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Epoxy Tricks


Howard

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The average back yard builder will do fine with pumps, mostly because they use small quantities of goo, per epoxy session and their shop environment may prevent larger quantity use (too cold or too hot). For me, pumping 30 strokes from each jug, to get a batch for some sheathing isn't practical or accurate. I've had pump issues in the past and use marked containers for small batches and weighed for larger.

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The average back yard builder will do fine with pumps, mostly because they use small quantities of goo, per epoxy session and their shop environment may prevent larger quantity use (too cold or too hot). For me, pumping 30 strokes from each jug, to get a batch for some sheathing isn't practical or accurate. I've had pump issues in the past and use marked containers for small batches and weighed for larger.

Oh man- I would never pump that amount!! :wacko:

 

6 or 8 maybe 10 pumps is about my limit- past that I measure with a marked stick.

 

And as I said in an earlier post- for LARGE jobs, I pre  pour the resin into many containers, so all I have to do is measure in the hardener.

 

DO remember to add the hardener- I forgot once and glassed 6 feet of deck on a 35 foot tri, without- made a HUGE mess :(

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Yep- makes things go much easier. As I said, I used the trick to glass the hull of a Princess 22, by myself, in a shop that was sitting at 104 degrees.

 

Be certain the container is straight sided- a tapered one will give you a bad ratio.

 

I've used pretty good sized tin cans for the purpose. Mix, pour it on and squeegee it out.

 

Even then, best hit the head before you start, cause in hot weather you gotta MOVE.

 

Which brings a story ( maybe from here) of a guy glassing a hull and his pants fell down - belt broke. They fell down, he stepped out of them and finished glassing, a little less dressed :D :D

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I left those crystallized jugs of resin in an 80 deg room for about 3 days and they never started to melt.  Put one in a pot of water on a hot plate around 8:30 AM and by shortly after noon it was all liquid.  The water never boiled; wasn't meant to.  BTW that was cold water on a cold hot plate at 8:30 when I plugged it in.  Pro'bly take much less time if set in pre-heated water. 

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Crystallized goo needs more then a return to room temperature, to melt the crystals back in. I don't know the temperature it needs, but a trip to the micro wave, if in plastic jugs works, or if in metal, placing it in tap water as hot as it comes from the hot water heater (usually about 125 degrees) works too.

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Update on the fillets:

 

I did a few more tests, this time using the same Meranti I'm using to build the Princess, along with larger fillets of various sizes.

 

Bottom line is I pretty much got the same outcome. In almost every case, the failure occurred as the first layer or ply of the bottom or horizontal piece simply peeled up and separated. Going as large as 1 1/4" radius (2 1/2" diameter) fillet tool, only resulted in a larger piece of plywood pulling up. In no case could I get the plywood to break first. (I did get one piece to snap in half, but only by standing on it).

 

The epoxy simply soaked into the surface ply layer to the glue line, where it stopped. The failures were generally at the subsurface glue line. Bottom line is the epoxy is stronger than the peel strength of the plywood it is holding together, so there is a limit to what is necessary as far as the size of fillets is concerned, especially if most of the structural fillets will have tape, as all of mine will have.

 

As time (and as scrap materials accumulate), I might run a similar test and measure the weight or pressure it takes to force these joints to failure, with and without various combinations of tape. General strategy for a heavily loaded joint is a bigger fillet and larger spread and more layers of glass tape. But again, a chain is only as strong as the weakest link. There would be no reason to use three layers of tape if the first one is strong enough to peel the plywood up.

 

Something else to consider, as the industry keeps going where standards are being relaxed or ignored, is to be mindful that the surface layer of plywood is more than just a pretty face. There are structural implications. If they start making the faces so thin you can see through them, there might not be anything left for epoxy to hold on to.

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Glass tapes:

 

For those new to this game, basic tapes are woven (which you buy in a roll, or piece cut from a roll), which have selved edges. While those work to keep them from unraveling, they are left behind, which leaves a bump to fair out on the edge. Curious what experienced builders are using to fair out or eliminate the bump?

 

Also, the woven tapes are generally cut on a 90 degree bias, which on curves, etc. will sometimes result in a pucker. If you have a roll of cloth, it is possible to cut your own strips of tape on a 45 degree bias, and in doing so no only do you eliminate the selved edges, but also the tape will better conform to curved shapes, such as the leading edge of a CB or rudder or outside edge of a curved hard chine.

 

Then there is the long standing question (preference?) of applying the tape wet or dry?

 

Lastly, to help fair the tape, what are folks doing about peel ply? How are you using it and where are you getting it?

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My Princess called for 1208 biax so my fillets needed to be large enough to get a smooth bend. Two layers of tape (which I cut from a large roll)

 

on interior seams over lapping an inch and then just left as is. One layer on the outside also rounded over for a fair chine. After the weave fill

 

I took a long board to the high spots and mixed a thickened goo that a 6 inch drywall trowel feathers out nicely. 

 

 

After my first section put dry onto a wet fillet, I wet all the tape first. Used a shallow tray 4 feet long 6 inches wide. It sucks up a lot

 

of epoxy, but I am confident it will never come apart.

