When the last layer of spray paint has been applied, it is time to secure the final finish. From the preparation for the first layer of primer until the last coat of paint, everything done has been done to assure a good final finish.
Many times when looking at the paint result of a commercial piece, and comparing to the paint result of a home made spray job, there is a huge difference. The major part of that difference come from treating the paint differently than other tasks in the process of woodworking. After the paint is put on, the job has to be started to give it the desired finish. The final finish is achieved through polishing the paint. This is to be seen in the same way as sanding is done to give the assembled wood pieces a better surface.
After the last coat has been applied, first step is unfortunately to wait. For waterborne paint, the waiting is about patience. The target is a dry and hard paint. The paint must be dry enough and hard enough to be possible to polish to gloss (the amount of gloss is adjusted through how the polishing is done):
- If the last layer is thin, and without runs, a couple of days can be enough, but then polishing paint has to be done very carefully so the paint layer is not destroyed.
- If there are runs to remove, waiting has to be longer.
- If the polishing is aiming for high gloss through polishing, ideal is to wait around three weeks for waterborne paint to dry thoroughly.
When the paint has dried enpough, first thing to do, just like between layers of paint, is to make the surface even. However, now it is to be done with as little scratches as possible, since next step is polishing to gloss. To remove small particles sticking up in the paint, use sand paper. As before:
- Use the finest sandpaper that is coarse enough to remove the unwanted particles
- Use a hard backing behind the sandpaper.
Possibly, 2000 grit, us standard, is coarse enough. Coarser then P1000 european standard is best to avoid.
If there is a lot of paint, orange peel can be removed with coarser grits than so, but since it will take a couple of grit sizes from that to remove the scratches, there need to be enough paint left for that sanding work.
Polishing waterborne spray paint is started first when the paint surface is plane. If needed, rubbing is to be used. The longer the paint has dried, the harder it is, and the heavier rubbing is needed. I have found that:
- From sanding with 2000 grit american standard, Festool MPA 6000 rubbing is quite suitable on a paint dried for three weeks.
- It will take some time to remove the scratches with that rubbing (using a medium sponge).
- If the paint has not dried so much, MPA 8000 and a fine sponge might work.
- As for sandpaper, the target is to to polish paint, use the finest polish that is coarse enough to do the job quick enough..