Storing A Spray Gun Between Coats

[Ken Krawford]

I have a turbine driven HVLP sprayer. I've been priming some cabinets with Zinnsers BIN shellac based primer. Quite often I will shoot a coat late at night and a follow up coat the next morning. In the past with water based finishes I would soak a cotton ball with water and lay it over the air cap and then wrap tightly with a piece of aluminum foil. This worked fine. After doing this for a couple of days with the BIN product my gun was a gooey mess.
In a couple of days I'll be applying the finish coat which is a pre-catalyzed lacquer (Lenmar).
What does everyone do with their guns between coats? The thought of completely cleaning a gun between coats doesn't sound too appealing but better than dealing with a clogged gun.

[Jim Becker]

I only use water borne and while I'll spray a whole day without emptying the gun, I don't let it go overnight. (I could, but I don't) For shellac...and you BIN is shellac based...I spray and clean when I'm done since recoat time is very fast. You don't need to wait hours in my experience to get your coats on. What you need to do for the various products you are using is to understand the recoat timing and use that to "schedule" your spraying sessions. Shellac and (solvent based) lacquers have recoat times measured in just a few minutes in some cases. Waterbornes are a little longer but still measured mostly in minutes.

Be sure you also are using a primer/sealer that's known compatible with whatever comes next. Use the BIN if it's hiding properties are necessary, of course...

[Paul F Franklin]

Several folks here have mentioned in other posts the 3M PPS system, Jim B. and John T. among them. One of the nicest things about that system is that it is takes less than a minute to switch from the material you are spraying to an appropriate solvent, water, alcohol, whatever. So I make it a habit to do the switch and spray some solvent through the gun anytime it will be longer than an hour or two before I will be spraying again. And I wipe off the tip of the gun. Then at the end of the day I disassemble the gun and clean it. I'm sure this is overkill, but I've never had to deal with a clog or poor gun performance because of dried finish somewhere.

[John TenEyck]

Ken, I read your post to say that you used a water soaked cotton ball over the end of your gun that had BIN shellac based primer in it. Is that correct? If so, no wonder you had a sticky mess. BIN is an alcohol based product and completely incompatible with water. I've sprayed a lot of BIN white shellac based primer. I remove the air cap between coats and soak it in DNA or lacquer thinner, and I wipe the nozzle tip with the same solvent. BIN can be recoated in an hour or two at the most, so I try to do so. If I have to wait more than an hour or two, I open the PPS cup and stir the contents before spraying another coat because BIN settles out pretty quickly.

One trick I've found is that the PPS cup plugs also will seal the inlet to my spray gun. If I have to spray for more than one day I remove the PPS cup and put a plug in the cup outlet. I remove the air cap and clean it. Then I flush a couple of ounces of solvent through the gun, wipe the nozzle clean, refill the gun with solvent and plug the inlet with another plug. The next day I tip the gun nozzle down and pull the trigger to drain out the solvent, then proceed with getting ready to spray. This works fine for any non post catalyzed finish.

Also, Ken, I really like BIN but I like Lenmar's Undercoater even better. It's WB so cleanup is easy, it dries quickly, sands beautifully, and is CHEAP. I paid about $40/gallon the last time I bought it. BIN is better for stain blocking, but as a white primer Undercoater is great.

John

[Rich Engelhardt]

In the past with water based finishes I would soak a cotton ball with water and lay it over the air cap and then wrap tightly with a piece of aluminum foil. This worked fine. After doing this for a couple of days with the BIN product my gun was a gooey mess.

Switch to using ammonia instead of water - for both.
Ammonia cuts both shellac and waterborne materials.
Just don't thin or reduce either with it.

[Ken Krawford]

Thanks everyone for your feedback. Much appreciated. John, you missed the first part of my sentence that said "... with water based finishes I would soak a cotton ball". I was using 50:50 ammonia:water for cleaning as directed on the BIN label. It left a lot to be desired. Next time I'll use it full strength. I didn't realize it was good for water based finishes too.
John thanks for the heads up on Lenmar's Undercoater. Love the fact that it's water based.
I was priming parts of this project as I finished constructing them. Now that everything is built I think I can shoot everything in a couple of sessions. It's been a long time since I've use solvent based lacquer. I'm not crazy about the odor and clean up but LOVE how fast it dries and cures.

[Jim Becker]

Ken, if you are going to spray solvent based lacquer, you need to either have a proper spray environment in your shop (pro level with explosion proof ventilation) or do it outside. This is in addition to PPE for you. The stuff is dangerous and must be used with safety in mind.

[Marc Fenneuff]

Off-topic, sorry, but what are you guys using to drive your PPS guns? The system is appealing to me but my compressor can't do close to the required 10CFM at 20psi - at least I don't think it can. My 30Gal compressor is only rated for 6.4SCFM@90 and 8.6SCFM@40. I'd be spraying small machine tool parts with an oil-based paint. I had bought a Devilbiss HVLP touch-up gun to do this spraying and have plenty of CFM for that gun, but the cleanup seems a bit daunting (I've never sprayed with a gun before).

[John TenEyck]

Off-topic, sorry, but what are you guys using to drive your PPS guns? The system is appealing to me but my compressor can't do close to the required 10CFM at 20psi - at least I don't think it can. My 30Gal compressor is only rated for 6.4SCFM@90 and 8.6SCFM@40. I'd be spraying small machine tool parts with an oil-based paint. I had bought a Devilbiss HVLP touch-up gun to do this spraying and have plenty of CFM for that gun, but the cleanup seems a bit daunting (I've never sprayed with a gun before).

Mark, several of us are using PPS cups but not on an Accuspray gun. I use a Qualspray AM-6008HVLP gun, from Homestead Finishing. It takes 10 cfm at 40 psi. But they also make the same gun in an LVLP version which only requires 6.5 cfm. Your compressor should be able to drive that gun w/o problems. Both guns are offered with a conventional bottom feed metal cup or with a PPS cup. The PPS system is the one I'd recommend regardless of what gun you use. Clean up is so simple, or you can save unused finish in the PPS cup for future use and just clean the gun.

You should be able to put a PPS cup on your Devilbiss gun. Go to 3M's website and look up the correct adapter tube for your gun.

John

[Marc Fenneuff]

You should be able to put a PPS cup on your Devilbiss gun. Go to 3M's website and look up the correct adapter tube for your gun.

John

Ok, that makes sense! I found the adapter list, most places showed out of stock on the one for my gun, but I was able to place an order at one shop so we'll see what happens. I'll work on getting the cups next. Many thanks.