We all run these businesses where everything is figured out down to the smallest detail, no surprises, using a system it took years to develop. Then the product goes into the spray booth. This is where the real magic happens; the finish can make or break a project. Well, my finisher (witch doctor) recently quit, so I figured I would go in the booth, so if this happened again I would have a backup on short notice. Was I surprised! After making a call to my paint supplier, it seems we had been doing it totally wrong for years. I mean prepping it, mixing it, spraying it, everything all wrong!
So being the good cabinetmaker, I figured I had better learn this, and quick. Unfortunately, finishing is not a trade but rather witchcraft. There are no rules. The cup one uses to check has no markings, it could be a zahn or a ford or a number three or two, who knows. The one my supplier gave me a dozen years ago was the wrong one and his tech sheets only say DIN so many seconds.
Now to the gun settings - you guess, you just guess. There is no "so many ounces per minute," more like the stream will drop off in three or four inches. Really? Then there is the air pressure to the air cap, measured not at the cap but rather from the pot before the hose and a venturi, once again voodoo.
The booklet that comes with the gun was written about a gun that has been outlawed and the people who sell it are exactly that, sales people.
(Business and Management Forum)
From contributor L:
There are so many different variables in finishing it is hard to have markings on anything that would make sense in all conditions. It is mostly done by sight and feel. After you get used to it and know how things work, you don't need the viscosity cups. You can see how thick it is by how it flows off of your mixing stick.
Adding thinners and retarders are environment sensitive and you have to know how the different systems you use will be repaired by the different conditions. It is very doubtful that your finisher was doing everything wrong, as there are quite a few ways to approach finishing. And each and every finisher will have their own secrets.
I do some things that are different from some others. When using a shading lacquer, most will have a sealcoat on the wood already and I put it right over stain. It is different, but it is not wrong. It works for me. If your finisher put out a nice product with little or no issues, obviously he was doing something right.
You can't learn finishing from a book. You can be told what to do by said book, but without doing it in person on real samples, you won't know how things react and interact.
It is not so much about the paint mixing anymore. I talked to my rep and have that somewhat down, although he did say I should get a weather station, barometer and such as he was walking out the door. Once again voodoo. Should I be checking the phases of the moon?
The gun settings are the problem. I have checked all over the internet and there is no one good method for measuring. If I chucked a gun in a jig, put a pressure on some paint, it would create an exponential function, measurable and repeatable. Or I could just pee it into a measuring cup with a stop watch. Once again, I can do something with this, but alas if the internet knows nothing of this, then a wizard is involved!
Take a piece of large paper and tape it to the wall. Take your gun and give a short burst of finish on the paper. What does it look like? Normally, what you are looking for is a very skinny ellipse. You want a nice even layer of finish over the whole ellipse. Spray it a bit longer and see how it drools. Is it drooling the same in all spots? If yes, it is setup pretty good. You need to play with all the different settings until you get a nice shaped even coated area.
If the atomization is not fine enough, you probably need to thin it some more. It you are getting tails on the edges, you need to have more air coming out of the cap. If it is heavier in the center, you need to push the needle in more so less material comes out, or thin it more.
Like I said, you need to play an awful lot to get the hang of it. Just because you went in there and he was swinging the gun back and forth effortlessly, doesn't mean it isn't hard or isn't an art form, because it really is.
Generally the better the finish, the harder it is to learn. But once you figure out a finish, you will be able to master it easily.
As for mixing, I use my mixing sticks to mark the ratios before I open the cans. I simply eyeball the ratios on the stick using the height of the mixing cup as a reference. Very accurate and mostly idiot proof. It works well for complex multi-part finishes.
New way, a lot more material, not as hard, clogs the filters, slower drying time, is either more gloss and shows imperfections or has more imperfections and it takes longer. The only issues with the old way, it smelled like acid for a few days, it was wrong and it was witchcraft.
I know what you mean by practicing and experimenting. In fact the people that were in there for the last ten years had created a Frankenstein Monster, but everyone loved it, got complements for years on how flat it looked. If I went next door to the display the other guy did, mine looked way better, but I digress - my aim is to paint a finish like the supplier made the product for. This involves using scientific method and finishing requires pixie dust.
Oh, the stick in the pail does not account for temperature or the size of tip or the phase of the moon. My old partner told me paint should be the consistency of cream. Go ahead, tell that to the twenty year old, they have never seen cream.
