Dave,
Builders around central Minnesota have been using 3/4" thick wood veneered plywood (with a finished edge) to jamb out ICF and other wider wall dimensions. It is versatile because plywood is available in a variety of species and at a reasonable cost. Any cabinet shop could have this done for you- or I can send direct if a local source is not available.
From what I've seen and heard, it holds up fairly well.
Naturally, you won't find a completely water-proof jamb and you have to take care not to exposure to prolonged moisture. Even solid wood jambs provided by window companies will eventually rot and warp when wet. |