Anybody who tells you to use Scotch-brite on deicing boots is nuts. Judging by this alone, the only thing your "knowledgeable" mechanic is knowledgeable about is blowing smoke. If you have Scotch-brited those boots, you have damaged them. Period. You will get holes in them in no time doing that.
First off, let me tell you how to do this job right. Get the PBS prep stuff and the PBS boot dressing. Follow directions, which are basically, for the Prep: wipe on, wipe off; for the Dressing: wipe on, wait a few, then wipe off excess. All done with SOFT CLOTHS. Job done in less than an hour for wing and horiz stab boots and NO DAMAGE TO THE BOOTS.
Second off, have a private talk with your mech...no witnesses. Tell him straight up that he can either:
a) do the job himself, his way, and absorb the cost, and keep his mouth shut or you're going to tell the boss that he's been doing to his $4M turboprop's boots what is basically the equivalent of sandpapering a condom prior to use; or, b) let you use the PBS as it was meant to be used (NOTE: the manufacturer of the stuff says twice a year is adequate) and keep his nose out of it, and his mouth shut. If the guy balks, just smile, nod, and use the PBS prep and dressing as I have described anyway.
Whatever happens, to cover yourself you need to let the boss know right now that this guys has been telling you to do something that is accelerating the wear and tear rate on that delicate neoprene by about 1000%. I have worked with a lot of guys like your "mech." When the holes start springing up in those boots he is going to tell your boss that you must have screwed something up, and you'll likely get fired. You must strike first and cover yourself.
But DO NOT Scotch-brite those boots!!!