Repair with fiberglass?

On 15 Sep 2007 23:57:07 GMT, "Doug McLaren" wrote in :

Nice pix.

BTDT. Pix here:

I think I used medium CA on the exposed fiberglass first, thinking it would soak in better than epoxy. YMMV.

I probably also roughed up the gel coat to try to get a better bond for the epoxy/fiberglass band-aid.

Scratch that--I put the band-aid on with medium CA, too. I didn't want to mess around with epoxy, I guess.

The other places where the gel coat got broken off, I used CA & microballoons (first repair--my crash) and epoxy and microballoons (a friend's crash).

All of that stuff looks horrible both in the picture and in Real Life (tm), but it's under the wing and doesn't show in the air.

I've used epoxy and CA with fiberglass. Both seem to work well.

Some folks spray the cloth with ... uh ... 3M Super 77 contact cement. I haven't tried that.

If you use a sharp knife (#11, new blade), a straightedge that you can press down right where you're making the cut (a piece of aluminum works OK), cut on the bias (a 45-degree angle away from the way the weave, and use a soft cutting surface (I have one of those green self-healing pads), you can minimize the fraying.

Painting is optional. I believe in Ugly Insurance myself (as you can clearly see in the pix).

We broke it. We fixed it. It still flies. If anyone complains about how bad the plane looks, I'm willing to let them take it home and improve it all they want.

Marty

I have used silk and fiberglass resin to repair cowls. Sand and clean the area to be repaired, paint on a thin coat of the resin, lay down the silk where you want it, then paint on a thin coat of resin over that working it through the silk. Two layers of silk or any other light thin strong fabric will work. A light thin cloth will form to the curves easier.

Epoxy is to thick and dries too quickly to effectively do this and thinning epoxy with acetone is a pain in the ass. Fiberglass resin is already thin and easy to work with. It's available at Walmart for $10.97 for a quart. You mix 10 drops of hardner per ounce of resin, at least you do with the can I got. Work with 2 to 4 ounces at a time in a plastic mixing cup. I just use cheap 50 cent brushes and throw them away when I am done. You can use acetone to clean the brush out if you don't want to use a cheap brush.

You don't have to use epoxy with the fiberglass cloth. You can wrap a piece of saran wrap around your finger and push medium or thick CA into the cloth. Saves lots of time. Is usually lighter and is much, much quicker.

Ed Cregger

Really sharp scissors, and cut it on an angle, not along the warp or woof. Patches cut with the threads running at 45=B0 across them will conform to compound curves, too. Polyester resin (fiberglassing resin) will eat some plastics. If your airplane is made of foam or styrene or acrylic or ABS, don't use it. Epoxy is safer.

Dan

Fill in any gouges with some filler and smooth the surface. I like wall board compound. Let it dry real well before sanding. If needed, prestabalize the break with a drop of CA to make the structure rigid while you work on it. Your final surface will be no better then what you start with so get it smooth before you get out the epoxy.

Cut the glass cloth on the bias to reduce fraying to a minimum. It is better to use two or four layers of a light cloth vs one layer of heavier cloth to get smooth fits. Use a finishing epoxy for the best results. Stuff like ZPoxy is real easy to work with. West system products are too viscous for best results in model work. They will work but are a pain in the ....... Rough the whole surface you are bonding to then just wet it with epoxy and lay the cloth over the wet surface. Work just enough epoxy into the cloth to wet it out then lay the second layer over it. Work on the second layer with a plastic tool you can get at any auto parts store or an old credit card for putting on body putty to work excess epoxy into the second layer. Usually what you put down to wet the first layer is enough to wet a second layer also. Clean the card right after use with acetone or MEK or you will only use it once. Ethanol will also work but is slower and not as good.

Finally cover the whole area with peal ply. Peal ply is simply a polyester cloth. I have used scraps of polyester woven cloth from my wifes sewing bin in emergencies and it works fine. If you have a big bend in the part being patched it will work better then the heavier commercial peal ply. Let it cure 24 hours or more and peal off the peal ply and you will have a smooth surface. Much smoother then you can get with a regular layup. You need enough epoxy in the glass to wet the peal ply out fairly well. But beginners always have more then enough epoxy that this is not a problem. Make sure it is polyester if you are using scrap cloth. Easy to do by testing and seeing if it will peal off the cured surface cleanly. Any cotton in the cloth will be a disastor.

Will the patch be invisiable? Nope. But it will not have rough edges and splinters sticking out that will grab a hunk out of your hand like a fish hook. And there is no stronger patch you can make for the tiny weight you added unless you go to carbon cloth. This will work on any plastic or wood.

Fast, very strong, easy, neat. I have stuck a fuse busted clear in half back together this way and been flying in 48 hours.

wrote

Good recommendations. One thing though, is your recommendation of wallboard filler compound.

It is heavy, and lightweight spackling compound works as well, and is much lighter. Have you ever tried it before?

Whatever the stickum you use to cover screws and fill the seams between hunks of wall board is what I have used. If you are filling enough gouges that it will take more then five grams dry weight you have not done much of a job of lining up the original busted parts. If you have a hole slap a hunk of real thin balsa behind it and use the stickum to smooth it out. Make sure it is fully dry before you sand it to shape. Maybe the stickum is spackling compound? Beats me. Buy a gallon and it will be spoiled long before you use it all but a gallon only costs a few bucks.

wrote

Called joint compound.

True, but you know as well as me, that all weight counts against you. There is a lighter alternative, is my message.

Nope. You need to go to the hardware store and look in the area where they have nail filler putty and stuff. Lightweight spackle is used mainly for filling nail holes, and repairing small defects in walls. It is probably a quarter of the weight than the stuff you use, and acts almost the same, except that it is TONS easier to sand. The common size is probably around a pint or less, usually in a white plastic pop top container.

True.

Try some, sometime. It is great stuff. You can make it even tougher by getting it sanded into shape after it dries (and that is another big advantage; it dries in a tenth of the time) and then flooding it with CA thin glue. It is much more porous than regular joint compound, so it wicks up the CA great.

I use regular "heavy" spackling. I can't explain why, but I don't care for the light weight spackling. Joint compound is too difficult to sand when spackling is available.

I should say that I don't suffer a weight penalty with heavy spackling because I fill in all medium to large voids with scraps of balsa, then resand until the surface is very smooth. Then I use the heavy spackling, but, again, I sand it off so that only small white streaks of spackling are visible. Most of my filling is done with light weight balsa.

Ed Cregger

"Ed Cregger" wrote

That is another good way to go.

More than one way to skin a rabbit, a wise man told me!

Along those lines, I like micro ballons in Ambroid or Sigment. I also have some pre-mixed stuff that dried out long ago. You can put micro ballons in fiberglass resin but there's that sanding part........ mk

So you use light weight spackling to save weight, then add weight with CA to harden it up. Might as well use the regular stuff.

"Vance Howard" wrote

No, I usually do not. I just included that tip in case the repair was in a place that needed extra strength.

The heavy stuff would not be as tough without adding the CA, as the lightweight stuff with the CA, also.

Hey, it is just a suggestion, that I have found to be useful at times. I especially like using it on sheet balsa areas that are going to be covered with Monocote, or something like it. The finish of your Monocote is only as good as the surface underneath it. (but you knew that)

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Now that we're talking about fillers, I like to use phenolic micro balloons (brownish) for making fillets. I've used epoxy and polyester resin as a binder. I'll have to try Ambroid or Sigment. Never thought of trying that before.

It seems to me that there was one spackling product that negatively reacted when used with either polyester resin or epoxy resin, but I can't remember which one it was. Anyone?

Ed Cregger