Woodworking is a lot of fun. And for many, it becomes a hobby that keeps expanding. Myself I have worked with metal as well as wood in order to achieve specific thing (repair the car, be able to fly radio controlled planes, ...). Then I bought a house, and did some home improvements, and a new house, and some more improvements. With my third house, it became different. We started to do not only repairs, but also some simpler constructions (spray painting wood curtain rods to make them look like metal, TV bench, work room table, cupboard, dining room bench, ...). If we find a ready built solution at good money, we prefer that.
But things like TV bench, cupboards, night stands and so on shall fit into the house and the room. Often, what is available is too big, too small, or deviates from what we would like to have. Building it ourselves, and painting it ourselves, has thus become a normal method. My wife paints well, but when high gloss paint became her choice, it turned out to be hard to do well with a brush. I am not a painting and finishing expert. I have just started to learn to spray paint, and get acceptable results. The initial tries and the route towards understanding how to do it where a bit testing, so I thought that I should summarise my findings to make it easier for others to get started.
The piece shown at the side is the first spray layer on a cupboard I had built. It is painted with Beckers Elegant V aqua high gloss. When the picture was taken it was still not fully dry. But the gloss can be seen already. Also, the reflections on the piece comes from the plastic "walls" of the spray booth and also shows a piece of paper that is used for testing spray gun settings.
The summary of how to get started with waterborne spray paint is simple:
- Get a good pressure feed paint gun and a compressor which can deliver enough air
- Aim for a good result, but understand that afterwards buffing paint is as essential as sanding saw marks in wood
- Get yourself a simple but adequate surrounding for painting
- Find a way to repeatedly set up your paint gun to similar results, although different settings per type of paint
- Learn to fix the most common problems, a failed first try is often salvageable
While younger I spray painted on my car, using aerosol paint cans, and my radio controlled plane, using an air brush. For wood work, I decided to spray paint with waterborne paints and finishes. The reason is simple, it saves me all risks of explosion from solvents while spray painting, and it makes it a lot easier to clean up after spray painting. There is even an additional advantage that waterborne paint does not tend to break up in distinguishable layers. However, it also adds a problem, waterborne paint is not always easy to use with a spray paint gun:
- Waterborne paints are thick, and thus more demanding when used with spray paint guns.
- Waterborne paints can often not be thinned as well as other paints.
The best solution is thus to use a pressure feed cup connected to the spray gun. In that way, you can get the paint to come on nice and even without having to thin it a lot. Also, as can be seen in the picture on the left, a pressure feed spray gun connecting to the pressure cup through a hose is quite small and easier to manouver than a spray gun with the cup mounted onto it, simply because there is no cup, only a hose, close to the gun itself..
For the gun you will need to have interchangeable needles, or guns with different sized needles, since different paints act differently. But with a pressure feed cup, you are not as dependent on the needle size as you would be with an ordinary paint gun (be it HVLP paint gun or not). For example, with my HVLP top feed gun, I need to thin a paint a lot in order to make it work with a 2.0 mm needle. Using a pressure cup, with the very same paint, it paints well without thinning, using both a 1.0, 1.2 and 1.5 mm needle (however I now thin the paint 5%). The paint I talk about is ordinary paint (Becker Elegant Aqua V 90 gloss). The pressure cup system would work even better using paint created for usage specifically with spray guns.
It is with painting/finishing wood as working with wood in other ways. It follows a similar pattern as so many other parts of woodworking. The tools matter, and the preparatory work matter, and in the end,some handtools are giving better results than only power tools:
- There is a difference between a truly high quality paint gun, and a low/medium price gun (the choice of tools is important)
- The more shine you want, the more of any scraches/dents/... in your material is revealed by your paint/finish
- The more shine you want, the more is revealed of any incosistencies in your applied finish
There is also a highlight: Even if you do not make a perfect job from the start to end, the end result can be saved and become good. Just like with other parts of woodworking, doing a high quality work all the way pays off. But as long as the work has been done good enough to be salvageable, corrections can be made. It is the quality of the end work (the finish) that finally decides the end appearance. And the end appearance can be redone.
