Per Fasco Epoxies - they say if there is no sign of any delamination or bubbling, heavy sanding with 40 grit is enough to apply SS2k. If there is any sign of deep scratches, bubbles or delamination at all, the entire substrate must be sanded completely off prior to application. On this particular ski, there were no signs of any issues at all so I sanded deep with 40 grit, cleaned and applied. I offer a 3 year warranty against delamination on all of my work.