I'd try to adjust the cylinder and blade gap first, as Ancient Geek said.
Backlapping - you will need to turn the cylinder backwards at a "slow" speed, 60 - 120 rpm. I used to apply the backlapping paste to the rotating cylinder with a cheap paint brush.
Remember to clean the stuff off when done, and adjust the cylinder gap. It shall be able to almost cut a piece of paper.
We normally used 120 grit paste, but 80 grit should be fine for your job.
I don't know where you are located, but PCPitchcaredotcom has the stuff.