going to seem a bit of daft question, but I have bought some new ebc red stuff pads and really having trouble getting putting them in without them clamping the disc

pistons have been pushed back using the backing plate of the old pad and piston compression tool to ensure good contact on all pistons, it seems to be the breaking in coating on the top of the pad that is making it too thick

how quickly does this stuff come off or anyone got any advice if you have fitted these before in standard callipers