How to not waste epoxy....

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tech_support
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How to not waste epoxy....

Post by tech_support » Mon Sep 18, 2006 3:16 pm

Get more mileage from your epoxy!

Most builders, especially first timers, use much more epoxy than necessary. When calculating the quantity of epoxy in a Bill of Material (BOM) we include the amount needed to coat the wood, wet out the glass, make glue, fillets, and fairing paste. We then we add 15% waste factor.

The leading culprits for epoxy waste are:

1) Excessive fillet size. Follow your plans when its comes to fillet size. In almost every case first time builders make their fillets twice as large as needed.
2) Coating wood using brushes. Using a tight foam roller, you can get multiple thin and even coats of epoxy on your plywood. This method uses less epoxy overall verses sloping on one or two heavy coats with a chip brush. Brushing on heavy coats will result in excess build up in some area, and not enough in others.
3) Mixing too much at a time. Try to use all the epoxy you mix. Keep a mental note of any small areas which need epoxy so you do not leave excess in your cup. For example; if you mix up a batch of epoxy to coat your wood, and there is some left over, mix in some wood flour and make glue for butt blocks.
4) Wetting out fiberglass. A good laminator can achieve a glass/resin of 50/50 by weight. We do not assume everyone will be able to get this ratio the first time, however we do assume you will get close. Once the glass is wet and air is removed (using rollers and/or squeegees) any additional epoxy does not add to strength, quite the opposite. Use a slurry of epoxy and fillers to fill the weave of the glass as opposed to using straight (expensive epoxy)



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Post by Knottybuoyz » Mon Sep 18, 2006 5:05 pm

Sounds like good advice coming from a man who's wasted a fair amount of epoxy in his time! :P

So, excuse me if I sound dumb but, here's the scenario. You've got say hmmm? 10' of fillet to make & tape. Ideally you want to work wet on wet right? So step 1 would be to coat the ply with a thin layer of epoxy, step 2 make the fillet from the epoxy filler you just mixed up, step 3 lay in the biax tape and wet it out. Is that how it would go? Is 10' of fillet & tape manageable in the normal working time for a single batch of epoxy & filler, or would you prepare the coating epoxy, filler and taping epoxy in separate batches? Can you mix up the filler in advance and keep it in the fridge? Could you do say 20' or 30' of fillet in one session or would that be too much?

I suppose as you get some experience with the materials you'll be able to do more and more in a single session. I'm thinking the early filleting sessions will prove a little more expensive with a few more wasted materials but sometimes that's the price you pay for experience.

Rick
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"It's not the boat "you built" until you've sworn at it, bled on it, sweated over it, cried beside it and then threatened to haul the POS outside and burn it!"

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Post by chrisobee » Mon Sep 18, 2006 6:04 pm

Pot life is the limit here. The larger the batch of epoxy the more likely it will pop off. I would not try to store mixed epoxy. Your mix it you use it. Outside temp and the temp of your epoxy and the speed of your hardener are all important variables in the amount of time you have to work. Just mixing a large quantity of wood flour takes a significant amount of time. I don't think that you will be getting into the 10 ` plus range without help.

Wet on wet is of course somewhat subjective. Everything should be tacky and pliable but not wet. You need to let things setup a bit. Thus you tend to pre-coat around 10' of seam with one batch, fillet with the next batch, layout tape with the next batch.

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Post by Michael_L » Mon Sep 18, 2006 7:19 pm

A second to what's written above. A high humidity and temp. area like I live in is a big factor in mixing up epoxy batches. My epoxy has an average pot life of 10-15 minutes in the summer - with a SLOW hardner. But I quickly learned a long time ago, if the surface area of the pot is larger, you can significantly extend the pot life. I sometimes use (especially in summer times) a cheap 99 cent plastic paint tray liner. Large surface area, and after left over epoxy cures, if snaps right out and I use the tray again. As for the wet on wet, i've tried it and screw up way too many times for whatever reason - glass gets crooked, gets tacky too son. wet epoxy on dry glass is best. Just my two cents.
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Post by Knottybuoyz » Mon Sep 18, 2006 7:35 pm

Thanks for the tips fella's. I'll try all the things you've suggested. I'm still a little concerned about doing very large areas such as the hull of the TW28. Even doing 1 large panel at a time it can be as much as 10 square yards. That's a heck of a lot of epoxy to mix and wet out 1708 at one time. Anywho, I gotta get a few smaller projects under my belt before I start worrying about that I guess.

Rick
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Post by chrisobee » Mon Sep 18, 2006 8:22 pm

If you are going to be doing a TW project. you may as well realize that in many spots its going to be a multi-person project.

When you work on a big panel one person mixes while the other works the panel.

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Post by Knottybuoyz » Mon Sep 18, 2006 9:11 pm

Hey Chrisobee

Yer right. I figure if I offer 'nuff beer & pizza (w/back bacon) on here a whole bunch o' you guys will show up for those major milestones! *lol*

Mini-workshop is almost done. Should start a small project next summer. Thinking of the V10 will make a nice tender for the TW28!

Rick
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"It's not the boat "you built" until you've sworn at it, bled on it, sweated over it, cried beside it and then threatened to haul the POS outside and burn it!"

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Post by jeremy » Tue Sep 19, 2006 1:22 am

Knottybuoyz wrote:Thanks for the tips fella's. I'll try all the things you've suggested. I'm still a little concerned about doing very large areas such as the hull of the TW28. Even doing 1 large panel at a time it can be as much as 10 square yards. That's a heck of a lot of epoxy to mix and wet out 1708 at one time. Anywho, I gotta get a few smaller projects under my belt before I start worrying about that I guess.

Rick
Don't forget also that epoxy goes off much, much faster in the pot than when spread out over a large area.

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Post by Robertk » Tue Sep 19, 2006 7:55 pm

Several people working together has worked best for me. If you have help that understands the method and wants to work as a team it becomes a very efficient process. Start with the glass tape cut to manageable lengths and make a plastic covered tray out of plywood with 3/4" sides. It should be about a foot or more wide and at least 4' long. This is where the FG tape will be wet out with a squeegee. While one does this another puts a "primer" coat on the wood. The third mixes some of the epoxy up with wood flour/fumed silica and starts the fillets using the same tray and broad knife a drywall finisher uses. The wet out tapes are placed and squeegeed down with the excess spread out on the floor and sides. Other tasks are the same . One does a task and the others work with him to get the job done. There is little time for epoxy to set up prematurely. My D 15 was built this way in a few hours one weekend.

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Post by Robertk » Tue Sep 19, 2006 8:01 pm

It was a few hours i.e. about 5 on Saturday and 5 on Sunday. That was for the bare hull only.

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