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polyester vs. epoxy for covering / filling

Old 10-06-2015, 08:48 PM
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Default polyester vs. epoxy for covering / filling

Having started building balsa planes way back, I have always used polyester resin for glassing, and mixed with phenolic or white micro balloons for easy sanding putty. After all, that's what Dave Platt did/does and doing things his way has always worked. Now days, I'm thinking epoxy resin may be the way to go : It doesn't stink up the house, seems to have a longer shelf life, and it works w/ the relatively resent peel ply method. I'm assuming polyester resin would permanently glue the peel ply down since it's polyester also. One thing I need to know is what kind of light weight filler to mix with epoxy resin for fillets, filling low spots on the balsa, etc.Does epoxy and microballoons sand as well as the polyester mix ? Does anyone use and recommend West Systems 410 filler with their epoxy ? Is it light and easy to sand/feather ? Any opinions are welcome. Thx. 'buff
Old 10-07-2015, 04:08 AM
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Yes,, the 410/epoxy sands very easy, the thicker you mix it up the easier it sands..
I went to epoxy for the smell too, but also once the poly mix didn't go off right and it ruined a job, Nothing beats the reliability of epoxy IMO

I bought a gallon/quart of West system epoxy/hardner almost 20 years ago, I'm down to about 1/4 gallon and it's still works great.

good luck

p.s.
last week I used some 410/epoxy to reinforce a gap that was allowing firewall flexing, I mixed it up wet so it would flow



If you scan this thread,, I used the combo several times repairing that bird, as well as the original build,
http://www.rcuniverse.com/forum/seap...-15-years.html
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Last edited by scale only 4 me; 10-07-2015 at 04:14 AM.
Old 10-07-2015, 08:20 AM
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Now, that's the kinda info I was looking for. I enjoyed and learned plenty from your Kingfisher re-re-re-re-rebuild to boot ! Was Orville and Wilber there for the maiden ? Your remark about the gallon of West epoxy was a jaw-dropper. I remember ordering 4-5 qts. of Hobby Poxy polyester finishing resin on sale and put 'em on the shelf where they hardened into taffy in a year or two. Looks like I'll be switching over to the epoxy / 410 filler route. Thanks much for the info. Very encouraging . 'buff
Old 10-07-2015, 09:28 AM
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Epoxy for me too. I have been using the Z-poxy finish resin now, thinned 50% with acetone so it flashes off faster and leaves no moisture trapped under the finish. I use a small trim paint roller to apply it, so I get just enough to wet the glass and not have excess. A lite sanding with 150 grit and then I roll on automotive primer filler unthinned. It fills in the weave very well and I then sand off almost completely. any low spots are filled with automotive spot putty, then a light primer coat to top off. I used poly resin once and the smell was horrible and it was old and never kicked completely so it was a real mess.
Old 10-08-2015, 07:47 AM
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Well, thanks on that too, Raptureboy. I've always used the polyester resin straight out of the can with a 1 in. or so paint brush, but I noticed on all the you tube and forums that guys pooled it up and then spread the epoxy type with a spreader. This suggested to me that the epoxy resin was thicker than the polyester type, and maybe needed to be thinned for our type model glassing. Now I know it is ok to thin it with acetone ( some of the recommendations were for denatured alcohol). Based on your guys recommendations, I'm going to switch over and do some practice swabs with different thinners and try the roller as well. Thanks much ! 'buff
Old 10-08-2015, 01:46 PM
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I've always used alcohol too, First I've ever heard of using acetone,
Thinning really depends on what you're doing, for laying 1/2 or 5/8 oz cloth, yes thin the first coat so it soaks in well and brushes easier, the second coat can go on a little thicker since you can brush it out more (cloth won't move, etc.)

good luck
Old 10-09-2015, 03:52 PM
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Wow I have not use polyester resin even though it was widely recommend years ago , I'm not fond of the smell of epoxy but it dose no last to long and yes you can mix micro ballons with it.
does anyone vacuum bag anymore ?

jayd
Old 11-28-2015, 05:01 AM
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Originally Posted by jayd3
Wow I have not use polyester resin even though it was widely recommend years ago , I'm not fond of the smell of epoxy but it dose no last to long and yes you can mix micro ballons with it.
does anyone vacuum bag anymore ?

jayd
I bag all of the sheeted surfaces in light vacuum (about 3 psi negative). That's the adhere the skins onto the foam. I've also played with bagging the top covering on the surfaces using finishing epoxy. West Systems has a good laminating epoxy that you can use for finishing. US Composites does also and it is much less expensive, but cures a little slower (48 hours instead of 24). There are several sources of pretty good finishing and laminating epoxy systems on line. I don't use the hobby epoxies; not thin enough

But for finishing surfaces it is hard to beat Klass Kote epoxy paint. I apply coverings (light glass, carbon tissue, etc) with clear epoxy paint. It goes on far thinner and hence lighter than finishing epoxy. It needs a good filler coat to fill weave. Full cure takes a week or more but the surfaces are ready to handle in a couple hours and sand in 12 hours or so at 70 degrees
Old 11-28-2015, 08:18 AM
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West Systems has a whole line of products and are all very good. I use just glass my latest project a p-51 I put together from plans. I used the peel ply method to save time over the old sand, sand then sand some more method. Peel ply makes working with glass a real joy. Like for example, glassing your wings center section joint. That is one task I used to hate because it was such a messy and sanding, sanding , affair. Not so if ya us peel ply. I put on two layers of 6 oz cloth 5 inches wide, over the wing joint then apply peel ply smooth it out blend it into the non-glass edge and when setup, remove the peel ply and it is DONE with almost no sanding. It has a super nice fabric like finish ready for primer only light touch up. Give it a try you'll never go back to old way even with the added cost.
Old 12-04-2015, 03:04 PM
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Based on Harry Higgley's advice I have always heated epoxy to make it thinner, there are two cautions when heating epoxy: 1 is the epoxy will cure faster the hotter the thinner and faster so this is not recommended for 5 min quick set, and 2.and while I have not tried heating after mixing my perhaps wrong understanding is that it is less effective in thinning and makes for very fast setting.
I heated some of the thick old 5 min stuff I had and it got very hot while setting and set in about 2 min or less. To much heating during setting could be detrimental?
I'm going to try adding some acetone to some 20 year old 5 min set I have that the resin has gotten pretty thick, if I add acetone to the bottle will it shorten it's shelf life ?
I've had paint thinned with acetone set up in the can?


Jay
Old 12-06-2015, 04:44 AM
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This is great information.

https://www.youtube.com/watch?v=ujk-wBQDUSk

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