TexasAirBoss

My Feedback: (22)

I keep shooting my fiberglass cowl with primer and getting pin holes in the dried paint. I sand the primer back down and shoot it again. The pin holes come back. What am I doing wrong ?

Superchipmunk91

did you make sure you cleaned the cowling good before you sprayed it, i had the same thing happen to me and i could'nt figure out what was going on so i completely sanded it down smooth and cleaned in with alcohol and it was fine after that.

Live Wire

What painting system are you using If you are using a compressor with conventional gun it could be what we call fish eyes caused by oil in feed line[:@] Not using a filter to trap oil and water in the lines.

TLH101

My Feedback: (90)

If it's epoxy, it's probably pinholes. You need to shoot on a coat of primer, and sand. Next get some "glazing & spot putty". I uase a singledge razor blade and spread it over all the pinholes. Now sand with 400 grit and reprime. May take a couple of applications to get all the holes.

Don41

Hmmmm. I just recently decided to drop Monokote in favor of cloth and paint. You're not helping to reassure me as to the wisdom of my decision (:-).

saramos

With cloth covering, the big issue is filling the weave. For that, I use a high build sandable primer. Pinholes are not much of an issue.

Pinholes are common with molded models and parts. Primer will often bridge over the holes without filling them. After sanding, the holes are back. For this, use a spot filler. BVM makes a filler that works well, but is a bit on the pricey side. I use an automotive spot filler in a tube from the local auto parts store. Sometimes, applying with a squeege from different directions and multiple applications are needed to fill the little buggers.

Scott

Ed Smith

Unless painted in the mold, molded fibreglass parts will always have pinholes. They have to be filled before primer or any paint is applied.

The easiest and cheapest way to fill them is to use drywall compound. I believe it is called sheetrock mud in the US. It is available from builders supply stores. The smallest tub is about $6.00 and would last a life time if it it not go hard after a year.

This is the way to us it. The glass components must be ready to prime. Scoop up a blob of compound on the end of your fingers, dip it into some water and very firmly rub it into the fuselage. Force the compound into all of the holes. Leave for 24 hours then DRY sand with 120 grit. Remove all of the surface compound. It is now ready to prime. Absolutely do not wet sand after this process.

I have been using this method for years. It is quick, cheap and easy. A fuselage as shown in the picture took just minutes. For size comparison that is a 14" prop.

Ed S

carlgrover

Put on one coat of primer by hand with a brush. Look at the cowl and see if any pinholes form. If they do, scrub the brush over them a little bit to break the surface tension and fill them in. Don't worry about brush marks, they will sand out easily enough. After the primer is dry, you can sand and should be able to shoot it with a gun. The pinhole problem should disappear. I've done many this way and have no problem with pinholes. I also usually brush the first coat or two of primer on prior to switching to a gun.

Carl

TexasAirBoss

My Feedback: (22)

Its been a while since I shot that first coat of primer. And it did sand off mightly easy. As I recall, it did occur to me that I had not cleaned the cowl first. I had "go fever" and just forgot.
But now, the problem is that I can't get all the primer to sand off. Half of the cowl has great adhesion. But half was full of pin holes and that half sanded off pretty clean.
So, I think I can clean the half that is bare fiberglass and then re-shoot that half. Sand and then another coat to insure its all even.

LATER I ADDED THIS :

OK, been sanding that primer off and guess what. The holes are in the fiberglass cowl. Big-Uns, as AL Bundy would say. No wonder. I do think a few were caused by not cleaing the cowl correctly, but some are just simple crators.