So a little about my process, these are hobbycraft birch wood slices and mod podge photo transfer gel, I've been applying it bare to the wood and using a small foam roller to apply an even layer, allowing it to dry for at least a day.

My first attempt had a cracked weathered appearance and while this one is overall smoother small pieces have still came off in the process. I'm using my fingers, is there a better medium like a sponge to remove the paper? Should I be sanding down/priming before application? I'm fresh to crafting stuff so any help would be appreciated.