I use green painters tape mostly. Paint flowing under the tape is usually a function of not burnishing it down to the surface enough or using to heavy/wet of a coat. When I spray masked markings I build up the color rally slowly in light coats.
One thing I’ve seen proposed is to seal the tape using the base color. Basically lay down the base coat, mask, then before spraying the masked color spray a very light coat of the base coat (clear coat also works). This seals the edge of the tape and prevents the marking color from bleeding through under the tape
“I was taught never just use the tape with edges as is. Cut the edges off as that is where all the dust and what nots collect making it less tacky then the other sections of the tape.”
FWIW: I have experimented and found that cutting the factory edge off of Tamiya Masking Tape does indeed leave sharper lines.
That’s why I keep my Tamiya in the little dispenser. The little bit that hangs out I use to tape the end back onto the dispenser and then I tear that little end bit off and have fresh clean tape to use. Unfortunately that doesn’t help with their wider than 4mm tapes.
You should wash models before painting. Smooth glossy plastic should be roughed a little, either alcohol, acetone ( which is strong ) or fine steel wool. Use a good primer. The stronger the better. I use Mr. Surfacer. I even use automotive primers for resin kits. Light layers with primers and paints. Careful of humidity. Allow good drying time, especially if going to handle a lot or perform masking. And yea, low tack masking tape with a short time left in place. The bleeding sounds like the paint coat was heavy. Also Vallejo is fragile and easy to chip and peel until a clear coat. Any water-base acrylic is, some more than others. You can use Tamiya’s lacquer thinner for a better bite onto surface. Hope that helps.
If I am reading this thread right, it sounds like you did not start with a primer coat. When shooting acrylics you must ALWAYS start with a primer coat. I use simple automotive primer and that works great for AFVs. For cars and aircraft, as others have suggested, Mr Surfacer might be better.
I was at one point very disapointed with myself for masking a recently painted (and fairly expensive) model too soon, and ripping the paint back of. I just was so eager to finish the model that I just could not wait…
At that point I decided no longer to use paints that don’t stick very well to the surface (basically I went back to good old Humbrol mainly)
I work on several models in parralel. That makes it a lot easier to just wait with one model while workign on another one.
Luckily, all my efforts to kill my stash have failed so there is always something interesting to grab
