Spray Finishing Question

[Ruffnek]

When spraying a finish like lacquer that dries fairly quickly, do you clean up the gun between coats?

[Stretch]

Short answer: No. ;D

[jim@jlazy3]

Cody, I'll go all day with out cleaning the gun between coats. I do find it necessary to 'scrub' the tip/nozzle with a toothbrush dipped in lacquer thinner occasionally, but that's all.

[TDHofstetter]

If your pot is closed, the only place the lacquer can dry is right at the tip of the tip, where the needle shutoff is, in the nose of the gun. The action of pulling the trigger pulls the needle back out of the opening so it'll spray immediately. Subsequent coats at normal recoat intervals can use the same potful of lacquer with no problems. Hang it up, but don't clean it up... that'll save a bunch of thinner, too, and some small amount of lacquer.

Pot open or pot closed, lacquer will dry some overnight, though, and start to go critical inside the gun. THAT is what you very much DO NOT want. If ya let it go too far, you've gotta' soak the gun in stripper.

[jim@jlazy3]

yup, now conversion varnish...that's a different story

[art3427]

The real problem with non-catalized lacquers is having materials dry in the hoses. This happens when the system is about empty. As long as the hoses a full from pot to needle there shouldn't be a problem. However, if you plan to put the gun away for a while I'd suggest flushing the system with thinner and leaving enough to keep the hoses filled. Of course, if you are using a cup gun, this will not be necessary. Just flush thoroughly with thinner and put it away. Always rinse thoroughly when using catalyzed finishes.

art

[Ruffnek]

Thanks for the answers, guys.

Stretch, I liked yours best. ;D

[Stretch]

Feb 8, 2010 9:45:12 GMT -6 Ruffnek said:

Thanks for the answers, guys.

Stretch, I liked yours best. ;D

Thanks! ;D

If you need any hands on help, my shop is up and running, and I'm set up to spray now. You know how to get a hold of me.

[Joe Lyddon]

I've often wondered the same thing... I'm glad that Cody finally asked the question... Maybe I'll try spraying someday...

I have a few dedicated spray containers that hook up to a compressor. Don't know how they work, if they work, etc.

I was wondering... To get the 'feel' of it, could one put plain ole water in the can & play around with adjusting & diddling around getting patterns & how to change them, etc.??

Then put something else in the can... like Shellac, etc.

I was shying away from spraying because I didn't want to keep cleaning equipment after every coat! I thought it was a waste of time for small jobs like I do! ;D ;D ;D

Is there a max amount of air that should be pumped into those cans?
Would the air that normally goes to a brad nailer be sufficient to handle spraying?

Thank you...

[TDHofstetter]

Joe, use either mineral spirits (slow evaporating) or lacquer thinner (fast evaporating)... or even straight acetone (evaporates like LIGHTENING) to tweak up the gun. Nothing to clean up afterwards that way, and pretty much every gun on the market can handle the crazy solvents. Not every gun can handle water (rust issues). Use denatured alcohol to adjust a gun for shellac.

Do the final adjustments with the actual finish being sprayed, 'cause it won't act exactly like the solvent did.

The other thing... for spraying, you really need a water/oil separator in the air line, as close to the gun as you can reasonably get it. If you mount it back at the compressor, some water vapor will get past it and condense on the inside of the hose. You'll get water in your finish, and it'll look like crap.

[Ruffnek]

I spray some WB finishes like Target's USL and even Minwax WB poly. For those, I clean up with water and soap so I don't see why you couldn't use water to adjust the spray pattern.

For Shellac, definitely use DNA but use caution with it. That's an extremely flammable medium to be spraying.

For lacquer, like Tim said, use lacquer thinner.

For other oil-based finishes, use mineral spirits or naptha.

FWIW, I haven't been cleaning my cup sprayer between coats but wanted to see how the "pros" did it. ;D

[TDHofstetter]

Depends on the gun. Some guns have stainless-steel or brass needles to regulate the paint/finish flow. Some don't - the needles are made of some non-stainless steel (probably 12L14 or something else that machines easily), and if they're exposed to water or water-based finishes, they'll rust.

[Ruffnek]

Well, hopefully all the ones sold in California are brass or stainless tips. Since they have banned solvent finishes I'd expect they spray a lot of WB finishes.

I guess I got lucky because neither of the cup guns I use have rusted tips and I spray WB finish and clean with water and Dawn detergent. One of them is an old Sharpe gun and the other is the Wagner conversion gun. I used the Sharpe to spray paint my house.

[deepsplinter]

Does this "no cleaning between coats" apply to pre-cat lacquer, too?

If I'm spraying a shop full of doors and drawers, it might be 2-3 hours between coats.

[TDHofstetter]

It applies to anything that doesn't require mixing with a hardener or catalyst. Anything that gets mixed with hardener or catalyst will set up in the gun because it doesn't need air to cure. Anything that doesn't get mixed with hardener or catalyst, only with thinner/reducer, is fine to leave in the gun for a couple of hours... as long as the gun's closed and it's not a pressure-pot type gun that's kept full of pressurized air. THAT may set up a little.

[Mark T]

I have always taken a tiny scrap of plastic wrap and stuck it on the gun nozzle. Not wrapped, just a tiny piece. It will stick just fine. This seals the opening from any air. No air, no dry... for a long time. I do this same trick with all paints, like between coats to the cars.

Water should work fine for pattern testing and learning, but I like solvents better simply because I can spray the same area almost immediately. Solvents flash off quickly, leaving a clean surface again and again. I mostly use my block wall. Easy to see on the gray wall.