Reducing finish overspray
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Methods, additives and equipment for minimizing this problem. October 30, 2002
Question
I use conversion varnish on my cabinets. We build the face frame and then the cabinet, but we leave the back and the shelves out and spray them separate. We then spray the cabinet, sand with 320 grit, tack, and then spray another coat, then assemble the shelves and put the back on. No matter what, I always end up with a smooth wall and one rough one or one part of the face frame slick as glass and another part rough. I use a cup gun and air compressor, and spray on about 40 pounds pressure. I have tried all different pressure settings to remedy this. Has any one conquered this problem?
Forum Responses
From contributor D:
You can't beat it, but you can reduce it. First, a Kremlin AirMix would certainly help. This is the low overspray champion of the world. If that's too pricey, a good HVLP gravity gun like a SATA or my recommended ASTRO cheapo would also help. If you're using conventional spray equipment at 40 PSI, you're going to have tons of overspray unless you've got a killer spray booth. Also, slowing down the flash of the C-V will help. I like to use MAK for this purpose.
I would suggest two things. I use 3M's fine sanding sponges between coats and that is 150 grit. It may be possible you are not knocking everything down with your 320, especially if you do it quickly and let it get gummy. The other thing I would suggest is a retarder for your finish that allows it to dry slower. A very small amount of Butyl cellosolve does it for me when I have high heat application and need to avoid overspray. I was able to get rid of a lot of that when I finally invested in my Kremlin Airmix MXLT. I don't know the exact science behind it, but I do know with the Kremlin Airmix, the air is introduced into the stream before it leaves the gun, so there is minimized turbulence after it leaves the tip and in return only room breeze drying the product. Whereas, when I was using a pot gun when applying finish, the cloud of overspray that would form was so full of air that was pushing the finish to where it's supposed to go in my eyes dried it to an extent before it ever hit the wood. I say this because so much air was acting on it while it was atomizing, it just seemed dry times were much shorter and overspray much more likely.
From contributor E:
The advice above is very good.
Start with the highest fluid setting practicable so you can move quickly. Using retarder to slow the drying is very important to help reduce overspray. It will also increase the opportunity to introduce runs on those vertical panels, so you will have to develop your technique in order to lay as heavy a coat as possible, just short of producing runs.
Start with the front of the frames, then the top inside, then work down each side, finish with the bottom or deck. Basically, try to work from the front in and from the top down.
Using the bleeder function to blow the overspray out the back as you go will help keep much of the overspray from settling on your work.
Hopefully, there will be very little overspray resulting from your technique, and none on the front of the frame. Use a wrinkled up piece of brown grocery bag to rub out and smooth the minor overspray.
From contributor P:
Since you are already halfway towards flat finishing, why don't you go all the way and finish all your cab panels flat and assemble after done with finish? End of problem! I am frameless and have flat finished for probably 30 years, but it should work as well with face frame.
From contributor F:
What is the best retarder for (SW) CV? I switched from Retarder (butyl cellusolve) to IBIB (isobutyl isobutyrate) for flash-off control on the NC lacquer. Will this work without problems in the CV or should I use MAK or something else? And how much - say 1 1/2 oz. per qt?
From contributor D:
IBIB should work on the C-V, but I'm not certain of it. I've used MAK without incident, so I know that it works - that's why I recommended it. But the IBIB may work fine. I use 4-6 oz per mixed gallon. By mixed gallon, I mean that I always thin my C-V with Xylene 15% and then add the MAK to that thinned mixture.
A better way may be to simply thin using High Flash Naptha (Sherwin-Willams part number for this is R2 K 5 - aka Solvesso 100). This is their preferred method of slowing down the flash off. It also keeps you from needing to play chemist.
From the original questioner:
Contributor P, I thought about your idea, but my only concern is that the glue will not hold as good with the finish already on it. I am considering a new spray system in the new shop, which will be done by November. The HVLP systems that I have seen blow air all the time, even when you're not spraying, but they were cheap. Are they all like this? I really want to go to a system that will not throw a big cloud and without a cup to weigh you down and get in the way.
