# How to Keep HVLP Sprayer From Hardening Up In Between Coats



## qball (Nov 3, 2009)

When spraying poly, varnish, lacquer, shellac ect. with a HPLV sprayer how do you keep the sprayer from hardening up between coats? Some of these take some time to dry in between coats and cleaning out the sprayer in between every coat is not that efficient. Any advice?


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## wmodavis (Aug 28, 2007)

Sorry I can't speak directly to the HVLP spraying but will tell you what I do with my regular (i.e. non-HVLP)
spraying.

First off I mostly spray lacquer but have sprayed poly and regular varnish. For curative finishes as varnish I clean out the sprayer unless I know I'll spray the rest before it cures in the cup and plumbing. An advantage of using evaporative finishes is that there is not the long time required between coats so it is practical to apply many coats over a day or more time frame.

With lacquer, which is an evaporative finish, I have left lacquer in the sprayer cup for up to a week if there was enough left to not be too much waste and I would spray more relatively soon.

The key to leaving it in is to not leave it in the plumbing - just in the cup, then it sits there as if you poured it back into the original can or a jar or something. If it hardens in and plugs the plumbing it is much more difficult or impossible to clean out. To get the finish (or most of it) out of the plumbing I release the pressure in the cup and cover the nozzle with a rag held sort of tightly in place with my hand cupped over it and trigger the sprayer to only pass air. It will then force air backwards down the finish carrying plumbing to shove the finish out of the plumbing back into the cup and I hear it bubbling in the cup. I then just let set til I am going to spray the rest of the finish. The fluid passage is now open and will allow the finish to flow through the plumbing next time and in the process disolve the bit of finish in the plumbing that didn't blow back to the cup but hardened. This procedure also works with shellac which is also an evaporative finish

For finishes that harden by curing (varnishes) rather than evaporating, the above procedure is more risky and the time it is left in the plumbing and cup must be shorter or the cleanup of cured finish will 'cure' you of leaving it cuz new guns are costly.

I just refuse to sacrifice my pricey Binks gun by risking leaving varnish in. I'll pour it back into some container and run solvent through the system to clean it out. I don't think it's all that bad to do.


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## BillWhite (Jul 23, 2007)

Clean it every time unless you're gonna recoat real soon. Sorry. Its just the way I was tought when all we used was NC lacquer on pianos. Takes some extra time, but keeps the "OOOPS" outa the process.
Bill


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## dbhost (Jul 20, 2009)

Clean it. I know it takes time, but the alternative stinks…


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## StumpyNubs (Sep 25, 2010)

Try shrink wrapping it. Maybe buy a Foodsaver!

(The greatest woodworking show mankind has ever known is now online!)


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## Halfday (Jun 4, 2010)

I have a bottom cup HVLP gun (Fuji Q4 Pro) for which I bought several extra quart cups. Between coats I simply remove the finish cup, wipe down the pick-up tube (probably not necessary), attach a spare cup with solvent, and spray maybe a half-pint through the plumbing. Takes only a minute. Gun is the ready for the next coat. Fuji also sells some inexpensive orange plastic cup caps to block any dust or other contaminents from entering a cup with material in it. Not to argue with a previous poster, but Fuji cautions to never cover the business end and squeeze the trigger.


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## ScottN (Jan 24, 2011)

I have an old tooth brush I use. I dip it in the cleaning solvent and clean the end of the tip off.


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## renners (Apr 9, 2010)

What kind of system do you have? I have never had any issues leaving lacquer in the gun overnight, it's just like being in a sealed container, so it won't dry. I wipe off the tip of the nozzle and leave the aircap soaking in thinners until the next coat. If I know I won't get to spray more coats the following day I clean it out.


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## cjwillie (Sep 6, 2011)

The only times I ever had any problems with finish getting hard in the gun was with catalyzed lacquers. You could extend the time it stayed liquid by putting the gun in the refrigerator between uses. This would work overnight but not sure how much longer it would extend working time. Plus it had to be brought back to room temp to use.


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## CampD (Nov 8, 2008)

What renners said,
I leave oil poly in the gun over night just disconnect the gun from the air source
and wipe down the nozzle before starting.
I've left latex enamel over night to with-out a problem.
Just need to clean the tip.

Cat Lacquers I clean the gun at the end of the day by pouring the Lacqure back into a clean sealed 
container and run Lacquer thinner through it and leave just enough thinner sitting in the gun 
to cover the filter, rinse and give it a quick rub down in the morn and your ready to spray again.
(Learned this from a buddy who paints cars professionally)

When all finishing is done, thats when I completely disassemble the gun and clean spotless.


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