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Old Apr 15, 2007, 03:36 PM
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Brownsburg, Indiana
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Question
How to fiberglass over sheet balsa?

I'm working on my second model that requires 'glass over balsa finishing. I thought I learned my lesson on the first project. I can never get enough extra epoxy off the 'glass or I end up with bubbles and wrinkles. I didn't thin the epoxy this time and maybe I should have. I'm using West Systems epoxy I have around from my many boat projects. Good stuff! But it seems like the more you thin the stuff the more air voids I get under the glass. I tried a plastic squeegy and a rag to get most the excess off. It's not too bad, but I want a nicer finish on the top of the wing. That's one thing I've learned over the years, start on the bottom of anything and the top will always look better. I looked in the archives and found that one guy used acetone to thin, but then I seem to get voids. I heard about using 3M super 77 spray adhesive to keep the glass down. Does that work? I'm using 3/4oz cloth by the way, light stuff.
Thanks, Jay
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Old Apr 15, 2007, 04:24 PM
the-plumber
Joined Feb 2003
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Quote:
Originally Posted by flying jeep
I'm working on my second model that requires 'glass over balsa finishing. I thought I learned my lesson on the first project.
I use West Systems thinned 50% with acetone. Never had a bubbling problem.

I also use up a couple full rolls of paper towels during the process.

Using the paper towels the way you would use a paint roller, blot up all the thinned epoxy the paper towels will hold.

Then peel the epoxy-laden layers off the paper towel roll, and do it again.

When no more epoxy comes off the 'glass, you're done with the first coat.

I always apply a second coat of thinned epoxy after the first coat fully cures, to help fill the weave. As with the first coat, blot the excess with a roll of paper towels.

Makes for lots of paper towels in the trash bag, and no excess epoxy on the model.

Fill and paint as you wish.

A whole 'nother way to glass balsa (or anything else, for that matter) is to make 'glass wing skins.

See the tech tip Fiberglass Skins
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Old Apr 15, 2007, 04:41 PM
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FredN's Avatar
Cary, North Carolina, United States
Joined Jun 2001
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I found this information useful: http://www.airfieldmodels.com/inform...nish/index.htm

I used cloth and ez-lam from: http://www.acp-composites.com/
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Old Apr 16, 2007, 09:39 PM
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Brownsburg, Indiana
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[QUOTE=the-plumber]I use West Systems thinned 50% with acetone. Never had a bubbling problem.

I also use up a couple full rolls of paper towels during the process.

WOW! Did that work great! I read your post and thought for a moment. Then I went out and ripped off the glass before it set up. Tonight I did as you suggested and I got brave enough to do the whole bottom side at once. It worked great! So far. It hasn't set up yet. But the paper towels worked great! I haven't told the wife where the kitchen roll went

Will this system work if you cover half a fuselage at a time? It sure turns 3/4 oz glass to almost wet tissue paper soft.
Thanks, Jay
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Old Apr 17, 2007, 09:04 AM
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Quote:
Originally Posted by flying jeep
I heard about using 3M super 77 spray adhesive to keep the glass down. Does that work? I'm using 3/4oz cloth by the way, light stuff.
Thanks, Jay
I like to use a bit of spray adhesive when using 0.5 - 0.75 ounce cloth. Rather than use 3M 77, which tends to be too thick, I prefer 3M Spray Mount Artist's Adhesive. Cheapest at Michael's Craft Stores than Artist Supply Stores.

This adhesive spray is a fine mist and remains tacky for some time. A little care is needed when spray adhesive is applied to light glass as the fabric can be blown away. To hold the fabric during spray application, I spray a very light mist on a large piece of cardboard and let dry for a half hour. Then lay the fabric on the cardboard and gently press the glass down at points along the fabric edges. Then a very light spray, from about 12" away, provides enough tack to hold the fabric to the balsa, or other substrate.

I find I do a faster and better job of applying epoxy when the fabric stays put.
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Old Apr 17, 2007, 09:46 AM
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Australia, VIC, Cranbourne East
Joined Apr 2004
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Doesn't anyone seal the balsa first?
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Old Apr 17, 2007, 12:00 PM
the-plumber
Joined Feb 2003
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Quote:
Originally Posted by flying jeep
I haven't told the wife where the kitchen roll went

Will this system work if you cover half a fuselage at a time? It sure turns 3/4 oz glass to almost wet tissue paper soft.
Works jes' fine on large items.
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Old Apr 17, 2007, 12:02 PM
the-plumber
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Quote:
Originally Posted by olmod
Doesn't anyone seal the balsa first?
I don't.

