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Foamy epoxy

Lemmingman

Well Known Member
I am getting a lot better at this, but I am finding that I am getting foam in my epoxy when Im wetting the cloth. During the mix there might be one or two bubbles, I am very careful to mix easily. I drizzle the epoxy onto the glass and start spreading with my squeegie and before long LOTS of tiny bubbles have formed in the epoxy. The epoxy ridge is nearly white as a lightly draws it across the glass tape. Am I working it too much, should I put more on and squeegie fewer times, but take off more epoxy with each pass?


I found out about fiberglass tape, so I got a 50 yd roll and went to work this AM. First try was complete rubish, had to trash it. But the second attempt went very well, but I think I may have squeegied to much epoxy out. After applying the layup it seemed to absorb air...bubbles appeared where there had been none before. Is this possible? I was dilligent to look for the "whiteish" appearance that cloth that is to dry can exhibit and I didnt think it was.
 
I am getting a lot better at this, but I am finding that I am getting foam in my epoxy when Im wetting the cloth. During the mix there might be one or two bubbles, I am very careful to mix easily. I drizzle the epoxy onto the glass and start spreading with my squeegie and before long LOTS of tiny bubbles have formed in the epoxy. The epoxy ridge is nearly white as a lightly draws it across the glass tape. Am I working it too much, should I put more on and squeegie fewer times, but take off more epoxy with each pass?


I found out about fiberglass tape, so I got a 50 yd roll and went to work this AM. First try was complete rubish, had to trash it. But the second attempt went very well, but I think I may have squeegied to much epoxy out. After applying the layup it seemed to absorb air...bubbles appeared where there had been none before. Is this possible? I was dilligent to look for the "whiteish" appearance that cloth that is to dry can exhibit and I didnt think it was.

This does not sound right at all. I can whip the epoxy all I want, then pour a little on a cloth and lightly spread it (I use sections cut from a milk carton), then let it sit to wet the cloth, then apply it. I do a wet layer, then dry (roll it), then another wet. Never had this foaming. I have only used a 4-5 different formulations, but nothing like this. You might contact the supplier tech line and be ready with your cloth source information.

What brand/product and are you "thinning" with anything?
 
Not doing anything but pumping it from the cans (Wests) and stiring. Not thinning with anything. 2-pumps per batch and thats all.
 
Fiberglass tape has limited usefulness as it is hard to form it on complex surfaces. I just got a few yards of this stuff for everything: http://www.aircraftspruce.com/catalog/cmpages/7781.php

On spreading the epoxy, the "never fails" approach is to lay out the bids of glass (2-4) on top of a piece of clear plastic. Pour on the epoxy while moving around the glass. Do not spread the epoxy with a squeegee. Instead, cover the plastic/glass/epoxy with another piece of clear plastic. Now use your squeegee on top of this sandwich to spread the epoxy around and (equally important) to squeegee out any excess epoxy. When done, use your fiberglass cutting wheel http://www.aircraftspruce.com/catalog/cmpages/rotarypizzacutter.php
to trim off the edges of your sandwich so you have a perfect layup. Not cut the sandwich to the sized you want and only when ready to apply do you remove one of the clear plastic layers. Lightly wet the area for the layup with epoxy. Get the layup in place and remove the second plastic layer. Work the glass to shape. Cover with peel-ply and lightly work a squeegee on top of the peel-ply. Leave the peel-ply on until set. Remove the peel-ply and you are ready for more glass or a coat of mico for finish sand.

The best way to practice this is to make a 12"x6"x3" or so open wood box and try to line it with a fiberglass lay up. Cover the inside with clear packing tape so you can get the layup out after it sets. After the first try, do it again but this time fill in the 90 degree joints a little to round the intersection (and note how much better this works).

Carl
 
Thanks for the idea Carl. I haven't tried it with the top layer of plastic. I've been wetting each layer and then moving it to its final location.
 
It's just air working out of the cloth. Epoxy always turns milky white with tiny air bubbles when you squeegee it off cloth.

A squeegee is a slow and messy way to wet out a single ply of tape. You have a box of cheap chip brushes, yes?

http://www.harborfreight.com/36-Piece-1-in-Industrial-Grade-Chip-Brushes-61491.html

BTW, when you pull the wrapper off one of these, pick up the shop scissors and trim the raggedy tip, perhaps the first 1/2" or so. It will both spread and stipple better.
 