The picture to the left is from my first try with the new spray gun and the unthinned Becker Elegant V aqua 90 gloss paint. This is the first layer of paint, just like with the cupboard on the first picture on this page. And the differences can be seen. This is not nearly as glossy as the cupboard. The paint has been layed on thinner. And look at all the scratch marks close to the light from the flash. All those scratch marks are made when sanding the board before painting it. They come from Festools orbit sander and P120 sandpaper. The board looked and felt smooth before spray painting it. But for a high gloss paint, P120 is a very rough paper. It is also possible to see some deep valleys, which are fish eyes, caused by me not cleaning the board with water before applying the paint, thus leaving some contamination which made the paint do fish eyes.
The picture to the left here is the very same door, with same unthinned paint, but after applying the second coat. The spray boot plastic walls are seen, and so is the reflection from them. The difference is big, there is now a much more even surface. The reflections show a very even surface. The scratch marks are gone. What differs is moving to a higher grade sandpaper (P240), and cleaning the surface with a wet cloth to get rid of a lot of residue before painting. The result is thus acceptable, and the piece has been saved. This can often be done. You want to avoid it, since it often involves a lot of manual work, but to achieve a good high end gloss, you will have to expect to do a buffing in the end, which takes care of some minor flaws.
I have read a lot about spray painting on internet. I have spray painted before, so I think I had a relatively good base to start from. Even then, it was hard to get a good view of how to succeed and to find good summaries of tips. Spray painting in itself, how to move the spray gun, is the thing available in many places.
So I did buy a couple of books on spray painting. That was a very good idea, specially one book that can be seen as a perfect starter book was filled with those small tips and advices that are so valuable to get started. The book was by Jeff Jewitt, called "Spray finishing made simple". A good thing with the book is a DVD which shows spray painting on video, and the fact that it is more basic and overview, than filled with information and details. This makes it easy to digest, and gives a lot of good "aha"s. However, that also means it leaves a lot of details out, so after getting started, there are other valuable sources to search in.
I had already made a lot of choices and was already painting when I bought the book. It immediately confirmed some parts I had already aimed for, and added a number of simple things on the "good start list", so below list is a summary form that one plus other sources:
- Make some kind of temporary spray booth. (Mine is simplest possible, two long plastic sheet "walls" mounted in the ceiling, reaching the floor, easy to get down and get up again.
- Assure a good exhaust fan. (Mine is a used kitchen fan, with a long aluminium channel which can be stuck out of a window)
- Place the material to paint on a turntable. (Mine is placed on a lazy susan, which in turn is on a cheap 4 wheel table).
- In order to be able to flip the painted material over, place it on a plate with a number of screws through it. (I started with painters pyramids, but simple screws through plywood leaves smaller marks and lets the material rest more stable on the screw tips).
- Use good lighting. (Mine additional light come from two cheap 500 watt construction lamps).
- Use a pressure cup. (This is essential. I have later in "The new wood finishing book" by Michael Dresdner found exactly the advices I have concluded on myself through experiments: with waterborne paint, go for smaller than expected needle sizes (he actually suggest 1.0 millimeter which was the first needle size I found good)).
- Filter the paint when pouring it into your pressure cup, which is done after mixing and stirring.
- Use a water filter on the air supply to keep the air clean through the gun (I use both a water separator, as well as an inline filter on the air just before the spray gun).
The above assures you have somewhere to be, which does not require a lot of space. It also assures spraying can be done without the paint bouncing back on you, the material and into the room. It also allows you to paint the material easily without trying to figure out how to reach all sides needed, as well as largely gets rid of particles and fish eyes coming from the spray equipment itself..
With all of the good advice from books, and with some experiments, I came to a set of conclusions on how I preferred to set up the gun. In many ways, it follows good advice, but in some ways, it also deviates from standard advice. It more targets the approach of returning to settings that works than to use standard settings or visible rules of thumb:
- First I select a needle. This is based on previous try with similar paint. I aim to use the largest needle that delivers a good result. So far, it might mean using the recommended needle, but more often I use a smaller needle than standard recommendation. I have never used larger needles than recommended since I moved to a pressure cup. What I have found is that due to waterborne paint viscosity, you have to go down to a needle small enough to assure you can atomise the paint. The normal advice aims at a needle large enough to get enough paint through the spray gun to paint quickly enough.
