Using Bondo
 

I am wrapping up my build.

I used epoxy and micro balloons to fill the window cracks and on top of the cracks I used epoxy and fiberglass cloth. I used a lot of epoxy and fiberglass on the forward lower windshield.

After a lot of sanding, I am using a light coating of bondo to smooth out the edges and fill the little pin holes. I have already done it, so don't warn me not to do it..:)

Now my question: I want to fill the crack and pop rivet holes on the edge between the fiberglass canopy and the aluminum fuselage. It is pretty easy to do it in bondo, and it is not anything structural. Before I do this, I thought I would ask for your opinions. Note, if I fill it with epoxy and micro balloons, I will probably still finish coat it with bondo.

Just out of curiosity, what kind of Bondo are you using?

You might fare better using some of the lighter/more flexible glazing putty offerings from companies such as Evercoat.

You might want to consider something not only a lot more flexible but with much greater elongation if you're sealing across different materials. Aluminum and fiberglass have considerably different rates of thermal expansion and using a brittle material might not be the best choice.

Dave

I used a little Bondo on my horizontal stab when I built my -4 in '88. Has not cracked in 28 years.

Bondo, Evercoat
 

Ever coat makes a couple of different versions. One is Rage. Good stuff. This is for thicker requirements. Then they make a version for finish filling called 416. It is light and sands like balsa wood but is hard.

The key is to insure you use a type that is catalyzed because it will set. I made the mistake of using some Stanton on my first plane. This is an un catalyzed automotive filler. Works good and sands nice but shrinks and never full cures. After learning that, I removed it all!! That was a pain.

Some people will recommend you don't use fillers like this. They work good, are easy to sand and cure hard. Good luck.

Here is what I did...
 

I called my friend who has completed his RV-10. He told me he put a thin layer of fiberglass over the canopy to fuselage gap. He said there is a good chance that a crack will form without the fiberglass topping. So I first filled the gap (small gap) with epoxy and micro balloons, then applied a 9 oz fiberglass cloth.

Now I am going to sand the rough edges and again use bondo (bondo gold for professionals :D) to smooth out the edges.

So thanks for all the recommendations, as I struggle along...

I know several aviation painters that use the Evercoat product. It is pretty inexpensive and available from your local auto paint distributor.

Check the TDS on this product, it is for application direct to metal, (al and Fe) for automotive. One of the few allowed for direct to metal to meet todays corrosion resistance.

One famous RV painter recommended it ( when I asked )to be applied with a thin steel squeegee for the pinholes.

West Systems Marine has several filler additives for their epoxy system, which I used to create the cowl to windshield fairing (fiberglas) and the targa strip (carbonfiber). I've used the heck out of 407 light fairing powder. Its purpose is to fill small voids like pin holes. That and microballoons has worked good for me. I suspect that Bondo is just epoxy with a sh*t load of 407 type powder in it. At least it sure looks and works like Bondo when I mix it that way.
YMMV.

Keep in mind BONDO ( company) was purchased by 3M years ago, Bondo has always made 3Ms fairing compounds and fillers..

so quality is there..

also I am in the Marine Industry and work with composites and most of the manufactures mentioned on here like West, evercoat etc..

I look forward to starting my build and getting all this priceless knowledge