Q. Can concrete form boards be reused for framing, or does exposure to concrete weaken framing lumber?
A. Bill Palmer, president of Complete Construction Consultants in Lyons, Colo., responds: It’s best not to use forming lumber and plywood for anything but forming. Even though the IRC doesn’t prohibit it, reusing form boards for other purposes — except perhaps in noncritical locations, such as for blocking — isn’t a good idea. Many of the reactions that degrade lumber naturally occur more quickly when it’s exposed to concrete. Adding to the problem, many of today’s concrete mixes have a very high pH and alkalinity that will burn off the surface layer of any wood they are poured against.
Simply cleaning the lumber isn’t a reliable solution, either, because you may not remove enough of these corrosive chemicals to prevent long-term deterioration — and the act of stripping the wood form may cause damage that isn’t apparent until the wood is put under load. For example, if 2x12s used to form a slab are later used in load situations that require 100 percent strength (such as in window or door headers), a 25 percent strength reduction caused by chemicals in the concrete or by stripping damage could result in a very costly repair — or life-threatening failure. Don’t forget that forming lumber is expected to last 30 to 90 days, while structural lumber is expected to last 30 to 90 years.
Another potential problem is the form release agent that was used on the form boards. Many releases contain volatile chemicals that may have a noticeable odor or even increase the flammability of the lumber.