i'm mostly self-taught in my finish endeavors so i'm hoping someone will be able to help share their experience with me.

i've been spraying conversion varnish and, more recently, 2k poly, for approximately five years. i've used cup guns at the beginning and i've switched to aaa a few years ago. we typically get good results but i don't think i've ever gotten a piece to come out 100% free of any sort of nubs. i've sprayed in front of an open faced booth with dust everywhere and gotten very good results one day (99% perfect, 1% a few nubs - but perfect enough in the mind of our clients) and this-isn't-going-to-fly (we need to recoat it) results the next day. the unacceptable results have been more frequent since i've hired a finisher and i think he and i may have finally discovered why.

with 2k poly, we sprayed a test panel (again, for the 100th time) and finally arrived at some sort of answer. i'm proposing that he isn't cleaning out the gun and hopper (we spray small amounts and have a hopper that feeds our pump) well enough. this seems to be leaving small bits of semi-hard finish in the line and, under the intense pressures created by the pump, work through the filters and end up on the surface of our work. we are using a rebuilt graco merkur 20:1 pump with a kremlin excite gun. we just replaced our 1/8" fluid hose a month ago. we have a micro filter at the base of the hopper, an in-line filter between the pump and fluid hose (at the base of the pump), a filter at the base of the gun, and a mirco-screen at the tip. this seems like a lot of filters for these particles to elude but i this is the conclusion we reached.

last week, we sprayed a section of our test panel with a pps cup gun and another section with our aaa pump. the cup gun yielded almost perfect results while the pump yielded close-but-still-unacceptable results. we used the same batch of finish and shot each piece one after another, as to take material and weather conditions out of play. we're now spraying in an automotive spray booth so we airborne dust shouldn't be an issue.

i think i remember hearing about this theory years ago (semi-hard stuff that can get through the filters and mess up your finish). i'd guess this is the case for us, so my question is how do we effectively clean our equipment and lines?

right now, we empty our lines into a container that we dispose of later. we keep the trigger pulled until the gun starts spraying air. we turn the pump off, load up thinner/acetone into the hopper, turn the fluid back up slowly keeping the trigger pulled into our waste container. once it has cleared the topcoat, we recycle it into the hopper for approximately 30 seconds and call it good. we follow the same procedure when we load up sealer and topcoat.

any ideas? any better way to clean our equipment?

I've had that problem and it was little semi-solid chunks passing through my filters. By cleaning my material container well when l clean up for the day l was able pretty much alleviate the problem.

We take an extra step with our pumps.... we have around twenty+ assorted kremlin pumps with xcite guns.... at the end of the day we purge material out of the pumps and guns.... flush with acetone till everything runs clear. then we purge the acetone into a clean bucket to reuse what is left since it's still a pretty clean. Now we pull/prime polychem acrastrip 600B/G into the pump lines and gun. Every sprayer has a five gallon pail of this mixture and it will last for months since we flush the lines clear before doing so. this will loosen any material hanging around in your equiptment that other solvents wont soften. we were going through a lot of rebuilds on our kremlins because acetone was just not strong enough to clean our pumps/hoses very good.... after a while things would start building up inside them and ruining seals because the material started to form inside them like a calcium deposit..... now if you take one of our pumps apart for maintenance they are clean metal inside... no cancerous residue... in the morning when they get in they pump the polychem back into their bucket.... another clean flush with acetone.. and then pump their daily material for spraying in....

shane -

what are you guys spraying (2k, polyester, what)? where do you get the stuff you recommend?

We spray a barrage of coatings.... Architectural millwork.... We spray anything from pre-cat lacquers, waterbornes, conversion varnishes, 2k poly's & polyester on any given day... just depends what we are working with for the day... I get the polychem from airpower or a local company called M&K international .... you can probably find a supplier through their website here is the link to the product http://www.uspoly.com/600safesolvent.html

shane,

thanks for your help. i just ordered a five and look forward to running your method.

one thing the manufacturer said - he suggested to not leave it in our lines over night. i think the thought was it would remove pre-existing debris and cause problems from this. any thoughts? i'd like to bring things back to new condition and am tempted to ignore this advice. he also said we don't have to run acetone after emptying the cleaner but i'm going to shoot some test panels to see if we can get away with this without any contamination issues.

thanks again.

it will in fact loosen any material than has deposited itself inside your equipment and lines.....Trust me. Leave it in overnight and over weekends and long weekends. At first it may be a pain and you will need to clean all of your screens and mesh filters before you start your finishing process. After this has become your normal flush schedule your equipment will be very well maintained and clean... A quick flush with acetone before you add any of your coating would be the best practice since the polychem is a waterbased product and it could possibly do funny stuff since it has some soap like qualities to it. Besides the acetone will prep you for your waterborne or solvent based coatings....

I do small runs using 2k poly through a Kremlin 10-14 with a 2 qt hopper.

I favor MEK over Acetone for cleaning. I run 3 separate cycles with MEK for about a minute each one and this has kept me trouble free. I can't quite see how any loose crud is getting past the micro filter at the gun unless it is seriously clogged.

I don't know if it relates to you but for years I fought what felt like grit in the 2k topcoat until one day I took the question to my manufacturer/supplier of the 2K poly. He was very familiar with my problem and advised kicking the material pressure up to 50 from 30 which was guidance I had from the equipment supplier. My problem was immediately solved and I have not seen it since, saving me lots of reshooting. Turns out my issue was micro bubbles, not grit. I don't know if this applies for you so take it for whatever its worth to you.