We are having almost no humidity here, 12 hrs dry time looking for light bond, did scuff one panel and not another and there does seem to be a slight difference. I am surprised though as it doesn't recommend scuffing smooth surfaces (although it always makes sense) and it says that is is good for plastics that are many times smooth. I guess that I was expecting a little more. Also what does everyone use for gluing hdu to an mdo backer?