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alpinelakespilot2000

Well Known Member
I'm building a fiberglass rear skirt for my slider. Using tape as a mold between the canopy and the aft skin, I'm left with a small dip in the fiberglass layup where the tape sagged. At some places in the valley, the fiberglass is maybe 1/16-3/32" below the top surface of the fiberglass sitting on the canopy and aft skin.

I have both microballoons and flox. I understand flox has some strength qualities that microballoons does not, but does filling the sag described above with flox as opposed to microballoons serve any useful purpose here? Is flox even used for this kind of thing? Would it, for example, provide a tougher top exterior surface for my canopy skirt than microballons? Would it adhere to the cured, and peel-plyed, fiberglass any better? Does it sand or finish out any better or worse?

Any thoughts for this fiberglass novice much appreciated.
 
Flox is far harder to sand, and you may damage surrounding areas if you're not careful. Pure microballoons are a little soft, but probably fine... I know some guys who use a mixture of both for nonstructural applications where they want a little extra durability.
 
alpinelakespilot2000 said:
I'm building a fiberglass rear skirt for my slider. Using tape as a mold between the canopy and the aft skin, I'm left with a small dip in the fiberglass layup where the tape sagged. At some places in the valley, the fiberglass is maybe 1/16-3/32" below the top surface of the fiberglass sitting on the canopy and aft skin.

I have both microballoons and flox. I understand flox has some strength qualities that microballoons does not, but does filling the sag described above with flox as opposed to microballoons serve any useful purpose here? Is flox even used for this kind of thing? Would it, for example, provide a tougher top exterior surface for my canopy skirt than microballons? Would it adhere to the cured, and peel-plyed, fiberglass any better? Does it sand or finish out any better or worse?

Any thoughts for this fiberglass novice much appreciated.
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Flox is next to impossible to sand. Dry micro is easy. Flox is only used for structural uses.
You now know why tape is a poor mold material. You would have been better off using a thin sheet of balsa covered with clear packing tape for release.

I would just fill it with dry micro and forget it.
 
I use a lot of POLY-FIBER SUPERFIL part number 09-28250 from ACS . It is easy to sand and will adhear very well .
 
WEST Systems

I would vote for WEST Epoxy and their 410 filler...

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This combination is works well, is easy to apply and easy to sand. I would only mix enough microballons in to make the mixture non-runny...

gil in Tucson
 
gpiney said:
You now know why tape is a poor mold material. You would have been better off using a thin sheet of balsa covered with clear packing tape for release.
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Probably a good idea, Greg. I'm just following the experience of a couple other builders who ended up with nice skirts layed up over tape. The nice thing about fiberglass, though, is that it's pretty cheap so if this first one doesn't work I'll build another one and check around to try to find a source for thin balsawood. Maybe then I wouldn't neet to use much of any filler. Not sure I'll be able to find it locally though.

If the microballoons don't go well, I'll give Superfill or the 410 a try. I'm just trying to cut down on the number of cans of filler I have laying around.

Thanks for the replies.
 
gpiney said:
Flox is next to impossible to sand. Dry micro is easy. Flox is only used for structural uses.
You now know why tape is a poor mold material. You would have been better off using a thin sheet of balsa covered with clear packing tape for release.

I would just fill it with dry micro and forget it.
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I did a lay-up of e-glass on a waxed piece of plastic laminate (countertop material), cut out to make a skirt, then used that as the base for further layups.

See:

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118_1878_1.jpg
 
Vernon-
Nice skirt! Any hints on how you layed up the "dog house"? I've found that fiberglass doesn't like inside corners very well but your's appear to be relatively square compared to other fiberglass skirts I've seen. Again, looks nice. Thanks for the pics.
 
alpinelakespilot2000 said:
Vernon-
Nice skirt! Any hints on how you layed up the "dog house"? I've found that fiberglass doesn't like inside corners very well but your's appear to be relatively square compared to other fiberglass skirts I've seen. Again, looks nice. Thanks for the pics.
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My recollection of the doghouse is hazy, but as I recall, it's got a lot of micro on top of the initial cloth layups. The initial layups for strength, and the micro for shape. This photo helps. Lots of sanding, of course!

Vern

118_1803_1.jpg


More photos http://www3.telus.net/aviation/flying/RV-9A/photos/Fuselage/Canopy_photos.html
 
Flox is used to thicken up resin when making a layup if the straight resin is too thin and will not stay where you want it. Can also be used to get a good corner - if the mold has a sharp corner then put resin/flox in the corner and lay up over it. As noted above it is hard to sand and heavy.

Micro is used to create a filler from resin and has all the structural properties of filler (ie none), but it is easy to sand.

If you're worried about durability another couple of layers of glass might be the answer.

Pete
 
Good answers

There have been many good answers. For the small gap you have either micro and epoxy will work great. With a gap that small you can also use Rage auto body filler. This stuff bonds extremely well and sands like butter. It is a catalyzed filler so it doesn't shrink.

I also have some 3/4 oz glass cloth I use for my RC stuff. This is extremely light but strong cloth. On one area of my Targa strip for my Tip up I filled a couple of areas. After completing, I layed a small piece of this cloth over the work to tie it all together. Everything was feathered in with auto body filler to perfection.

Don't be afraid to experiment with glass either. I made mold from my neighbors rudder cable fairings and layed up my own with fiberglass. Lots of versatility.
 
Balsa...

Steve,

Just in case you need balsa wood for this part of the project, or later, the aviation department @ Home Depot sells it. You have to look for it though....it is over by the interior crown molding and trim, in little bins that lay the balsa in a horizontal manner. All you will see are the little narrow ends.

C-ya,
 
Micro is for bulk. Flox is for toughness. Cabosil (fumed silica) is for thickening, or to be more precise, to make it thixotropic so it doesn't run. For filling you can intermix any proportion of the three to get the properties you want. Micro or flox does thicken epoxy, but it will run down the part until the epoxy gels. When mixed with a slow-set epoxy it will wind up on the floor.

Don't buy fancy nylon peel ply unless you plan on using an oven for cure. Plain old polyester aircraft fabric works fine. The guy in your EAA chapter who recovered a Taylorcraft last year has plenty of scrap peel ply in a box under his bench <g>

Sand well to prep for filler if you didn't use peel ply. Paint on a little mixed epoxy, let it sit a moment, then wipe off the excess and apply the filler. This prevents the sanded surface from soaking up epoxy from the filler at the interface; you get a better bond.

You can lay glass cloth is around tighter corners (inside or outside) if you cut and lay the fabric on the bias.

Polyester body filler over epoxy may make you unhappy a few years down the road when it peels and cracks. Micro and epoxy applied as above is trouble-free. Only drawback is a longer time to cure.

When filling a surface with micro, apply enough to sure you can sand and get the contour you want with that one application. If you apply another coat later to fill a low spot you missed, it won't sand exactly like the first application unless you were very careful to mix the exact same proportions of epoxy and micro. The result can be a wavy surface because some spots are softer or harder than others.
 
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