I prefer having the thinned epoxy penetrate the balsa sheeting - adds immensely to the strength and increases damage resistance quite a bit.

The thinned epoxy only penetrates about 1/16" or so, and the trade-off in weight versus increased strength/damage resistance is IMHO well worth it.
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Old Apr 17, 2007, 06:57 PM
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I covered the top of the wing tonight in one piece. What a nice job if I may say so myself! Once I had it all wetted out I trimmed around the edges (about a half inch extra) and rolled it under to the bottom side. I blotted/rolled off the excess with a roll of paper towels, and as the Brits say, Bob's your uncle! This stuff works so well once it's wetted out I can see doing half a fuse at a time. Will you see a little of the overlap seam?
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Old Apr 19, 2007, 12:36 PM
the-plumber
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Quote:
Originally Posted by flying jeep
Will you see a little of the overlap seam?
You'll see the outermost edge. A bit of filler and feather sanding will hide that.
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Old Apr 19, 2007, 09:16 PM
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Hey Plumb,
This Dauntless (Rittingers plan) I'm working on is a one piece model. I covered the wing prior to gluing in place. Just to make it easier. Should I cover the tail before gluing in place? With Monokote, any seams in these areas would be next to invisible. But this is my first "glassed and painted" model and I'm "learning" the hard way. It's too bad I can't tack the stabilizer on while I attach the tailcone and verticle fin fillet blocks, and then remove the stab to sand everything down to shape.
Jay
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Old Apr 20, 2007, 02:02 AM
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London, UK
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I also plan to use Spray Adhesive to mount the cloth prior to epoxy application...(3M Paragon glider fuselage and centre wing section)

related Question 1: will the Spray Adhesive form a barrier that will prevent the epoxy from penetrating the balsa and hence limit the strength benefit?

Question 2: given that the tail and stab need a wood-wood bond what is a neat and simple way to make sure these areas are fibreglass free? Masking tape?

Question 3: If fibreglassing the nose of a fuselage how do you deal with compound curves?...
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Old Apr 20, 2007, 06:17 AM
Building a Corsair
rwright142's Avatar
Indianapolis, IN
Joined Jan 2006
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flying jeep,
Any pictures? I am building a 1/6 scale F4U Corsair and will be glassing it too - I've never glassed, and am learning a lot for you all.
BTW, I'm not far from you - I'm in Mooresville.
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Old Apr 20, 2007, 08:49 AM
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New Jersey, USA
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Quote:
Originally Posted by arukum17
I also plan to use Spray Adhesive to mount the cloth prior to epoxy application...(3M Paragon glider fuselage and centre wing section)

related Question 1: will the Spray Adhesive form a barrier that will prevent the epoxy from penetrating the balsa and hence limit the strength benefit?
I normally thin my first coat of coating epoxy with about 10% acatone. I've never found a light application of 3M Spray Mount to form a barrier. Acatone is a solvent for most spray adhesives. Even using alcohol for thinning works. For some of my projects I'll cover a balsa part with fabric sprayed with Spray Mount and bond it to the wood with thin CA, sand and then coat with epoxy.


Quote:
Originally Posted by arukum17
Question 2: given that the tail and stab need a wood-wood bond what is a neat and simple way to make sure these areas are fibreglass free? Masking tape?
I wouldn't worry about a good bond between fiberglassed parts using epoxy so long as the bonding area is sanded. Film covered wood or paint covered wood can be a problem.

Quote:
Originally Posted by arukum17
Question 3: If fibreglassing the nose of a fuselage how do you deal with compound curves?...
This is where the spray adhesive works best. The weave of the fabric can be worked into concave and convex shapes. There are limits to the conforming abilities of the fabric, so when folds develope the fabric needs to be cut and perhaps covered in seperate pieces.

Spray adhesives should be used to provide TAC, not bonding. Balsa parts need to be dust free before laying the glass down.
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Old Apr 20, 2007, 10:44 AM
the-plumber
Joined Feb 2003
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Quote:
Originally Posted by flying jeep
It's too bad I can't tack the stabilizer on while I attach the tailcone and verticle fin fillet blocks, and then remove the stab to sand everything down to shape.
Jay
If all you want to do is get the stab in place so you can position and glue the other bits, you can tack it on with a -small- dab of hot glue or craft glue (Ailene's Tacky Glue works for me).

Both hot glue and "tacky" glue can be pulled back apart without damaging the structure if you mind the -small dab- rule.

Then you can finish the stab before mounting it permanently.
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