My rep has nothing to do with the guy that helps me with my finishing. My rep was assigned to me when I got my account. The company's finishing guru is a guy that will come to my shop if I need help with a problem. I have his phone number and can call him when I have issues. He is very knowledgeable. I have called him twice. I figured everything else out by myself. I hate to say it, but it is not rocket science.
I use MLC products and the spec sheets tell you the basics.
It is pretty common basic knowledge that when it gets cooler, liquids will get thicker. That means you will have to put a little more thinner into the mix to get it to the working viscosity of the particular gun you have. You can put it in to the gun and do the test I described above and if you cannot get a good pattern by adjusting the gun, then it is likely you need to thin it out some more.
After you figure out what concoction you have to mix up to get a good pattern from your gun, you need to put the material on the project. Most finishes need to go on at about 3-5 mils wet thickness. To determine this you need a wet mil gauge. You can get that from your supplier or if they don't have it you can get it from Mohawk Finishing.
Spray your material on, just enough for it to flow out. This means that all the smaller droplets will start to join together and form a nice even sheet over the substrate. It really won't do that on the first coat nicely. But the second and subsequent coats will do it quite nicely.
Right after you apply the finish, you need to take the mil gauge and stick the appropriate edge into the wet finish and pull it out and touch the edge to a piece of paper or glass or wood. The thickness will be between the last wet area and the first dry area when you match up the gauge to the wet marks. If you are within your 3-5 mils then you are good. Thicker or thinner and you will need to adjust your technique. After a short while you will just be able to tell that it is the correct amount by the way it looks.
You mix your catalyst and finish up with the percentages that are required. Then you run it through your viscosity cup. Find out what the time is by using a stopwatch. If it is still too thick, then add a small percentage of thinner to it and measure again and again until you get the proper viscosity timing for your gun. If you don't have the correct cup, then either get the right one or find a conversion chart for it. There is probably one out there.
When you get to the right viscosity for your gun, fill it up using a medium or fine mesh cone filter. Then shoot it at the paper on the wall and adjust it until you get the correct pattern. Again, witchcraft, no numbers on the dial, just play with it until you get it right. Usually there is a line on the needle. Start with the needle all the way in so no fluid comes out and count out how many turns it takes to get to where you need it. Then use the line to record what time it is at, 3:00, 4:30 or whatever. Write it down or just remember.
Then spray it on your substrate and use the mil gauge as a test and then learn how to see the thickness. It will come to you with practice. This is assuming you are using an HVLP gravity style gun. If you are using a pump, things would probably be easier.
I use a mil gauge for one coating that really needs to go on about 2 mils thick and no more. Otherwise I try not to get it out until I need to troubleshoot. Obviously if finish pools or sags on a vertical surface, it is too thick. But just because something doesn't flow out doesn't mean it's too thin. You may have to retard the dry time, for example. Otherwise you may end up pushing the limits of wet film thickness in an attempt to get the whole mess to flow out.
To the formulator it's all chemistry. I suppose to a finisher the cooking analogy makes the most sense. You can't ignore the chemistry of the finish but it takes skill to get results that look and feel good. Having the right tools certainly helps and knowing some basic spray technique will get you started. You can mist away with all the atomized water or solvent you want, but until you waste some real finish nothing makes sense.
When I learned, I tried shooting sample after sample, and what that teaches you is how to spray a small sample. Everything changes when you go to spray a real project, and I didn't learn until I wasted a bunch of finish by messing up, and having to reshoot a real project a couple of times.
Spraying is also sort of like driving. You must be constantly aware and make constant changes to gun settings, or your technique. Drink too much coffee and you may be spraying too fast. I suppose color matching is about 10% color theory, and chemistry, and 90% skill, or perhaps some sort of evil magic if you want to describe it that way.
For anyone interested, I ran into a great solution for getting that perfect espresso stain finish. Call General Finishes and get a can of their water based espresso stain. One wipe on or spray coat, wipe, and you will be shocked how easy it is. No more multiple toner coats. Amazing product.
Especially here in the Bay Area, where the VOC restrictions change almost yearly, I don't know how the poor guy keeps up. Just when he has a good formula, has his techs trained to lay a perfect finish, he has to change to a new product and start all over.