Parking brake ineffective

[Eric Le Baron]

Replaced all brake discs and pads yesterday, all from ATE.
The discs were coated with greyish stuff.
First time I used the brakes they made a noise as if the pads were mounted with the metal part facing the disc!
After braking a few times the coating was gone (where the pad touches the disc).
As the same coating is on the inside of the rear discs I wonder what to do to remove it.
Right now the parking brake is not really effective anymore...
Should I use a similar procedure to wear off the coating on the inside of the rear brakes or should I have sanded the disc?