a lot can be said on this subject and not enough also. I never mentioned my procedures simply because it's a topic that many covers many variations and preferences. Personally I prefer Lacquers and HVLP method of spraying. Years ago most shops sprayed conventional with the use of booths and well ventilated surroundings to handle the tremendous build up of spray mist. A draw fan was a must, and in most cases a commercial type so as to suck out the fumes, and keep up with production. For the hobbyist and part time user, this was a major problem area. Not only for the health hazard, but also the danger of flash fire. I can remember the fumes being so thick, I couldn't see across the room, and breathing in the fumes had me so high I couldn't feel my feet touching the ground. I'd have to walk out of the shop and leave the window fans clean the air for 10 min, before resuming.
HVLP was a God send. It replaced the conventional system and eliminated the fume build up in the air, let alone spray dust all over the shop afterwards. The big thing that I found nice was the amount of finish being saved because it wasn't going into the air. Not only was it not going in the air, but also not in my lungs as well. This means, more finish on the project, so less coating, saving both time and money. It took a while to settle on a good system however, as not to many people were anxious to change over. There was a lot of talk about HVLP, but to find actual users for the experience and feed back, was like looking for a needle in the proverbial haystack. I got my feet wet on a low cost unit with its own turbine. The finish was decent, but nothing like my conventional finishes I was accustomed to. Eventhough it wasn't, it was worth staying with simply for health reasons, and the fact I saved almost half the material I normally used, which meant big savings. The pro set ups were pricy and not to many wanted to experiment, and I was included in the lot. Many companies converted to conventional set ups to aid in the big expense switching over, but for the most part it didn't catch on to well. Conversion guns were an introduction to HVLP, and some did rather well with them, and still use them, but many who had the conversions, switched to the big boy's and true HVLP guns such as the Mack 1 S-1, by Binks (the one I have). It comes with either a cup, or pressure pot for consistent dripless spraying and ease of getting into tight spots. I used the Binks 2000 series conventional, and Devil Bliss prior to HVLP, and Binks delivered the best finish and still does with the Mac 1.
The reality of it all is, while we invest a whole bunch of money on woodworking equipment, we always tend to be leery doing the same on the spray end. We don't balk to spend 1000.00 on a cabinet saw, and yet, we look for the 100.00 spray gun?To find out more on the Binks you can check them out at: http://www.binks.com/
Now...... the purpose of spraying is to achieve the best possible finish one can get, with the least amount of labor. By this I mean...... with the standard hand applied finishes, it requires several coats and layering to get that luxurious deep finish. This means many hours in drying times, and of course sanding in between and hope and pray a fly doesn't kick up dust on your work while drying. The other thing is, if you have more than one project going on and finishing with an oil based product such as a varnish, or urethane can tie up your shop for several days. I like lacquer simply because I can be completely done with the finish in one day, regardless of the size. There are a few things to worry about, but in most cases it can be corrected and controlled, as opposed to dust.
Runs for example...... they occur generally when the material is to thin. Simply add more solids and spray again. I always have a test piece that I spray first to see how my pattern is, and how wet the material is laying down. If its to wet, runs will develop. Having the right mixture at this point can be adjusted by one of the control knobs on the gun. For this, a test piece is the best way to determine what you'll need. Spray a 2 line pattern, holding your gun about 10" away so you have a good area to view your work. The fist coat of sealer won't tell you a whole lot because of the grain raising. Sand and re spray, not let this one dry. Look at it at an angle and this will tell you if you have sag or running. If neither, once dry feel the finish. If its dry (rough) then your material starved, and adjustments for material flow is needed or material needs to be thinned, and now is the time to make adjustments. Don't run through this important step. Spraying needs practice, and many trial periods will be needed. For a test piece, I like at least a 30" wide x 4" high. This way I can see my pattern, and overlaps. Once you find that right mix, it will become almost second nature the next time you spray. It takes about 5-6 projects sprayed before you will really build a good familiarization in spraying.
Now comes the compressors. Some will say you need these gigantic monsters and professional this and that, and the truth is that you can spray with a pancake compressor. I've done it! Now here's where the problem comes. A small compressor will run more frequently because of its air storage capacity. Although the HVLP uses less air, it doesn't take long that if one were using a small pancake, it would kick on, and probably stay running. If you were spraying a table top, then you'd have to let the air build up before you took a chance to spray that large area. I also sprayed with a 10 gal compressor, but it also ran quite a lot as well. Now the more a compressor runs, the more moisture it produces and sooner or later it will travel the hose, and spit out on to the work. To fight this, a set of bottles can be placed in the line to catch the moisture before it hits the gun. This should be emptied frequently, during a spraying operation with a smaller compressor. For all intentional spraying purposes, I recommend using a 5hp 20 gal compressor as a minimum. I recently increased mine to a 60 gal, due to the fact I picked up a good price on an upright which takes up less shop space, for my needs. No mater whether you use a 5 gal, or a 60 gallon.... the quality of the finish will be the same. The only thing that will affect it is moisture spits, and running out of air doing a large area.
