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How to Keep HVLP Sprayer From Hardening Up In Between Coats

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Forum topic by qball posted 01-12-2012 10:13 PM 4966 views 0 times favorited 9 replies Add to Favorites Watch
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qball

49 posts in 1880 days


01-12-2012 10:13 PM

Topic tags/keywords: spraying poly varnish lacquer shellac

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?


9 replies so far

View Bill Davis's profile

Bill Davis

226 posts in 2678 days


#1 posted 01-12-2012 11:09 PM

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.

View Bill White's profile

Bill White

3589 posts in 2714 days


#2 posted 01-12-2012 11:44 PM

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

-- bill@magraphics.us

View dbhost's profile

dbhost

5387 posts in 1986 days


#3 posted 01-12-2012 11:53 PM

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

-- My workshop blog can be found at http://daves-workshop.blogspot.com

View StumpyNubs's profile

StumpyNubs

6272 posts in 1554 days


#4 posted 01-12-2012 11:59 PM

Try shrink wrapping it. Maybe buy a Foodsaver!

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

-- It's the best woodworking show since the invention of wood... New episodes at: http://www.stumpynubs.com

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Halfday

4 posts in 1667 days


#5 posted 01-13-2012 03:38 AM

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.

View ScottN's profile

ScottN

261 posts in 1434 days


#6 posted 01-13-2012 02:51 PM

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

-- New Auburn,WI

View 404 - Not Found's profile

404 - Not Found

2544 posts in 1723 days


#7 posted 01-13-2012 07:22 PM

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.

View willie's profile

willie

465 posts in 1208 days


#8 posted 01-13-2012 07:40 PM

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.

-- Every day above ground is a good day!!!

View CampD's profile

CampD

1217 posts in 2240 days


#9 posted 01-13-2012 08:04 PM

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.

-- Doug...

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