Originally Posted by Kennay
I don't think there is anything wrong with the US foam. I think some people aren't competent enough to mix it correctly. For proof, just find the people complaining, and look at their builds.
No offense to them.
I have not used the US stuff, but I'm about to order some. I know the stuff I have (Tap Plastics), you need to mix very well for a very thorough mixture. I also heat the garage up to 80* when it's really cold, other wise, just preheat the hole I'm pouring the foam, preheat each part of the foam to 80*, then when I pour it, I use a heat gun and heat the foam while it's expanding.
And ya, I stay way from foam in a can. That stuff requires air to dry, so it's really bad to use behind foot holds or anything. Also it takes forever to actually harden enough to sand and form. 2 part stuff reacts and hardens by chemical reaction.
I use 2lb foam for everything. You will find if you are using it as a form, it will have some air pockets you might have to fill when using it before glassing over. It's not quite as strong as 4lb which some one here will recommend. So for under the tray, you will want to make sure the tray glass itself is strong enough to support you without relying on the foam for support. The 2lb does add some support though. As a bonus, with the 2lb foam, you are basically getting double the quantity of foam for the same price as the 4lb.