fairly gentle bend and so the blind side surface will not stretch too much. It would be smart, however to do a small test piece first just to make sure.

As for the suggestion of kerfing and back-filling plywood to make it bend to a tight radius, that's one way to do it. However, there is such a thing as "bendy plywood" which has all layer grains running in the same direction, and this makes it bendy in the cross direction. One supplier is Winwood Products, link:

Flexible plywood (bendy plywood & flexiply) :: Winwood Products

I hope that helps.

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Old 07-09-2013, 07:46   #6
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Re: epoxy question from someone who knows EVERYTHING about epoxy

Great thread, reading with interest.
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Old 07-09-2013, 08:04   #7
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Re: epoxy question from someone who knows EVERYTHING about epoxy

My experience has been that a thin film of epoxy doesn't stiffen ply much at all. So long as there's no fiberglass involved, you can coat and bend 1/8" easily.
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Old 07-09-2013, 08:13   #8
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Re: epoxy question from someone who knows EVERYTHING about epoxy

WEST SYSTEM | Specialty Epoxies - G/flex



Bendy ply is generally laminated over due to its weakness. Coat with anything though, this is a non-issue (unless you slop on way too much neat resin). Just seal it up and go.
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Old 07-09-2013, 08:15   #9
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Re: epoxy question from someone who knows EVERYTHING about epoxy

i use penetrating epoxy on things and areas i dont want stiffer, and i use a thicker variety with or without fillers for those items needing the stiffness......
minaret is a good guru of boat repair.....
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Old 07-09-2013, 08:22   #10
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Re: epoxy question from someone who knows EVERYTHING about epoxy

I'm assuming you want to use the epoxy as a sealer, not to structurally bond the plywood to the cabin top. If this is the case then I would recommend using Smiths CPES (clear penetrating epoxy sealer) It is a wonderful product with many uses. I use it professionally as a base to stick awlgrip onto wood or varnish onto teak. It will soak in and seal but remain flexible. If you want the underside of that plywood to last for ever, glue some enamel paint on to it with CPES.

I would also recommend using it on the interior side of the plywood to hold the varnish or paint on it. CPES soaks into the wood but will not fully cure for about 5 to 8 days. Overcoated paint or varnish will cure first, and will then literally be epoxied on to the wood.

I also apply it over stained planks before varnish when restoring wooden runabouts.

The problem with sealing wood with regular epoxy is that when the wood flexes it will crack the coating and allow water in. There have been a lot of boats built with oak frames coated with epoxy, that had the oak rot out inside the epoxy shell.
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Old 07-09-2013, 08:27   #11
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Re: epoxy question from someone who knows EVERYTHING about epoxy

Quote:
Originally Posted by ssanzone View Post
okay... there is very little truth to that statement about my knowing everything about epoxy.

i do a lot of resin / glass work with epoxy and resin with and without glass.

i am soon to put up a 1/8th inch (wood) headliner and dont know how to epoxy the deck side without making it too rigid to conform to the cabin top.

i was painting the deck & cabin top so i pulled all the hardware and filled and faired all the holes and i have mixed up laminating resin with 406 and have covered the entire cabin top (after filling each individual hardware hole).

so... i dont really think i need to epoxy the cabin side of the new headliner but ya just have to be crazy not to...

back to the question... how do you treat wood without stiffening the wood?

-steve
Before you jump to conclusions try a test. Cut a piece of the material you plan on using and coat it with the epoxy you plan to use, put in place to see if it does/doesn't work.

My guess is regardless of the epoxy type, that unless you are adding fiberglass, it won't matter much. +1 for what DOJ said, is epoxy necessary? Many people figure epoxy is the best for some things so it must be great for everything when in fact it is sometimes overkill.

One other thing, if the surface you are conforming to has compound curvature no matter what you do it will be a tough job. Plywood doesn't like to bend in two directions at the same time. There is a plywood boat building method for multihulls called "tortured" plywood which develops great stiffness in the hull by taking advantage of this fact.

Cheers
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Old 07-09-2013, 10:24   #12
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I think you're over thinking this. 1/8" is incredibly flexible and adding a coat of sealer epoxy isnt going to appreciably stiffen it but like a prior post stated just experiment with a little section to see if it behave as you'd like.
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Old 07-09-2013, 11:38   #13
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Re: epoxy question from someone who knows EVERYTHING about epoxy

as always... all great advice.

as you all have guessed, the curve in the cabin top is pretty slight (no more than 4' over an 8' span and that is reduced again because i will be putting the head liner up in 3 panels ((38" X (60" * 3) long X 3)) so i have access to the deck hardware nuts when / if needed (without having to drop the entire liner).

even thou i am going to great lengths to make eliminate the risk of water coming thru the deck i am going to have to reinstall some hardware on the cabin top and we all know water follows the path of least resistance which will be onto the top of my new headliner.

the goal of treating the deck side is just to add some protection from any water that may hit the top of the 1/8".

i have decided on red oak (mostly aesthetic and partially because it is available) and i expect i will spray it with compression varnish. it will be light enough that it balances out how dark the cabin is with all the mahogany but still add a good looking element with the red grain pattern.

the install will be similar to a drop ceiling with mahogany frames (1/4" frame epoxied to to cabin top and 3/8" (with a 1/8" routed off the bottom (into a 'T')) to support / suspend the panels. it will also be attached directly to the cross frames to keep the bend and provide additional support.

-steve

5/8

2/8 = 1/4
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Old 07-09-2013, 12:04   #14
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Re: epoxy question from someone who knows EVERYTHING about epoxy

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Originally Posted by minaret View Post
WEST SYSTEM | Specialty Epoxies - G/flex



Bendy ply is generally laminated over due to its weakness. Coat with anything though, this is a non-issue (unless you slop on way too much neat resin). Just seal it up and go.
Yeah, if I understand the question... you want to know what to coat the back side of your 1/8 ply headliner with? I guess to seal it? Dont know that I've ever seen one sealed, but anything will work. Use that old varnish youve been saving for years... In that environment it'll last forever....
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