Im just saying there is no need if you can do good finish work… on a 1.5, 1.8 or 2.0
1.0… yeah you are going to need something. But we have 2 guys who shape out of our place that can finish EPS to a near poly finish. without any additional sealing.
I prefer shaping PU but EPS is better for the environment and the locals here in the Philippines go through boards like crazy! Anyways, I appplied the joint compound to a small piece of EPS foam. It dried white but applying it just felt quite heavy. Not sure if it’ll work or not.
You can use the drywall sanding screens with the holders they are made for to sand EPS really smooth. A 220 screen will do it. Or just put it under a piece of soft foam. I save the foam they put inside of computer parts boxes for that. I use those screens to turn rails too. I’ve done EPS boards with and without the fill coat. I’ve done both the fast and final spackle (comes in a plastic bucket) and epoxy slurries. I really don’t know what is best, there’s pros and cons for either way. With a good surfboard EPS blank, you probably don’t need to spackle it. With the block insulation foam, you may need to fill the gaps.