Another Pinhole Question

[mlwynn]

I am working on my first major fiberglass project: the wheel pants. Per the suggestions on the list, I prepped the part till I thought it was perfect. Then I sprayed a couple coats of primer. It became clear that it was far from perfect so I have been resanding, filling etc and now do have it pretty close to perfect. There are still a lot of pinholes to fill. I am planning to use Dan Horton's suggestion of West systems clear coat thin epoxy. I was trying to figure out if I should remove the primer before I squeegee on the clear coat. I have been using Stewart Systems primer. It is water based and very non-toxic. It can also be pretty quickly removed with MEK.

So, squeegee on the clear coat without any further prep? Sand off the primer? Remove it with MEK and then apply the clear coat?

Thanks,

Michael Wynn
RV 8 Fiberglass
San Ramon, CA

[flickroll]

I have the exact same question. The only difference is the primer I'm using is is PPG K36

[David-aviator]

I just finished the lower cowl and it had a million pin holes.

My method is old fashioned and goes back to the early canard days but it works. Go find some spotting putty by 3M. It comes in a tube like tooth paste. I think I found it at Auto Zone. It is colored red.

Take a plastic squeegy about an inch wide and apply this stuff very thin, just enough to fill the hole. Let it dry about 20 minutes and go over it with 320 paper. If it is put on right, after the sanding you won't see any red remaining except a tiny speck where the hole was.

It works for me.

[flickroll]

Originally Posted by David-aviator

Go find some spotting putty by 3M.

David - will that stuff stick long term when applied to either raw fiberglass that uses epoxy resins, and/or to one of the primers that were mentioned in this thread?

That's the dilemma I'm facing. Even though you do your best to fill all pin holes before priming, there will be some you'll miss and won't see until you apply primer. At that point, what's the best way to to fill them and get long term adhesion?

Thanks

[David-aviator]

Originally Posted by flickroll

David - will that stuff stick long term when applied to either raw fiberglass that uses epoxy resins, and/or to one of the primers that were mentioned in this thread?

That's the dilemma I'm facing. Even though you do your best to fill all pin holes before priming, there will be some you'll miss and won't see until you apply primer. At that point, what's the best way to to fill them and get long term adhesion?

Thanks

I filled quite a few after first shot of primer, that's when many show up. I did it on top of the primer, same technique, sand with 320 paper (actually, 220 will work also) and another shot of primer. I used Nason 2K.

I don't think adhesion is a problem. There really isn't much of the puddy remaining after it is sanded, just enough to fill or cover the hole.

[DanH]

Mike,
Remove the primer, seal the bare glass, sand, re-prime.

Clear Coat is made by System Three, not West. I've been using it as a one shot brush coat to shell small parts; upper leg fairings, emp tips, etc. For large surfaces like pants and cowls you may just want to do three squeegee coats of ordinary West 105 and fast hardener. Either method eliminates pinholes.

Lacquer putty is useful for quick, tiny corrections, like two or three pinholes found after priming. Not catalyzed, so not for large surfaces. And FWIW, Frank F reported his Stewart primer peeled off when applied over putty. I think the thread was back around Christmas.

Flickroll, most builders seem to report multiple shoot, sand, shoot, sand cycles to get all the pinholes when sealing glass with K36. Keep at it.

[RV7Guy]

Quick and dirty process.

1) Before any work, scrub parts with soap and water. Then liberally wipe down with acetone. Hose off and air dry.

2) Sand with course grit paper. This will open up pinhole and voids

3) Hose off and wipe down with acetone again.

4) Dan's method of thinned West Systems will work well. I like to use 30 minute epoxy and micro balloons to speed the process. Brush the thinned epoxy and squeegee in the micro mix.

5) Block sand with a reasonably coarse paper.

6) Clean again then squirt a coat of primer. The pinholes will be evident.
If there is still a large quantity, use epoxy. If they are few, use Rage auto body filler.

7) Rinse, lather, repeat until perfect

I do not recommend the Stanton filler in the tube. It is not catalyzed and is alway shrinking. Additionally, it will react with some primers and paints, creating bubbling.

[David-aviator]

These guys are more up to date with current products and have a better method....follow their advice.

The only paint I ever had come off was over feather fill which was recommended by Burt Rutan at the time, and that was a long time ago.

With the job I just completed, I don't think there is enough spotting puddy remaining to matter if it is done sparingly and only over the pin hole....but what do I know. You'd think if it were so bad, it would be long out of production but it is not, it is readily available. I think it is used in the rehab auto paint world quite a bit.

[David-aviator]

Originally Posted by RV7Guy

I do not recommend the Stanton filler in the tube. It is not catalyzed and is alway shrinking. Additionally, it will react with some primers and paints, creating bubbling.

Just one quick observation, Darwin, I am still getting bubbles (blisters) at rivet heads in my quick built fuel tanks some 5 years since the paint - total epoxy system - was applied by a professional shop. That mystery is still out there.

I do have the parts to build 2 new tanks and one of these days will take on that chore. I do know Kahuna repainted his tanks and the blisters reappeared.

[DanH]

<< Dan's method of thinned West Systems will work well.>>

Naaa, I don't thin epoxy, ever.

<<I like to use 30 minute epoxy and micro balloons...>>

Me too, although for profile and surfacing, chip and heavy scratch fill, etc. Microbubbles are a high bulk, low weight fill additive, a bit too coarse for pinholes. And remember, they're hollow. You cut them open when you sand.

The primary fill additives in commercial body shop fillers are solids like talc and calcium carbonate, one reason they sand smooth.

<<Clean again then squirt a coat of primer. The pinholes will be evident.
If there is still a large quantity, use epoxy. If they are few, use Rage auto body filler. >>

Can't agree with epoxy over primer, but if you'll squeegee off three coats of West 105/205 on the bare glass before primer you won't have more than one or two pinholes per sq ft anyway. For those, a quick fix with Rage, Metal Glaze, Ice, or any other catalyzed filler is certainly superior to an uncatalyzed product.