Depends if the coating is true heat cured, or it's UV cured.
Everything, every trace of silicone, oil, wax, carbon etc has to be removed.
UV usually uses xylene (a paint thinner) at minimum.
Some even use acid dipping to remove contaminants.
Surface texture is an issue with some coatings, blasting or chemical etching required to leave behind a surface the coating will stick to.
Then keep in mind you have to block, cover or coat the areas you don't want coated, without screwing up the ones you do want coated.
DuraCoat in particular is a little fussy about prep. I use a serious soak in something like xylene, then mask/plug the areas I don't want coated, then flush again with the DuraCoat brand cleaner.
If you want to do build-ups, leave those for last and use an airbrush.
It's hard to keep track of where this stuff is going once everything has a coat, airbrushes let you do that.
I suggest a bake and/or full cure time. It will skin over and leave soft spots underneath that will smear.
Just 'No Touch' until it dries FULLY.