Z Poxy Cowl Repair
 

I want to find out if anyone else has this problem, as I can’t find it discussed anywhere else. I hope this is the right place to post this question.

I am rebuilding and recovering a Velox II Revolution ARF and will switch from a Saito 110 to a DLE 20.
I wanted to repair the cowl and cover the holes I had cut out for the cylinder head and muffler on the Saito that had been installed on the plane.
The cowl had two large holes 2 to three inches around plus ¼ inch holes for fuel lines and needle valve.
I planned on patching all the holes and repainting the cowl.
I have never done extensive fiberglass work before, only minor repairs. I don’t need a quart of resin, so I saw that Z poxy offered a 12oz finishing resin. I love their epoxy so I bought some.
Not to get too detailed, but I put styrofoam in the first cut out and sanded it to shape, matching the cowl pretty good. I used a light fiberglass to make it easier to shape and applied it with the Z-Poxy. When I finished it looked beautiful, I just had to wait until it hardened.
After the recommended 6 hours I was able to sand the rough spots. Then I noticed the patched area was weak and flexed easily when I touched it. Next day I mixed more Zpoxy and applied heavier fiberglass inside the cowl to strengthen the patch. While I was at it I put small patches on the ¼ inch holes.

Now the fun begins. It sat for 12 hours and the resin was still tacky to the touch. Later I put it in a 170º oven for 3 or 4 hours. Finally it seemed to be cured. But the patches on the holes were like paper. I checked my addition to the large hole and saw the new fiber glass was pulling up. I was able to pull the patch off like tape. It was dry but not hard, and didn’t stick at all to the fiberglass patch under it.
Upon checking the remaining resin in the mixing bowl, it is still soft and sticky after a full 24 hours.

I have gone back today with regular 30 min epoxy to strengthen the original patch. If that works I may have to sand down my previous repairs and just use epoxy.

My question is; is anyone else having problems with this product?
Before you ask, I don’t weigh it out or measure, but I watch how much I use from each bottle the same as I always do with epoxy,. This morning I saw the level in both bottles is exactly the same, so I am as close as can be to using 50/50.

Why would the first batch work and the second not? And is the ZPoxy resin to be used for large patches like this, or just minor touchups?

Thanks.
I guess this may be a long post for some people, but I was in the mood to write, and if you read this far maybe you can help.

I have never used that epoxy personally but I hear it is a good product. I use laminating epoxies (various brands) practically every day to make molds or cast moldings, or laminate surfaces. What you describe is unusual. Sounds like either the ratio A:B was off by alot, or alcohol or other solvent found its way into the batch. When laminating the inside I assume it was well cleaned of all oil residue and then sanded with 80 grit or a dremmel and drum sander. If the surfaces were washed with alcohol or other, you needed to make certain surfaces were dried thoroughly

Let me suggest that IF you decide to start over, use 1/32" balsa in the holes. Then use thin glass on both sides (about 3/4 oz or 1 oz).

Right now I'm thinking about sanding it all off and starting all over. I'll mix up another bath of zpoxy just to test.

Yes, the first batch stuck good on the fiberglass cowl. It was just too thin and very flexible. The second patch didn't even stick to the prior epoxy patch. I'm thinking about just sanding out what I've done and hope I don't take off too much more of the cowl and start all over with "regular" fiberglass kit.

Roy,

In my experience, Z-Poxy is a great resin to be used as a finishing resin. In other words, if you are fiberglassing a fuselage &/or wing it is hard to beat, because it wets-out and sands extremely well, has a reasonably long working time, etc. However, it is not a very good resin (in my opinion and experience) for fabricating; or, therefore repairing fabricated fiberglass parts. I have found it tends to be simultaneously both a little too flexible, yet brittle, when I have attempted to use it to fabricate cowls.

My recommendation echoes that of your last post, to essentially start over with a "regular" resin more purpose-engineered/formulated for fabricating parts.

Yes I bought some fiberglass resin at Lowes yesterday so will give it a try as soon as I "RePrep" my cowl. As I said I have never used the ZPoxy resin before and didn't do enough research before jumping in.

MTK: I am thinking about trying the balsa as a pre-fill in the holes. That sounds like it will make it easier. A thin layer of glass on each side will be strong enough? The cut outs are about 2inches by 3in.

Thanks for the help

Roy,
A 2x3" hole is medium sized. The fix I suggested will work well. Let me expand on the technique. After cleaning the hole and sanding as appropriate, use the hole itself as the template to cut the wood panel. I fit the panel and then ca it in place, before applying the glass. You want a good fit between the wood and the cowl with minimal areas to fill.

It builds into a nice and light yet strong enough patch. If you're nervous about its strength, you can always add a strip of glass around the perimeter then come back with a larger piece to cover everything and overlap the added strip. Thinner glass will feather easier into the existing cowl making a professional repair.

I think I'll give that a try. It may be a week or so before I can get started, but I'll try to remember to post my results

Thanks.

Again, I've been building model airplanes most of my life, started RC in the late 70s, but haven't done much with fiberglass. Nice to learn something new.

A word of caution. Lowes generally sells polyester resin for fiberglassing although I suppose they may have epoxy resin and I just haven't noticed. If what you bought was polyester resin and not epoxy resin, it may or may not work well for you. If your existing cowl is epoxy-based, the polyester resin will not adhere well to it. Epoxy resin, however, will adhere well to either an epoxy cowl or a polyester cowl and would therefore be a better choice if you're not sure what the existing cowl was laid up with.

+ 1 on post # 8

The mixing of epoxy is vary important, and the measuring with some resin's is critical, liquid Oz or by weight. That said I have found for laminating resin's they need to be WELL mixed to get consistent cure. Take Z-poxy is 50/50 by liquid so lets say you want 2 total Oz after mixing, best way I have found is to use graduated medical plastic cups and vary carefully add the parts just to the graduated line's and then stir with out wiping for at least 1minut per Oz, Note this is just my way.

Good Luck

Cheers Bob T
AMA13377