Q: We recently purchased a condo on a lake in Alabama. The building was framed in February or March, but then construction basically halted while they finished another building that was further along. The building was without a roof for almost 6 months during this very rainy summer. The bottom was often full of water and our condo is on the bottom level, but it is on a concrete slab. The roof finally went up after 6 months, but the floors are still wet with standing water, mushy sawdust, etc. Do we need to be concerned about mold? They say they will not dry wall it in until everything is dry. What do you think?

A: Everything depends on the construction materials involved and the drying/wetting cycles that may have occurred. Are the walls wood or metal studs? Metal may rust but won't support mold. Wood frame lumber is reasonably resistant to mold but if it is actually sitting in water constantly or in a sawdust/water mix then fungal or mold growth is a possibility. Treating the frame lumber with a disinfectant and a fungal encapsulant (not bleach) would likely solve the problem. Was there insulation that got wet and what is the exterior sheathing product and did it get wet? Exterior plywood or boards may be okay but oriented strand board (OSB) or some paper faced gypsum board exterior sheathing products may be a problem. Wet fiberglass insulation should be removed. In the old days when solid wood and wood boards were used, exposure to the elements was not much of a problem as long as drying and ultraviolet light from the sun had a chance to have an effect. Many current building materials are more susceptible to microbial growth because of the loss of natural anti fungal properties that occurs in processing (example: wood to paper). It is very important that the slab is allowed to dry before flooring is installed. Specific tests for water release from concrete exist that determine whether the floor is dry enough for installation of carpeting or other flooring. A thorough cleaning of debris and sawdust is needed before any wall cavity is enclosed.

The proper use of a vapor membrane or vinyl wall covering on the interior surface of an exterior wall may also be a source of mold concerns if the building is air-conditioned (I assume it will be) and the environment is humid. It is important that finished walls can breathe. Moisture in trapped walls causes a problem. Cool air-conditioned wall surfaces with an impermeable membrane (poly or vinyl wallpaper) are a good place for mold to get established. Micro punched, breathable, wall coverings exist and of course painted walls are okay. Vapor retarding membranes (poly) should always be on the warm side of the building to minimize moisture from entering a wall cavity. Note: Building wraps are not vapor retarders; they are designed only to shed liquid water not prevent the migration of water vapors in a gaseous state.

Mark Goldman, Senior Air Quality Scientist, EFI Global, Inc.

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