How long can I keave finishes in the spray cup between coats?

[Gregory of Sherwood Forest]

I now have 3 different guns, two are regular SS, and one is a PPS. How long can I leave various finishes in them between spraying coats? I've been unable to find much info on this in any of my references.
Latex?
Acrylics?
Stains?
Polyurethanes?
Water based?

Thanks in advance!

[fredhargis]

I've never sprayed varnish or latex, but for the others I don't worry about leaving it in the gun between coats on the same day. I won't leave it overnight, tho. I was at a WWing show where the Apollo demonstrator told the crowd he would leave the varnish he was using in the gun the entire weekend without cleaning it until they closed the doors....I don't have the nerve. I will sometimes (with the waterborne and acrylic finishes) remove the air cap and needle and clean them between coats...depending on how long I have to wait. I usually do that if I have more than a few hours between coats.

[jteneyck]

I think the answer depends upon your gun and the product you are spraying.  Some finishes seem to react with the gun materials and won't spray well after an hour or two.  In that case, you need to clean after every coat.  And some finishes will settle pretty quickly, like a thin product with a lot of flatters in it, so you have to at least stir the product in the cup and spray enough to clear the gun before spraying the next coat.  Often, it's just better to clean out the gun and start fresh.  For all other cases, I follow what Fred said and only clean the gun at the end of the day, and the air cap and end of the needle after every coat.  I only spray WB products and shellac.  I know some guys who spray solvent based products that spray the same product every day, and never clean out their guns.  

John

[Kansas City Fireslayer]

Greg,

I don't think you'll have any problems leaving acrylic latex in the gun for the majority of the day.  I'd wipe the tip and cap clean with a wet rag in-between shooting.  Check your fan and pattern on cardboard before putting it back on your project just in case.  The gasket seal and tip will keep it tight enough to where air won't affect it that much.  Definitely clean at the end of the day.  I've left GF waterborne and BM Advance in my gun all day with coats spread out over 3-4 hours.

[Gregory of Sherwood Forest]

Thanks Fred and John.

My first multi-day spraying projects will be white paint for the bathroom doors, cabinets, and trim. It'll probably be a 4 day job as I have 3 bathrooms worth, and my makeshift spraying tent won't hold much at a time.

I was hoping to leave the paint in the gun between coats, maybe 4 hours sitting, tops. Overnight full washing out.

Does the PPS have an advantage in this? I'd think that with little air in the system, the paint should be good for several hours at least. Just a guess, as I have no practical experience.

[Rob Young]

I have been using a pressurized cup-under gun.  And inside the cup I'm using the cheapo cup liners from Harbor Freight.  Other than discovering one bag did not have a seal on the bottom (now I blow into each bag before putting in cup) I've not had an issue with any reactions to the aluminum cup.

The liners make cleanup pretty easy but I may have more waste as it is difficult to get all the material back out of them either spraying or pouring back into the cans.

Gasket seals well and I've had no issues leaving shellac, water-borne poly or "latex" paints in the cup for up to 1/2 day.  However I am de-pressurizing the gun by pulling the hose.  Then I hold back the trigger for a few seconds to (I hope) drain the tube.  And finally wipe the tip with a rag.  Also, since I am using my driveway as the spray booth and it was dang hot the last time I did this, the gun rested in the garage where it was at least a little bit cooler.

So far, no serious problems.  I did notice that there was more build-up around the nozzle using the acrylic and enamel latex paints but I believe this was from spraying, not from "resting".  Regular wiping with a damp shop rag took care of the build-up.

But also haven't had any projects run longer than about 1/2 day.

[Stwood_]

I never removed the lacquer from my guns. But, ya'll are running different guns now, and I used lacquer every day or every few days.

[Snipe Hunter]

Forever, unless it's catalyzed or in a gravity feed gun. It's one reason I don't like using gravity feed guns. My clearcoat gun is gravity feed so I clean it after every use and throw out the remaining catalyzed clear.

For paints, I squeeze the air out of PPS cups and cap them. Put them on the shelf and stir them again when I use them.
But you have to keep the gun clean because he finish will dry around the tip.


I leave my primer in my gun all the time. Honestly, I think I've cleaned that gun 4 times in 10 year with daily use.