Setting the gauges and the right mix (pressures and material flow) can be a bit frustrating. Even someone with experience will have to play with adjustments, but once the right setting is achieved, then it doesn't require any more from then on. Also, different tips are required to shoot different materials. For cabinet lacquer I use 94P tip, and for oil or water base paints a different tip will be needed due to the different material to flow and lay properly.
I found that the best setting so far for me was 20 lbs on the compressor going to my pot
and my pot pressure to be about 6lbs, and out the gun with the trigger depressed I have 20 lbs and when not depressed its right about 30 lbs.
And now started to experiment with the material flow and pattern. Thinning, and re testing on a sample piece and when I was done, the gauges stay put from here on out. When spraying a pigmented lacquer such as white..... the settings do change slightly.The Best method I found at setting is to shut down the air flow to the gun. Set the compressor pressure to 20lbs., and adjust the pot so that your left with6 lbs. When squeezing the trigger, you should be shooting a small steam about 4' out. Now open the air on the gun till a fine wet mist is achieved. The fan should be about 8" to 10" about 8" away from the subject. Its wise to have a large sheet of 1/4" dark stained plywood. I use birch due to not having large grain cavities as oak will, so you can see the evenness of the applied finish better at an angle. I like to leave the plywood leaning up also. This will tell me if I'm to thin and will run on my project later. When the test piece is dry and feels sandy, then more thinning is needed
In the actual finishes, there is a general misconception in that, one just goes buy 1 gallon and start shooting. Wrong! Any lacquer needs a sealer, and special sealers are made that are soft and easy to sand. There are two basic sealers. A sanding sealer, and vinyl sealer and both are easy sanding. This makes leveling of grain surfaces easier, as well as a good build needed for that soft and deep finish. The sanding sealer is sanded with 320 between coatings, and I prefer a 1/4 sheet finishing sander for this. The reasons are, that the square pads get into corners better than the round sanders, and the paper is cheaper in sheet form. From one sheet, 4 pieces can be utilized. I generally put on 3 coats of sanding sealer, depending on how I like the results after the third. One satisfied, I apply 1 or 2 coats of top coat, which is usually a semi gloss Acrylic. The acrylic is more expensive, but it's a harder finish than a standard lacquer. Not to be confused with auto acrylic and its reputation on hardness. Cabinet lacquer acrylics are specially formulated. The auto acrylics are not flexible enough for wood, and will crack.
Depending on the humidity and spraying conditions, retarder may have to be added to the material to avoid blush. Blush is a cloudy affect in spots as part of the finish, and will often turn white. It usually starts to show up on the 3rd coat of the sealer, and for sure on the top coat. Blush is the air moisture, or humidity in the air that becomes trapped under the fast drying lacquer and the reaction becomes a cloudy affect. A slight sanding will open the last coat of finish and allow the moisture to dry, or leave and the next coat with retarder will soften that previous coat and avoid future blush. Retarder is just what it is. Its an agent used to slow down the drying process of the finish. The use of this is minimal and also has to be experimented with according to the relative humidity in your area. Most shelf lacquers are considered "Hot". Meaning that they dry allot faster than bulk lacquers found at paint suppliers. Most of these are sold in 5 gal. lots, and usually are slow drying lacquers.
When I lived in New England, I hardly ever used retarder, but since moving here in Ga., retarder is an every time use from the 3rd coat on, and especially in the final coating. I buy my finishes in 5 gal. lots. A normal kitchen takes 3-4 gal of sanding sealer, and 1 ½ -2 gal of top coat. If I do have to buy in 1 gal containers for small projects I use a pouring lid, because pouring from a gal can me quite messy.
I'm often asked what I use to rub out my finishes, and I must admit I was a bit confused the first time I head this. I never rub out a finish! I attribute this to a good spray set up, and the manor in which I spray. To spray, and have to rub out after is time consuming, and not cost affective. That's not saying you can't rub out a lacquer finish for better feel or look. Lacquer finishes can be rubbed with fine sandpaper, steel wool, or rubbing compounds. The only area that may need attention might be the inside corners (over spray) and in most cases, a quick pass with #0000 steel wool, will cure that. There again is another area that kind of comes with practice. Over spray inside, due to the slow leaving mist in a confined are will almost always produce an over spray, even in its minor appearance. Over spray also comes from finish bouncing off a wet area, to a dry area. A way to solve this is to keep the entire inside wet by adding more retarder to the finish. The floating spray will eventually fall onto the wet area, and re-dissolve into the finish. Adding more retarder also aids against orange peel as well, as it gives the finish time to level out before setting up.
Make sure when setting up an area for spraying, that you have a good means to remove fumes. I use a commercial exhaust fan.