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Lastly, to help fair the tape, what are folks doing about peel ply? How are you using it and where are you getting it?

 

I don't claim to be an experienced builder but I have looked into the peel ply issue and found the following sources:

 

EconoPly:  http://www.peelply.com/index1.html

 

or https://store.airtechintl.com/htm/defaultnetscape.htm

 

Also Jamestown Distributors, at: 

 

http://www.jamestowndistributors.com/userportal/show_product.do?pid=3754&familyName=Vacuum+Bagging+Release+Fabric

 

JD's (online) catalog is a little confusing;  in one place it claims they sell it in rolls but, elsewhere it lists 2 or 3 discreet sq. yard quantities.  I would call them to get clarification.

 

EconoPly appears to be the cheaper and I believe B&B has said that it's the brand they use when they use peel ply and find it satisfactory.

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  • 2 weeks later...

I have the calibrated pumps from Graham but often want to mix odd size batches of resin.  I picked up a small digital platform scale from Amazon for about $15. and have had no problems using a 2-1 weight ratio instead of volume.  Apparently the specific gravity of the resin and catalyst are about the same. The scale would weigh up to a gallon but of course I wouldn't want to mix a batch that size.

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I have the calibrated pumps from Graham but often want to mix odd size batches of resin.  I picked up a small digital platform scale from Amazon for about $15. and have had no problems using a 2-1 weight ratio instead of volume.  Apparently the specific gravity of the resin and catalyst are about the same. The scale would weigh up to a gallon but of course I wouldn't want to mix a batch that size.

 

Bill:

 

The most common mix ratio I have found by weight is 1: 0.43 vs. a true 2:1, which would be 1: 0.5

 

So if you are mixing 2:1 by weight, you are "over cooking" it on the hardener side by about 5%. For anything in the range of 10 ml or less, you would have to have a scale that measured in the 10th's of grams to be that accurate. That would be about like trying to pick the fly crap out of the pepper. At that level, I'm simply going to use graduated medicine dose cups. I can make accurate batches as low as 7.5 ml with those.

 

On the other hand, over the course of a gallon of epoxy and 1/2 gallon of hardener, if mixing 2:1 by weight, at the end, you would come up about 6 oz or 3/4 cup short of hardener to finish your gallon of epoxy. To some, that might not matter......to others, it would.

 

Since this topic came up, I've mixed a quart or two of epoxy in numerous small batches and have found my graduated mixing cups or measuring by weight to be equally accurate. Measuring by weight offers a bit more flexibility with odd sized batches. Simply pour in some amount of Side A epoxy resin, multiply by 1.43 and that is the total weight of the finished batch. Pour enough Side B hardener in the cup to come up to that weight and you are ready to mix. BTW, some instructions call for measuring these into separate cups, then pouring them together. I always pour in to the same cup, figuring I'll leave less behind and over the long haul, get more complete and accurate mixes that way.

 

BTW, B&B pumps deliver 30 ml Side A and 15 ml Side B, for a "pumped" batch size of 45 ml per single stroke.

 

MAS pumps deliver 10 ml Side A and 5 ml Side B, for a pumped batch size of 15 ml per single stroke. I have no idea what various West pumps deliver, but I suspect it is closer to the MAS sized pumps.

 

All this means is that regardless of which pumps you use, you will likely want to find an alternative to using them for either large or small batches.

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Lastly, to help fair the tape, what are folks doing about peel ply? How are you using it and where are you getting it?

 

I don't claim to be an experienced builder but I have looked into the peel ply issue and found the following sources:

 

EconoPly:  http://www.peelply.com/index1.html

 

or https://store.airtechintl.com/htm/defaultnetscape.htm

 

EconoPly appears to be the cheaper and I believe B&B has said that it's the brand they use when they use peel ply and find it satisfactory.

 

 

If you go to the airtech site, they actually list four different choices for the peel ply.

 

Is one of those preferred? If left to my own devices, I'd probably order the 4th one.......the heavier silicon coated version.

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Back to working with the selved edges of tapes, I didn't get many takers on that one. I have used a number of methods.......everything from a spoke shave to block plane to cabinet scrapers and surform planes.......large and small.......and doing this while the epoxy is still a bit green and soft. But that still leaves a bit of a bump to fair out. So what I have come to prefer is to simply take a sharp utility knife or even razor blade and simply trim it off. Catch it as it is just starting to kick and it will trim easy and lift right off. That leaves a clean edge that won't take much fairing to deal with. You will only lose 1/4" or so from each edge. If that leaves you concerned you won't have enough tape left, use one size larger width of tape.

 

If you cut your own tape from a wide roll, you may have the wild, unraveled edges to deal with. Same trick can be used to clean those up (woven or biaxial). If you want a really clean edge, put down a strip of masking tape and let your glass tape overlap onto it a bit, then use the edge of your masking tape as your straight edge cut line, then lift off the masking tape.

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Howard.

 

I find that a couple of swipes with a paint scraper when he resin is green will take off the selvedge edge to a level that when you put on a couple coats of resin to fill the weave, leaves a perfectly adequate finish for the inside of the boat.

 

I don't mind being able to see the tape under the paint on the inside of the boat as long as it is even and smooth. I rarely sand the tape on the inside.

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