I originally planned to install new 12 x 12 self-sticking vinyl floor
tiles over the 50 year old 9 x 9 tiles in my bathroom. I thought I
could re-glue the few loose original tiles. Once I got started
pulling up the ones I KNEW were loose, I discovered almost all the
others were also loose enough to where they would easily pop up if I
ran a putty knife under their edges. So, wearing a 3M fabric face
mask and gloves, I easily took up all the tiles. What I have now is a
bare concrete floor with a thin, dry coating of old black mastic
firmly attached to it. I'm not wild about trying to scrape it off
because of the possiblilty that it contains asbestos. The mastic is
relatively smooth; it doesn't have the high ridges from notched
trowels like you see behind wall tiles.

What is the chance that the premium Cryntel Self-Adhering Vinyl Floor
Tiles I bought at Lowe's will satisfactorily stick if I lay them
directly on top of the old black mastic?

The Cryntel instruction sheet mentions priming concrete subfloors with
Latex Floor Primer. But it also recommends scraping subfloor first to
remove "materials that might prevent adhesion". Like I said, I'm not
wild about scraping the old mastic.

So, what should I do.....try applying the new tiles to the floor as is
(over the old black mastic), or buy some Latex Floor Primer to paint
over the black mastic?