New material: epoxy

[Well, not new, just new to me]
Now we've all used epoxy sometime in our lives. at least to glue something back together. I've done that many times, but I never used liquid epoxy until today, when I came to the part of my door-restoration project where I sealed the outside of the door with marine epoxy. My experiences with this substance follow. Long post, be warned.
Just for background, the project is re-facing a beautiful Craftsman door whose plywood skin had started to delaminate badly. The door is a big (42") door with nine beveled lites of various sizes, and was at one time very nicely covered in oak-veneer plywood. The original plan was to try to restore the veneer on the face. After doing a partial repair a couple years ago where I reglued just the top layer of veneer, I determined that this was beyond my capabilities and started asking around at local shops. To make a long story short, the answers I got were either "can't do it" (would have to replace all the glass with safety glass to bring it up to code, etc.), or the job was prohibitively expen$ive.
So we decided I'd just reface the door, restore the top surface and make it smooth and level, and paint it. Keep the old Craftsman design, just lose the natural wood facing. So I peeled off about half of the old plywood (mainly from the bottom half of the door), cleaned up the surface, and glued on new 1/4" marine plywood (HydroTech). Also pieced in some of the old oak veneer I had left over in places where only the top layer had let go, leaving a solid substrate. This left lots of discontinuities and gaps, since the plywood I used wasn't exactly the same thickness (and in some cases had been glued over the bottom layer of old veneer which was still well bonded). So I filled these in by gooping on lots of PC-Woody (basically a wood-epoxy paste).
Today I arrived to smooth down the surface and seal it. Sanded it smooth, mixed up the epoxy and went to town. First time I'd ever used this stuff; I ended up getting West System 105, and their slow-setting 206 hardener, on the suggestion of the people at the local West Marine. (Turns out West System is from a different company.)
It went on easily, and was much less nerve-wracking than I'd expected. (I always get anxious around *anything* that sets, hardens, catalyzes, gels, or otherwise changes state. A tube of caulk can cause heart arrhythmia.) It basically went on like fairly thick varnish. Soaked into the wood surfaces nicely.
I chose the slow hardener because I knew it would be hot this week. Today it was close to 90° in Berkeley where I was working. I thought it would be better to risk a long set time (the back of the can says 10-15 hours for "cure to solid") than to risk having the stuff harden up while I was still trying to brush it on. Turns out I made the right choice.
I mixed up what I thought would be enough plus a little more (another anxiety-producing dilemma: too much or not enough?). Better to err on the side of wasting some rather than running out before covering the surface, thinks I. About half-filled the plastic mixing cup I bought. I got it all on in about 10-12 minutes, with the epoxy still liquid, when I noticed that the bottom of the cup was getting warm. *Very* warm.
Now they warn you that the stuff is exothermic: "Curing epoxy generates heat. When contained, a large mass of curing epoxy has a very short life, and can generate enough heat to melt plastic and foam, burn your skin and ignite combustible materials".
It's just very strange that this reaction happened well after I mixed the batch, and after I'd used most of it. The cup got very hot, and I noticed the material was actually smoking a little, and gelling up. It all happened very quickly. Fortunately, I was just about done; I just mixed up a smaller batch in another cup and finished up. By the time I was finished brushing on the second batch, there as a big solid lump in the first cup.
So apparently this stuff behaves differently from most other setting materials: the more stuff there is (large mixed batch or thick coat), the faster it sets up. In my case, it was just about perfect. I was worried that I'd have to hang out at my friend's house way past sunset with a sticky front door; it set hard to the touch in just a couple hours.
The West System stuff is pretty cool, if expensive; I bought the pumps they sell which are made to go into their cans. Just pump the same number of strokes of resin and hardener, and you get a perfect mix. No measuring. (I'm guessing that other brands must use this system too.)
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David Nebenzahl wrote:

<snip>
Right, sort of. (Ditto for polyester resin.) A thick coat won't make much difference but a deep container will. The solution is to mix what you need then pour it into a shallow container so it is only 1/2" or less deep.
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On 10/13/2010 1:12 AM, David Nebenzahl wrote:

like you describe which can be cured rapidly (or slowly) to solids requiring long, high temperature cure.
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different systems use different ratios. I use small 1 oz.measuring cups,you can buy them at hobby stores or at Wal-Mart in the Pharmacy section. They are marked in fractions of an oz,drams,and mL. you also can use the oral syringes for measuring small amounts. use separate syringes for resin and hardener,and mark them clearly.

Here's a tip; go to System Three's website,and download their Epoxy Book. It's free. It's got a lot of good info about epoxies and their use. They also have a Trial Kit that is a good deal.
IIRC,it's www.systemthree.com
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Save yourself some money next time and try uscomposites. West System is just a high priced label. None of the companies actually manufacture the raw components. Big chemical companies like dupont make it. West, etc just resell. And West is sort of like Bose, you're paying for the label as well as the product.
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wrote:

one trick is to mix in a tray instead of a cup or bowl. the wider,shallow tray keeps the epoxy mass from heating up too fast.

