Turn hand painted dirt Base Color layer to Roughness

I would like to make the dirt layer I painted on, effect roughness. Though im not to sure how to isolate the the alpha. Like I want to effect just the dirt roughness not everything. The normal seems to work pretty good just plugged straight into height, such as what was done with the long-board….. I THINK I GOT IT! Run the texture layer through a Color Ramp with one pole having 0 alpha. Could maybe be better refined with control but im happy with it. Slowly becoming more node competent :p. Could of maybe painted on as linear black/white map(roughness perchance?) and ran through color mix rgb to give it 2 color blends