Does anyone have experience with using Trex for window bucks? Since Trex contains plastic, is there a problem with too much expansion? Will Trex have to be braced more so than wood? Will Trex hold paint well? Any problems with using Trex for window bucks?

I'm just going on a guess here, I don't think I would entertain the idea of Trex for window bucks based on what I have seen it do for decks with expansion and contraction, even though it is exposed to the elements on a deck I would think similar results especially on a south facing facade. I can also see additional bracing being needed to secure the forms and keep them straight during the pour. And when it comes to securing the windows, I see an issue with fastener bonding into the plastic, expansion/contraction issues again.

Why would you be considering this product for such a use?

Need a low maintenance, long lasting door/window buck for a Structural Concrete Insulated Panel (SCIP) wall. Trying to avoid treated wood bucks. What other material should be considered? Any problems with using fiberglass angles or channels for bucks? I just found this article that may be helpful if I can devise some way to use ICF bucks with SCIPs. http://www.icfmag.com/articles/features/window_bucks.html

Ive seen Trex used in an 11 story Drury Inn in Tn and they regretted putting trex in due to expansion. It was wavy and the attachment wasnt that great in my opinion.