Thanks for sharing the useful tips!!

Any little tricks or tips to help get round one of the most annoying awkward problems in composites is a bonus!!

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I've found that diluting clear down A LOT gets it into the pin holes.  I dilute with equal volume to spray but 2 volumes for pin holes.  I brush this on and really work it in to the pin holes.  3-4 coats like this (30 min dry time) and then I can flat and spray.  I've found no need for the aggresive needling this way.  Its all about sealing the holes IMO.

This is my guess. Yes the alcohol evaporates slower so it gives you time to blast the gunk out.

Two things can cause the clear coat not to go into the holes. (I assume everyone has sprayed clear and no matter how thick you go it will not settle into the pinhole craters. Its like a reverse magnet!

1. Grease, silicone or even the alum blush that develops at the surface of the epoxy part during cure, can repel the clear coat . So if you sand and wipe the part down you will not remove this contaminate from the bottom of the pinhole craters. The pin action I described not only opens up the pin hole but also roughens up the walls of the pinhole like sanding. The alcohol bath and air blasts the residue out.

2. The second thing that can repel the clearcoat from going into the pinhole is static electricity. I read some where that people who paint Corvettes or plastic bumpers use this trick to eliminate static.

Fred

 

I have heard this from an experienced guy before, he used to rub some sort of clearcoat with his fingers into the opened up pinholes. Never actually tried it myself, it's good to get some confirmation.

Regarding the alcohol, I assume because it's less volatile than acetone which evaporates too fast. Fred is literally washing the gunk out of the pinholes with the alcohol and compressed air. More aggressive solvents might attack the sanding dust too much, making it swell and get trapped in the pinholes?

Interesting. Any reason why pure alcohol and not Acetone? 

I have finally got a technic to fill pin holes in one shot that I will share with the group.

1. Sand your part with 220 paper.

2. Wipe down with pure Alcohol not thinner or prime wash or acetone.

3. I have a large needle (4 inches) and have flattened the point just a bit.
    At ninety degrees lightly push the needle into each and every pinhole and twist.
    (this opens and scores the pinhole)

4. Wipe and rub in the alcohol again, very wet, blow dry with high pressure.

5. Mix a small batch of automotive clear and brush on the affected area. (a good thick coat.)

6. Now with a gloved finger rub the clear in with circular motions. (be aggressive)

7.Now brush another coat of clear on right away. Wait 10 minutes and brush on another coat with what you have left over.

8. I then put the part in my hot box at 110 f over night.

9. Flat sand with 220 grit. BANG the pinholes are ALL gone!

10. clear again with your spray equipment and you are ready to wet sand and compound.

NOTE: I have posted this technic because it works. I used to have to go over a part sometimes 4 times to get rid of all of the pinholes.

If you are a professional Auto Body painter this will sound barbaric, but you can't argue with success.

Hope this helps.

Fred