As far as thickness it depends on how it's applied and how bad the scoot shakes.I've seen 1/4" and more of mud sculpting out foward control mounts without a prob but i've seen the same amount bust out trying to fill a ST custom fender mount into the fender.You have to figure where the stress and vibration play into it and go from there.If I feel leary I'll weld in a filler plate to keep the mud thickness down.
