part of the problem may be the product labeling
Vallejo Model Air "Gray Primer", # 71.097 is the COLOR gray primer, not an actual primer that is colored gray
for Acrylics primering to get paint to adhere to a model surface, and not peel up when masking or sanding, I just last week developed this way of working
I had tried the Vallejo Surface Primer # 74601 straight from the bottle, but, I was still getting lift off from the ship hull I was using as a paint test mule, even with Tamiya tape, Line-O-Tape, Frog tape and Blue 3M Masking tape
so, I searched convos around the model websites, and ran across the Craft Acrylics talk on here,,,,,,I sprayed and brush painted since that day I posted on here that I would be experimenting
here is what works
for brush priming, mix the Acrylic-Polyurethane 74601 with Golden GAC-200, in a 50-50 mix,,,,,let dry for 24 hours, mask with favorite low tack tape (even "shiny Scotch" cheap tape didn't peel pain in the tests)
for the airbrush, 2 parts 74601 primer, 2 parts GAC-200, and 1 part thinner (new Vallejo formula, Future, distilled water, etc), and 2 drops of Liquitex Flow Aid # 5620, again let dry overnight before masking
I used "part sizes" for the mixture to fill up a 1/2 Oz PolyScale bottle, so that I will get one bottle of ready to spray primer for each time I mix up a batch. I will be switching to the 1 Oz Floquil/PolyScale bottle with the next batch, though, I have a paint storage method that does not dry out paints, even though I am a "shaker" (shaking is not the problem, a good air seal+ no Oxygen in the bottle is the solution)