Overspray finish inside cabinets
What's the best way to prevent it? June 24, 2002
Q.
I am not getting as smooth a finish as I would like. I am spraying 1 coat vinyl sealer, 2 coats cab-acrylic (all SW brand) and using a Binks pressure pot with 2001 gun with the recommended tip set up for this material. Also, I am not reducing anything and using about 8 lbs of fluid and 30 lbs of air.
The main problem is with overspray, especially the inside corners of cabinets. Should I be rubbing the finish out?
I know, I should be using CV!
Forum Responses
From contributor S:
Don't even think about it. Rubbing is an endless path and rubbing inside a cabinet a dead end. I only rub when I want full gloss and this is polishing, not rubbing. Also, if possible, take the backs off of the cabinets and reattach them after finishing. This makes everything a thousand percent easier. The key is to slow down the flash of your lacquer. This is one of the reasons that you should be using C-V, as it has a much slower flash off, but since you already know that, I won't beat you up about it. I use MAK (methyl-amyl-ketone) in my lacquers all the time. I live in Phoenix, AZ, so I must do this to get any flow out.
Here's the plan - do all of your sealing and your initial topcoating as you did before. Sand everything nice and smooth. Now it's time for the money coat. Use about 6 oz of MAK per gallon of CAB and shoot a nice wet coat of this. Stand back and watch the flow. Let it dry and ship it.
I agree with the above post, with one exception. If for whatever reason you cannot do the back panels separately, reduce your sealer as well. As a rule, I ask that the back panels not be attached prior to spraying anything. I want to be able to breathe, with or without a mask.
From contributor D:
Isn't 8 pounds of fluid pressure too much? Here's one way to tell: turn off the atomizing air and press the trigger to the gun. Let the stream of fluid shoot out of the gun nozzle. How far does it shoot before the arc is vertical? Unless I am off base, I think this arc should be 15" to 18". That's how you can tell if you have dialed in the correct fluid pressure on a pressure feed gun.
From contributor W:
Here in the high desert of New Mexico, we add 5 oz. Butyl Cellosolve per gallon of CAB Acrylic the moment we pop the lid; it's about 4 times slower than MAK, with a longer flow-out time. Any reduction we feel is necessary we do after that. Butyl Cellosolve is available at SW, but it's not HAPS compliant.
But the best answer is to keep the backs off the boxes until you finish them (or use pre-finished NovaPly if the client wants a veneered box).
I agree - 8 lbs material pressure is high for shooting this material. I think checking viscosity is a must when using a pressure pot. Unless your material is a consistent viscosity, you will struggle to find the proper material and air pressure settings. I find it much easier to control the viscosity first, then my pressure settings stay generally consistent. (4-6 lbs material pressure, 30-35 lbs air pressure)
I measure every batch of lacquer after I reduce it with a #2 zahn cup. I shoot for a measurement between 19 and 20 seconds. The amount of thinner needed to reduce will vary with atmospheric conditions. I live in Kansas, where changing weather is the norm. Sometimes I will need over 2 gallons to reduce a 5 of lacquer. The next week, it may only take a gallon and a half.
Sometimes I question what my material gauge reads at the pot, since it isn't very sensitive to fine air adjustment. The visual check I use along the line of the one contributor D suggested is to look closely at the fluid stream coming out of the tip (without the cap, of course). I look at the distance from the tip to where the solid stream begins to break up. When I am getting good results, that distance is about an inch, maybe a little more. Check this often and eventually your eyeball gauge becomes pretty reliable.
I agree with removing backs whenever possible to reduce the overspray problem, but if the backs are on, I usually reduce my air pressure quite a bit to cut the overspray down. This can result in orange peel, but usually the viewing angle inside a cabinet would make the orange peel very hard to see.
If I still have some overspray inside cabinets after the final, I just rub next day with 0000 steel wool, dry. Just a quickie rub - nothing aggressive. If you have more overspray than what that will take care of, you need to correct the problem in application.
From contributor S:
Contributor W, I don't like the Butyl Cellosolve answer to the flow out question due to the nature of glycol ethers. They are plasticizers and become part of the dried finish. They never really flash off. In my experience, the finish never (even after years) reaches its normal hardness. The way that I noticed this is with things I would build that I stored heavy objects on. I built a record album storage cabinet once using a butyl cellosolve reduced lacquer finish, as you describe. It was a month between the time that I finished it and when I put it into use. The weight of the albums distorted the finish. Even now the finish is flexible, rather than hard. That's why I like the MAK. It stays around long enough to get the job done but doesn't wear out its welcome. It knows when to leave and doesn't incorporate itself into the dried film.
If it's just the overspray that's your problem, ball up a brown paper lunch bag and rub the overspray off. Easy, clean and fast. Don't do this to high gloss, any black or white. The trick is to keep rewrapping and replacing the paper. If it clogs up, you will see some scratch marks. This is an old trick that a Guardsman rep showed me years ago. It works great!
From the original questioner:
I think my technique is fair. It sounds like I need to get a Zahn cup and start keeping up with the viscosity a little better so I can get a handle on the air pressure. Also, I guess I should be adding retarder. I live in SW Georgia where it gets hot and humid. By the way, I do spray with the backs off.
Now if I can just learn to get rid of those hot spots at the rail and stile intersections.
I use the same finishing materials you use but never have any problems - main reason? Flat finishing all components before assembly. I am frameless so you probably would need to finish your ff's after assembly. I only finish one side of most cab parts, as I use applied ends. Most of my work is melamine, but I do a fair amount of veneer panels.
One thing I have learned recently about my finishing techniques is that I was not sanding thoroughly enough between coats. I now sand very carefully (320) after one coat of vinyl sealer and two finish coats, tacking and/or blowing off after sanding and putting on full coats. The finish is spectacular - even and velvety smooth. I use med. rubbed effect.
I thin about 25% and don't use a Zahn cup, although I think I will begin to do that just to keep things more scientific. Vegas desert makes finishing easy - no moisture problems, etc.
Mohawk makes an aerosol product called No-Blush. It works great inside boxes. After spraying your wet coat just mist a little No-blush in those areas where the overspray builds up. As to those stile and rail hotspots, just use the air assisted airless technique and spray everything in one direction. If you spray with the grain on the stiles, go across grain on the rails. That way you don't get 2 coats where the pattern crosses.
