Spraying nitro lacquer - weird small, hard white specks

[Mike Dowell]

I've sprayed nitro lacquer a lot. But, today I noticed something weird, something I've not seen before. After spraying, there were a few small, hard white specks in the finish. They are super hard, like cured lacquer but I don't know where they came from. You can almost not even scratch them off with your nail. They weren't there prior to spraying. They can be sanded out but I'm wondering if anyone else has had this issue and what the cause of it was? I pour my lacquer into the spray cup through a paint strainer so I'm really confused as to what this is. Was it a contaminate in the cup and got sprayed out? Is it some weird reaction once sprayed?

This is Nitro lacquer which is thinned and sprayed through an HVLP sprayer.

Any thoughts?

[John Coloccia]

It could be the gun spitting. Make sure you're not getting any leaking around the packing...you know, disassemble, make sure it's lubed, etc.

[Mike Dowell]

Its brand new and I changed the needle to a smaller one so I know the nozzle is snug with a washer, etc. Is that what you mean?

[John Coloccia]

I mean where the needle passes through the body of the gun. It usually goes through something that looks like a nut. In there is this fiber like material called the packing. That seals around the needle. If that's leaking, you'll get what's called "spitting", where instead of laying down a nice, even flow of material, it will shoot out these heavy, little clumps here and there. That packing usually needs to be lubricated with spray gun oil, and occasionally replaced. Sometimes the nut comes loose too. Now that you say you replaced the needle, it makes the packing all the more suspicious. There's lots of potential problems, but it usually ends up being this because most people know enough to double check the more obvious things

Typically you put a little lube, then tighten it until the needle starts to bind. Then just back it off until it's smooth again.

It's hard to tell without seeing it in person. It could be foreign matter too. Maybe it's just my screen, but it just looks like little clumps of dried lacquer from here. Does it scrape off at all?

[Jay Gargiulo]

Mike, I've had the same problem before and came to the conclusion that it was from dried lacquer in the bottom of the cup. I took 5 or 10 minutes and gave the cup and the gun a thorough cleaning and the specks went away. After that I was much more diligent about keeping the set up clean since those things are a bear to sand out and even then, you need another speck-free coat to go over the top.

[Mike Dowell]

I'm going to check that packing this morning. I wonder if it was contaminated after all. Funny that this has never happened before but then again, that's how coincidence works. I'll check the packing and give a good cleaning and we will see how it goes!

Thanks!

[John Coloccia]

re: dried lacquer in the cup
I wouldn't spray without using either DeKups or the 3M PPS system. I have DeKups, but in retrospect I think the 3M system is a little nicer. Once you try it, you'll never go back.

[Rick Mosher]

If this is a satin or lower sheen of finish it probably is dried out flattening paste. You can find out where it's coming from by dropping a little on a clean sheet of glass and letting it dry. If the white spots show up it is contamination in the lacquer, if not then there is something in your gun or air lines.

[Mike Dowell]

This problem is not happening any more. Unfortunately I don't know how I solved it. I cleaned the gun out and the cup, and also I've since started doubling up on the paint strainers. I still think I'm going to get that 3M system.

Thanks!

[Mike Dowell]

I mean where the needle passes through the body of the gun. It usually goes through something that looks like a nut. In there is this fiber like material called the packing. That seals around the needle. If that's leaking, you'll get what's called "spitting", where instead of laying down a nice, even flow of material, it will shoot out these heavy, little clumps here and there. That packing usually needs to be lubricated with spray gun oil, and occasionally replaced. Sometimes the nut comes loose too. Now that you say you replaced the needle, it makes the packing all the more suspicious. There's lots of potential problems, but it usually ends up being this because most people know enough to double check the more obvious things

Typically you put a little lube, then tighten it until the needle starts to bind. Then just back it off until it's smooth again.

It's hard to tell without seeing it in person. It could be foreign matter too. Maybe it's just my screen, but it just looks like little clumps of dried lacquer from here. Does it scrape off at all?

Incidently, the packing nut was not tight at all! This wasn't the problem in the end but out of curiosity, what sort of issues arise from loose packing nuts?