Hi Fabio,
I use this for many things, when I'm filling a seam, I usually just apply it with a small brush, to the seam, Thinning it if needed with lacquer thinner. The times I have put it over any painted finish it has affected the paint finish due to the lacquer base.
If you use it on bare plastic to fill seams, you can easily take a cotton swab, DAMPENED with nail polish remover (the kind that contains acetone) and it will remove the excess, and you won't lose details by sanding. I use a real cheap brand from the dollar store, since the cheapy stuff seems to contain less acetone, than the top shelf brands, and is less harsh on the plastic.
If I'm going to use it to add a cast texture on an armour piece, I simple use a cheap, rather stiff brush, and brush a little on, and then stipple it, moving on a small section at a time.
If you find it is getting a little too thick in the bottle, simply add a little lacquer thinner and mix it up, like paint.
Before the introduction of Mr. Surfacer, back in the days of real teeth in my mouth, a full head of hair, and not needing coke bottle glasses, and when I winked at a pretty girl it was actually a wink, not an old man with a twitch, we simply used putty, and either liquid cement, or lacquer thinner. We just waited a lot longer for it to dry. We use to also desolved sprue in liquid cement (called it liquid plastic, or plastic padding... Gee, how original we were) and again we had to wait, and wait, and wait, some times we watched our models desolve in front of our eyes.
Another good use for Mr. Surfacer is in scultpting, you can simply build up your small details by painting several layers on top of each other, great for veins in hands, or resculpting fingers over streched sprue, (but that would be another topic) or really small features. Just build a few layers up, one on top of the other until you get the depth you are happy with.
I have hear of aircraft guys thinning it and airbrushing it on as a primer, but have never used it as a primer, other than along a seam. I sure the aircraft guys could explain that end better than I can.
Keep a window open, lacquer doesn't smell great and affects people in strange ways, and really isn't the healthiest thing to breath in too much.
Oh, don't go running out and buy Mr. Resin Primer, like I did, it appears to be nothing more than, Mr. Surfacer thinned down, smells like it, and acts like it, , but I personally still prefer Floquil Primer.
Hope that helps a little.