West,System Three and RAKA are good,boat-building type epoxies. I use RAKA because they had the best price for the 1.5qt "kit". I use West fillers(fumed silica,microballoons,wood flour,chopped plastic fiber,chopped glass fiber) because they are available at a local boating supply store.(along with glass cloth)
you can get measuring cups at HD or Lowes,in the paint section. for small jobs,Wal-Mart Pharmacy or hobby shops,1 oz cups,marked in fractions,mL,drams,Tblsp. or use oral syringes.
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6 quart 2:1 kit at raka = $93. Same 6 quarts of 2:1 at uscomposites $69. Clostest west pirce is around $140. Like I said before none of them actually manufacture the stuff. They are all packagers.
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Is it UV resistant and stable so it wont degrade in a few years, I dont think so, I dont believe its meant as a top coat.
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On 10/13/2010 7:34 AM ransley spake thus:

Don't worry your pretty little head about that, Mr. Can't Be Bothered to Use Apostrophes. It's not being used as a topcoat: I'm going to prime and paint over it, so UV resistance isn't an issue. (Besides, epoxy is more UV resistant than most varnishes.)
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WTF asshole, whats this apsotrophe crap, and no epoxy is not UV stabile compared to marine varnishes, and of course on doors thats all you should ever use, but you knew that.
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Bondo would have been quicker, easier, cheaper. Yes it hold up on doors.
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On Wed, 13 Oct 2010 11:44:27 -0700 (PDT), ransley

moisture). If not properly sealed it will pop if the moisture gets in and freezes. I've used bondo on wood - won't use it again.
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On Oct 13, 4:41 pm, snipped-for-privacy@snyder.on.ca wrote:

so much this. I don't even like Bondo on cars, unless it is used exactly according to directions (most people don't read 'em) - only as a skim coat over top of good solid metal. If there are any holes in the panel from a dent puller etc. or rust repair, they should either be welded shut w/ a copper backing or else backside of panel must be painted w/ good pref. epoxy paint after bondo sets up and then pref. undercoated over top of that. Any other approach is doomed to failure. DOOOOOOOOOOMED.
I believe the main reason that it is hygroscopic is not that it is polyester based but that the filler is mainly talc.
nate
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wrote:

fiberglass bonded with polyester resin absorbs water - while most epoxy bonded fiberglass does not.
Nylon also absorbs water. Polyethelene does not.
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On Wed, 13 Oct 2010 07:34:42 -0700 (PDT), ransley

marine spar varnish. (for extra UV protection)
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re: "One thing I don't like is the pumps. Can't always tell whether they're primed..."
I won't disagree with the use of a scale, but as far as priming the pumps...
I prime the pumps into separate cups and once I'm satisfied that they are primed, I set the "priming cups" aside and mix the ingredients in the tray/cup from which I'll use the epoxy.
Once I'm done with the epoxy for the day/session, I pour the stuff from the "priming cups" back into their respective cans.
Everything else you've said about half-strokes and the mess is absolutely true. I really should get a scale. ;-)
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re: "The cup got very hot"
It's kind of fun to watch a cup melt and deform as the stuff heats up. BTDT
re: "another anxiety-producing dilemma: too much or not enough?"
The real dilemma is: Can I mix just enough to get it all used up before it gets unworkable, so there is no waste? That's an art.
A fun tip:
If you need to keep epoxy from sticking to something, coat the something with vaseline.
I've made molds by coating objects with vaseline, wrapping it with epoxy/fiberglass and then sliding the object out.
I've made tunnels through thick masses of epoxy/fiberglass by coating dowels with vaseline and then pulling them out once it's cured. You get a nice neat tunnel with no drilling required.
I drilled 3/4" holes halfway through a board, dropped nuts into the holes and inserted vaseline coated bolts through the top of the board to hold the nut in place. I then poured epoxy around the nut to seal it into the board, sanded it and painted it. The nuts were permanently embedded (and hidden) in the wood and I could bolt and unbolt objects as I needed.
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On Wed, 13 Oct 2010 12:37:04 -0700 (PDT), DerbyDad03

Paste wax works every bit as well, and it won't "pollute" the epoxy. Vaseline can retard or weaken the resin - not positive about epoxy - but definitely not good with Polyester.

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On 10/13/2010 1:44 PM snipped-for-privacy@snyder.on.ca spake thus:

This actually came into play as well; as I had to reattach the door hardware so my friend could actually use it, I was worried about the handle sticking to the epoxy (even though it seemed solid, I wasn't positive it was completely cured), so I attached it with pieces of waxed paper between it and the door.
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