The jury is still out on this one
Guys and gals are still trying to find the best method under paint
Lightweight latex spackle
Wood putty
Siliconized caulk
Crack shot
...and of course the massively expensive Azek adhesive caulk
Each method has it's own drawbacks
...spackle must be coated right away (ir it falls out)
...putty must be sanded (a sticky slope w/azek)
...adhesive caulk excesses is best "chipped off" with a hammer and putty knife (labor intensive)
If you are not coating them....well then why the heck is Kellstar doing anything to them?!?!
Lol
But really, if your not coating them, I'd suggest the Bond'n'Fill/AzekAdhesive caulk and chip method
I can't say I've tried it, but anything else I've done wouldn't work for Azek left uncoated, so I'd suggest that