The dreaded and daunting hvlp. The most difficult part of spraying a finish is getting past the fear of actually trying. There is information overload out there (as well as bad info) that is enough to scare anyone away. Hopefully after reading this article you’ll have enough confidence to get out there and give it a try. Here is a link to the video explaining the basics of the process: Video, Read below for more info,
The spray gun:
We have already decided that trying is the hardest part right? Now that we are past that let’s talk abut what you actually need to get started spraying a finish. The first thing obviously is a spray gun, there is everything from the cheapo guns at harbor freight all the way up to the crazy expensive stuff. I would suggest to try and find a nice middle ground, Jay bought a pretty nice gravity feed spray for around 50 bucks. The guns from harbor freight are just too hit and miss for my liking. If you buy a decent gun now, you’ll thank yourself later.
Here is an example of a good entry level gun, cost around 50 bucks to purchase.
Here is an example of an acceptable air compressor size, at 20 gallons of air this thing can keep up with your spraying task.
The next item on the list is a compressor, most woodworkers already have one but you need to make sure that yours is adequate. The really small pancake style compressors just aren’t big enough tank wise or push enough cfm’s to realistically think we can use them for spraying. The smaller the compressor and the lesser cfm’s means the compressor will have a hard to keeping up with your spraying especially on larger projects. If you’ve already got a compressor around this size which most probably do, then you already have this covered.
Fluid tip sizes:
The next big hurdle is fluid tip size for the actual finish you are going to be spraying. Common sense is to be used here, the thicker the finish means the bigger the tip size your gonna need to spray it. Thinner finishes like shellac can be sprayed through as small as a 1.0 fluid tip. Lacquer, water, and thinned oil based finishes are more in the middle ground 1.5 fluid tip. For the thick stuff like acrylics (thinned), your gonna need a 2.0 or larger. You can obviously use larger tips to spray thinner finishes as well, but you have to be more careful because the larger tip will push more fluid and raise the likelihood of running your finish(which no one wants right?). The thinner finishes(milk paint,water based poly,lacquer, and shellac) are much easier to spray and are more recommended for the typical store bought spray gun. The thicker film finishes aren’t really recommended and most oils are actually easier to just wipe on. One way to measure the viscosity of your material is to use a stir stick. Simply dunk the stick into the material being used, then lift it out and count how long it takes for the steady stream of material coming off the end to break into dripping. For paint, 20 to 25 seconds is where you want to be, and for oil base varnishes, 15 to 20 seconds.
The gun setup:
There are three basic controls on a spray gun, the fan pattern, the fluid control, and air regulator(some guns have these built-in). The fan pattern is actually quite easy to dial in, the way I recommend is to dial it all the way in to the smallest fan pattern and slowly adjust out until you get a full and consistent spray pattern( I test on a scrap piece of paper or wood). The smaller you set the fan pattern the harder it will be to be consistent and more likely it will be to run. The fluid I usually keep dialed all the way out, the way to adjust is turn the knob all way out and then dial it back in until it starts pushing the trigger forward(you need to be pulling the trigger while doing this). Once you feel it pushing the trigger forward you know the fluid is at it’s largest capacity because it’s at the full extent of the trigger pull. It’s easier to just keep the fluid adjusted out and limit the amount you apply by the speed of which you apply the finish.
This is an example of a properly tuned fan pattern. You see it’s nice and consistent top to bottom.
The air pressure is the last and probably most daunting aspect of spraying. The suggested air pressure that comes with most guns is just that a suggestion. It’s based on the fact that you have the perfect setup, compressor size, air line size and length, and proper air regulator, which most weekend woodworking shops don’t have. You only need enough air pressure to properly atomize(which means break the paint into small particles) the finish your spraying. I don’t like to rely on the regulator in most cases unless of course you own a high end one. What I suggest is the start out by dialing the pressure all the way down and slowly add more pressure until you can see that it’s properly spraying the finish, you can tell because the finish will spray nice out of the gun and not splattery looking. That’s all the pressure you need for that finish, once you establish what that is, you can use that for future reference with that particular finish.
Applying the finish:
Make sure to always start and stop your pattern past the edges of your project to prevent puddling.
The application is the part that takes the most time to get good at, practice is the only way to learn how to properly apply a finish. The simple things are keep the spray pattern 90 degrees to what your spraying and keep your speed and distance(about 10 inches from the surface) consistent. I like to start by spraying the edges first and then the face of the boards next, making sure you are overlapping by about 50 percent on each pass. You want a nice consistent thin film build over the entire project, not too wet and not too dry. Puddles and runs will make the finishing process much harder as you will actually have to sand out these problems before applying another layer of finish.
This is the part that most folks neglect when spraying a finish on. You must keep your gun clean in between jobs to keep it spraying properly and working the way you want it to. Flushing the gun with some solvents after spraying will help aid in this process. You will also want to take the gun apart and soak the parts in solvent overnight to ensure everything gets properly cleaned. A little gun lube when putting it back together will keep all the parts working properly.
I hope i have simplified this process for you because that’s really what it is, simple. Once you get used to spraying finishes you’ll never wanna go back to brushing them on. The speed and ease of which you can apply a finish by spraying is really unmatched. All it takes is a little time and practice and you too will be able to achieve nice sprayed on results, so get out there and give it a try, you’ll thank me later 😉