It Never fails, everytime I get ready to spray? The sky's open up, and it pours. Better get the retarder ready
I took a chance in spraying today, knowing it would be a futile attempt. One thing against me was the fact I use an exhaust fan to remove the fumes, and I crack the overhead door about 1" to create a current. Naturally when this happens, I let in humidity, and if its real bad, then it just makes it all that much harder. I did however, want to show some of the troubles that can occur, and how to combat them. On days like today, you can absolutely count on blush to appear. Blush are those whitish area's you see on the face frame
and again here on the side panel. I remember the first time I ran into this I wanted to cry. This occurs when there is to much moisture in the air, and it gets trapped between the lacquer and the lacquer dries leaving it there. Two ways of fixing this. Shoot straight lacquer thinner over it several times till the moisture leaves it, or wait till it dries, sand, and shoot again but this time add retarder to your finish. How much will depend on the humidity.
Retarder comes in gallons most of the time, and a gallon goes a long ways. Chances are you'll through out the remainder at the end of the year. Shelf life depends. I've not seen retarder last longer than 1 1/2yrs. at best.The thing to bear in mind on retarder is that it slows the drying process down, so naturally it will take longer to finish a project. It also thins somewhat, so you have to test a piece for running
Another trouble maker are runs. Runs happen for a number of reasons. Spraying to close to the object. Staying in one spot to long, material to thin, humidity causing sag, or someone upstairs is paying you back for something you did, and so on.
Several methods one can use and this one my dad (retired auto body man) showed me . Have some masking tape handy, and while the finish is wet, take a strip and gently glide it onto the run and let the tape rest on it, then pull it off. This will take the run out, but it still has to be sanded and shot again.
If a run dries, sanding it will cause material removal in all areas, an chances of bare spots or lighter areas surrounding the run are pretty good. A good clean sharp cabinet scraper comes in nice right about now, just to take the run itself off (the high spots) Care must be used, as the finish may be dry to touch, but still is soft. With the run itself gone, wait ten minutes or so, then lightly sand, and spray another coat
I use a sanding sealer. There are many different sealers, including a vinyl. Here I'm using a plain sealer. I sand between coats with 320 wet and dry paper. The first sanding, I do by hand, just passing quickly and feeling with my other hand as I go. The purpose of this first sanding is to remove any whiskers and dust. Whiskers is the name given to wood fibers that raise when wet, then dries causing a dusty or rough surface. Remember the first coat is just a light coat, and to do this with a sander at this stage, you run the risk of bare spots, especially along edges.
Now.... let me clear up the misconception on sanding sealers. Yes, it is a softer finish. The reason is due to the simple fact of building, and leveling the surface. Sanding, especially on the second or third coat starts the leveling process meaning that when your sanding, you are taking off the high spots of the finish and not allowing it to continue to build. This allows the open grain to gradually become even with the rest of the surface. If this is done right, then once the 1 or 2 separate final coats of a "top coat" finish is applied, it will be just as durable as a finish without sealer except .... the finish will be more luxurious and deeper in appearance, than without. Most production type finishes do not use the sealers, because its just another step and more material used and carried for inventory. But all you have to do is try it both ways and see the difference. Note in the pic below, the white sanding powder fills the grain pores. An indication that the grain still is lower than the rest of the surface.
Once the second coat is applied, now I'll use my 1/4 sheet finishing sander. I like the finishing sander for this because it gets into corners a whole lot better and easier. Its also nice when sanding the stiles. Note how I place the sander on the stile. This angle prevents bumping into the joints, as well as minimize possible bare spots on the edges. Now.... sanding should be quick passes, and light. Just enough to powder up, and sanding sealer is designed to do just that. Powder up easily for a building process
here's a good shot of how powdery sanding sealer gets when cured and sanded properly with 320 wet and dry paper
If your paper looks like this when your sanding, either the finish hasn't properly dried yet, or the stain hasn't cured right before applying the finish. Best to wait a while longer before continuing
As you can see, the blush and runs are gone, and now the 3rd coat of sealer is laid down. Judging how it may look when it dries, I may leave this one, or spray one more. Note that I do use a mask, and also notice that the HVLP system, hardly sends off mist compared to conventional spraying. My gun here is held 6" to 8". I overlap my fan, making sure that the entire area is wet. I spray from the top down, and left to right, taking my finger off the trigger at the end, then depress the trigger and spray the next line from left to right and again releasing the trigger at the end. This method saves material, but also develops a habit that will aid in control as you spray face frames and not getting a build over joining pieces, producing runs
For the drawers, I like to use a step ladder. I spray the inside first with the bottom side, the two sides, then I flip the drawer around and do the remaining end and top edges. Then I spray the long outer sides and one back. The end that will be against the drawer front, I don't spray
this is that same cabinet above that had all the blush, with 3 coats of sanding sealer. I think I'll do one more, then a top coat of acrylic semi gloss
A good tip for you. Find a small paint center and check out to see if they have toners. Toners are a tinted lacquer great for blending or touching up accidental bare spots from sanding, then shoot a top coat. Can pull you out of a serious jam at times. You can often find these toners to be the perfect shade to the stain colors being used. Great for blending lighter areas to have more uniformity
I will add to this as I continue with the spraying of this project