Aegwyn11 said:
Can you help me understand why? I'm not sure I understand why the Rotex nullifies my work...the whole reason I was okay with spending $500 on a sander was that it is supposed to have the ability to be aggressive and gentle in one package. The Rotex seems to do the job just fine...not very aggressive at all at the low speed in RO mode. I understand that 220 grit might be a little low, I just haven't felt like buying more sandpaper just quite yet and thats the highest grit I have.
Sure I can help you understand why Nick. You know, the price of the Rotex doesn't mean anything in this case. Even if you take the most expensive sander of the world, which is your own hand, then it's possible to sand right through the fresh paint very easily. You have to realise, the layer of paint that's on the surface is very thin. When spraying cars in the family body shop, we generally applied a layer of 60 to 80 microns. Now if you paint wood with a brush or a roller, the layer is just marginally thicker, around 100 to 120 microns. 100 micron is 1/10th of a millimeter, or 1/254th of an inch. I mean, that's REALLY thin.
Now, no matter how good the Rotex is or not, that thin layer of paint is very fragile. Also because it isn't totally hardened yet. For fresh paint to harden out 100% can take 2 to 6 months, depending on the type of paint and the thickness. Putting the Rotex on that is like using a harvester to mow your lawn. You yourself said that once you get it smooth you're back to the primer again. It really is that easy to sand through fresh paint. Even by hand you have to be careful.
Another impression I get, is that you seem to think that the process of painting works just like the process of staining. The way you describe your approach to getting a good glossy finish is exactly the way I read here on the FOG how people stain their furniture and then do various sanding/polishing stages to work to a high gloss.
But that's completely wrong. Staining/finishing and painting are two different ball games. The stain is even thinner than paint and is designed to get sucked into the wood. This way the top layer of wood becomes permeated with the stain. When you start sanding it, you sand stain+wood at the same time. With paint, you don't do this. Paint doesn't permeate the wood. Or I'd better say, it's not supposed to. That's why you always have to apply a coat of primer first.
The primer is basically designed to do three things:
1 - Stop the suction of the wood. The thinner elements of the primer get sucked into the wood so that all the pores become completely saturated and won't suck any real paint in anymore.
2 - To fill out the wood grain. The thicker elements in the primer build a filling layer of material that lies ON the wood and even it out.
3 - To provide a layer with a good surface so that the real paint will attach securely.
Once you have a good layer of primer only then will you apply the real paint. The real paint doesn't even touch the wood. Just for fun, you should try out painting a small piece of wood with the real paint WITHOUT a layer of primer to see what the effect is. You'll see your paint get's sucked in to the point where it almost completely vanishes.
So let me recap, with staining you sand stain+wood. With paint though, you sand only the paint itself. Not the wood. Now as for the Rotex, it's more designed with the woodworker in mind (as all Festools) than the painter. It can assist you very well during the whole staining process, but not with painting because it's simply to strong and heavy for the fragile layer of paint. And that's not the fault of the Rotex. Almost any sander is. I never sand with a machine after the final layer of primer. Only by hand. And the only reason I sand at that point is to get rid of the last height differences and to roughen it up a little to get the best attachment for the final layer of paint.
Aegwyn11 said:
When the paint dries, it does have a high glossy shine. But it is not anywhere close to smooth.
Unfortunately, that's the nature of using a brush or a roller. It doesn't get no where near as smooth as a spray job.
Aegwyn11 said:
I figured that I should be able to get it smooth and bring it back to shiny through sanding/polishing...the problem I'm facing is that by the time its totally smooth, I've sanded through the paint in spots to get neighboring spots smooth. I've gotten better coverage with each coat, but its just taking forever.
When paint dries, it's not completely homogeneous. The heavier elements sink to the bottom and the lighter go to the surface. Now 'sinking' isn't the correct word because it doesn't rely on gravity but on molecular forces. But I hope you get my drift. The heavier pigments in the paint form the inner part of the layer and the lighter parts form the outer layer that gives the nice glossy shine. All you do when you start to sand that, is that you remove the shiny layer. All your sanding and polishing afterwards will not restore the shine as good as it originally was. Normal paint is not meant to be polished.
The best way to do this is to apply a layer of clear lacquer. On cars, we always used to do this. Without it the car wouldn't shine half as much as with it. We also sprayed furniture, and we also always finished with a clear lacquer. Polishing the layer of lacquer is perfectly possible. You can apply as much layers of lacquer as you want and polish it as much as you want. Just make sure you don't go through it and damage the paint underneath.
Reading this all back I think I could have worded it shorter, but hey, a little bit of background info is never bad I think. [cool]
Since I had the materials necessary, I decided to take 10 minutes and work one of the pieces up to 4000 grit to see what it would look like. And just as Alex and Brice said, it sucked. Pretty mediocre.
