Rolf,

Is it DIY foam or is it Epoxy foam ?

If it's the expanding DIY foam, that can dry as hard as nails (but the pressure washer might do it)

If it's poly foam than swearing at it might remove it <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Epoxy foam could be a major PITA !