- Next I set up i the amount of paint that default (maximum) flows out from the paint gun. I want so much paint that on open surfaces I can paint easily and avoid sandpaper surface (happens if paint dries too fast) and so little paint flow that I can atomise the paint (avoiding orange peel). Also, I do not want more paint flow than I can avoid runs on vertical areas. To me, this means I want a minimum 1 deciliter paint per minute through the gun when no air pressurizes the paint. I measure it using 5 cl plastic cups readily available in stores for pouring liqour. I do not use any setting references of the kind "length or drop of flow" since I find that I want a similar amount of paint flow out of the gun independent of which needle size I use. It turns out I frequently end up around 13-17 PSI in the pressure cup, which is high compared to standard recommendations.
- After the paint flow is adjusted, I adjust the paint fan width to a suitable size for open surfaces (not more than 15 cm) and good atomization. The last need to be tested onto something. For that I use thick paper taped to a masonite board. It seems that a 35 PSI air pressure works well for the thick paint I use. With smaller needles, I can use less pressure. With more paint flow or wider fan, I need more pressure. Please note that I talk about pressure at the gun when air is flowing through (test by pressing the spray gun trigger to the point before paint starts flowing). It is a lot more pressure if measured at the paint gun when the gun is off (the 35 PSI when flowing corresponds to 55 PSI or so of statis pressure). The pressure is even higher at the hose before the pressure feed cup. The pressure difference is a lot more important for a high quality gun, than for a more normal gun. This since the high quality gun is needing a flow of so much more air through the gun that the pressure drops more, due to hose and connection limitations.
- If the test spraying shows incorrect fan shape, the settings need to be adjusted. If atomisation looks bad, I decrease flow of paint and/or fan width. Same thing if shape of fan indicates a thin middle. Also, when I lower the paint flow, or the fan width, I find I always want to adjust air pressure to a corresponding lower value. A moore in depth description of fine tuning the spray gun settings can be read here.
If you have good enough equipment, a resonable paint flow, a good atimization, and has read and practiced how to move the spray gun and on about what distance, you should now get fair results. But probably not perfect:
- The distance you hold your gun from the material affects the result. And depends on the paint flow you have set. The paint flow suggested above works well at distances around 15 cm from the material. But if you get too close, or move the gun to slowly, you will get runs.
- If you instead get to far away from the material with the gun, or move too fast, you will risk a sandpaper surface.
- A problem I had was that I had mixed the paint in a way similar to what can be done with a brush. But spray painting lays on a thinner layer, and the paint needs to be more clean. After stirring the paint, pour it into the pressure cup through a filter. Even better, have a filter between the paint and the gun as well. The last solved all paint particle problems I had, but caused problems with the flow. It highlights the importance of a very clean filtered paint.
If you have remaining problems, after this, they are likely to be:
- Dips in the paint (fish eyes). Comes from not having cleaned the material well enough before painting. Could be due to for example stearated sandpaper. Solution is to use wet cloth to clean the material before painting.
- Small sandpaper effects in the paint caused by overspray. Always start furthest away from the fan, going parallel to the fan with the gun, and for each turn getting closer to the fan. Doing that, the overspray will be mostly on the fan side, and be covered by wet paint in next turn. If that is not enough,move the gun slower or increase the paint flow.
- Scratches and dents and other marks. This is a woodworking problem if they come from what is beneath the paint. The surface need to be even. Prime it and sand it until it is even. Do not end sanding with coarser sandpaper than P180. Also, do sand after priming. One of the things the primer does is to make all problems easier to spot, so sanding and puttying after primer is to be expected. Do not sand before first paint coat finer then P240, because then the paint might not stick well enough onto the material.
- Uneven surface from dust or other particles. This, like the possible sandpaper overspray effects, is best taken away between every layer of paint, using sandpaper.
- Runs in the paint. Remove these with some kind of cutting tool before sanding (just like with woodworking, a plane can remove material evenly, sanding gives a nice surface but risk removing material unevenly). I like a Veritas horisontal plane. Normally, expect to put on a new coat after corrections like this.
- Expect to buff. If you do have more than just a little orange peel buffing might not be enough. Even without orange peel you might still have some small flaws in the surface. This can be expected until you have an extremely expensive spray booth setup. Think of buffing after spraying as natural as sanding after sawing. If you want a good surface, it needs to be done.