From contributor D:
Buy an
ASTRO HVLPDX for $85 and that will get you by until the AirMix can be obtained. For the price, this gun is unbelievable.
I like hi-flash naphtha also, and contributor E has it right. It's mostly the order that you spray. You almost always will leave a little overspray with CV inside cabinets even with the backs off. The trick is to leave it in the least obvious place. In this case, the top inside of the box. On real tricky boxes I have been known to keep a cup gun of 50/50 CV thinned with MAK or Hi-Flash naphtha to spray over the whole thing like no-blush for lacquer. The brown paper bag will work, as will the back side of a sheet of sandpaper, but I prefer to rub out the overspray with and abralon pad and a little water or flat lube.
From contributor F:
In warm weather I use the High Flash Naptha 100, thinning the CV about 10% to 15%. Warm in Sacramento is 95 to 100 degrees and very dry. Just right now have a job that wants to be retarded more, and too much thinning and it will start to run. Maybe I'll get some MAK and try that.
I use the Fuhr 355 for my topcoat and I always flat finish.
For the glue joints on my case work, I like to put a scrap piece of stock in the dados. They don’t have to fit real tight, just good enough to keep the finish out. Rack and stack.
Get rid of the cup gun and get an air assist or a pressure pot with a Kremlin HVLP. Part of your problem lies in the fact that cup guns are too slow. You can't lay it on quick enough. The varnish is drying on one side before you've finished the other. With the new gun, you'll save a lot on material and you'll spray twice as fast.
If you want a great finish with faster production rate, pony up and buy an airmix. Believe me, it will pay for itself very quickly.
From contributor E:
It's true that you won't believe just how little air is mixed with the fluid as the Kremlin shoots out its spray pattern. You will have to pick up your application speed and that's a good thing. You owe it to yourself to (at least) get a demo. Kremlin reps love to give demos! There are few products that sell themselves and the airmix is right at the top of the list. If you are sure that you cannot afford the Kremlin airmix, don't get the demo. If you do, you won't be able to sleep at night until you find a way to own one.
The Astro HVLP gravity guns (of which I have three) are exceptionally good performing guns and unarguably the best bargain in the spray gun industry. They are a welcome addition to my finish operation but they are no match for the Kremlin airmix for whole kitchen projects or production finishing. I use the Astros for smaller jobs using post-catalyzed CV's only. Any time I know that I will use more than 1/2 gallon of finish, or where overspray is required to be as minimal as possible, I prefer to mix a larger batch of CV and drop the Kremlin fluid pickup tube into a 1 or 5 gallon pail of the finish.
If you are solely a finisher, the airmix will pay for itself in short order. But if you are like me and are primarily a cabinet builder, finishing only what you build, it will take quite a while to pay for the savings in finish. If you are spraying a pail a week and are now using a conventional (compressed air) gun, you should recover the cost of the Kremlin within a year, in finish product savings alone. Add the labor savings that increased overspray costs you now (face and room filters, labor rubbing overspray from finished work, etc.), and the cost savings quickly adds up. For me, the simplicity of the system, the complete performance, and the quality results were and are worth the expense.
From the original questioner:
I have seen these Kremlin guns and loved them. How much money are we talking about? The one I saw was 2,500 with an air dryer. I do want to get rid of the cup gun. I don't think I would like the gravity guns - they look too awkward.
From contributor D:
That's about right for the list price on a Kremlin 1014, but it depends on what brand and model air dryer it comes with.
You may not need an air dryer (per se). You will need a water filter at least and a good one such as the Sharpe filters that differ in price, depending on size and filter capacity. Set up your air lines properly and locate the filter as far downstream as possible, with a short line (15 feet or less is good) from it to the airmix pump and you should be fine, particularly if you are not a full time (40 hour per week) finisher.
Don't forget to check into the agitator for mixing your finish and keeping it in suspension while spraying. It ain't cheap but definitely worth the expense, in my opinion. Oh yeah, make sure you get Kremlin to throw in a bottle of pump and gun lube and a pack of seals and tip cleaning needles and such that you will need to keep your gun serviced and running well.