...I just got a few yards of this stuff for everything: http://www.aircraftspruce.com/catalog/cmpages/7781.php...

My condolences. The last time someone tried to give me a hundred yard roll of 7781 I sent them home with it to save myself the trouble of throwing it away. It is hateful undrapey stuff with a tight weave that doesn't wet out unless you just about pound the resin in with a hammer. It's great for resin infusion and resin injection like for circuit boards and Garolite. Wet layups, not so much.

Much, much better, especially to composites newcomers, is 7725. It is a 4-harness weave that drapes over anything and wets out easily and consistently with any reasonable laminating resin. Cut it on the bias (+/-45 degrees to the fibers) and it will go around almost any curve. It is our go-to glass for the non-carbon parts of our kit sailplanes.

7725 is sometimes called "Rutan BID" because of Burt's role in promoting it for moldless foam core construction. It is basically the same stuff as the Interglas 92125 that European sailplane manufacturers are so fond of.

Thanks, Bob K.
 
...BTW, when you pull the wrapper off one of these, pick up the shop scissors and trim the raggedy tip, perhaps the first 1/2" or so. It will both spread and stipple better.

They haircut easier if you do it while the plastic wrapper is still on. We use our open throat shear for this; one snip and done.

--Bob K.
 
A squeegee is a slow and messy way to wet out a single ply of tape. You have a box of cheap chip brushes, yes?

http://www.harborfreight.com/36-Piece-1-in-Industrial-Grade-Chip-Brushes-61491.html

BTW, when you pull the wrapper off one of these, pick up the shop scissors and trim the raggedy tip, perhaps the first 1/2" or so. It will both spread and stipple better.

Thanks for all the hints. The brushes are better at chasing the bubbles out of this. I also decided to let the working time of the resin work for me. After laying out my laminations and wetting them then covering with saran wrap (no 4mil around) I chased bubbles for a few minutes. Then I went inside, ignored some emails, checked what time my sons practice is tonight, checked some scores, looked to see when DST ends in Europe and went back to the emails I had ignored and re-read them only to ignore them again. By the time I went back out side, there were lots of new bubbles that were obviously formed from all the smaller bubbles. You are right about the squeegie, Dan. It creates that foamyness much more so than the brush.

Thanks for all the hints guys. This is definately an art, but I am starting to like it.
 
I would not use a piece of milk carton to spread epoxy. Milk cartons are made liquid tight by a coating of wax. use an old credit card, or what I often use is a playing card - I buy decks of cards at the dollar store. Or a hotel door key card.

+1 on the BID being better than tape. The only problem with cutting it at 45 deg is that the piece of cloth can be easily distorted so you have to be careful with it. But the 45 deg cut cloth is a joy to mold around curves.
 
My condolences. The last time someone tried to give me a hundred yard roll of 7781 I sent them home with it to save myself the trouble of throwing it away. It is hateful undrapey stuff with a tight weave that doesn't wet out unless you just about pound the resin in with a hammer.

Bob, I respectfully disagree, in part. I think 7781 conforms to compound shapes rather well. Posted an example just the other day, wrapping an entire oil cooler inlet duct with 4 plies of 7781, all in one piece:

http://www.vansairforce.com/community/showpost.php?p=1120096&postcount=12

I do agree about brush-wetting 7781 (a PITA), and yep, the tight weave is bad about trapping air. However, the tight, flat weave is also its best point; higher strength for the same weight, and less void space, so higher fabric/resin ratio. It also requires less filler when surface finish is important.

7725 is sometimes called "Rutan BID" because of Burt's role in promoting it for moldless foam core construction.

An aside; "BID" always struck me as an odd label for a non-symmetrical fabric. I think most of us dummies would assume a bidirectional fabric would use the same fibers and a similar yarn count for both warp and weft. However, 7725 is a 54 x 18 yarn count, with the weft (fill) being a "fat" yarn with three times the strength per yarn (5.7 vs 17 lbs). The heavy gauge fill yarn is why 7725, for the same weight, is thicker and more coarse, yet less strong. Note that (1) both fabrics are bidirectional, and (2) neither has equal strength in both warp and fill.

Hey, I'm not sayin' there is anything wrong with 7725, or that 7781 is absolutely marvelous. They're just different, and each has its own merits and drawbacks.

 
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