FIRST of all - its P-TEX, not T-PEX.
second, the board should be unwaxed, and clean. either clean it with a base cleaner or go over the whole base with your waxing iron following the old melted wax with a paper towel to remove it.
if you waxed and then Ptexed you'd be dripping Ptex on top of wax. you want it to bond to the base.
watch youtube vids on how to do it, make sure you keep the stick super close to the base so it doesn't flame yellow.
only ptex stuff that hits the core or comes real close to it.