Plaster does better than drywall when water leaks
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Q: We recently had our roof replaced. When it was torn off and covered by tarps, we had a major storm. As a result, there was water damage to the plaster walls and ceiling on the upper floor. The contractor brought out dehumidifiers. Should we be concerned about persistent water in the attic? Should we be concerned about the plaster ceilings? Also, we have blown-in insulation. Will it be a reservoir for mold and mildew? Should we have it replaced?
A: Plaster is cement-based, whereas drywall is gypsum. When exposed to water, gypsum readily loses its structural integrity. Drywall also has double-sided paper facing, that paper being a food source for mold — allowing it to grow more easily both inside and outside a wall.
With heavy saturation, drywall should generally be replaced, but plaster may be dried out successfully. With plaster, the water stains may extend a great distance away from the source (because of wicking), but the cement will absorb and dissipate the moisture over time, somewhat like stucco siding will.
If the plaster ceilings and walls have major cracking, are holding water or have buckled, then those sections will need repair. Allow the plaster several weeks to dry (with heat on in all rooms) after using the dehumidifier, repair all physically damaged areas, seal the stains with a water-damage sealer such as Kilz, and paint it.
The wood framing members in the attic and the studs are likely going to dry well and suffer no permanent damage from a short-lived dousing. If the attic is well-ventilated, and the leaks are stopped, you have no worries, although it should be inspected within a few weeks for any lingering mildew growth. Treat with a 1-to-4 bleach/water solution if any is found.
The insides of the exterior walls may hold moisture if insulated. This is the most risky area for mold growth. Remove the baseboards and electrical outlet plates, cut away some plaster that is covered by these items, and inspect inside the wall with a mirror, using a finger to feel for dampness when possible. If the plaster wall is insulated and is soaked, it should be cut open near the bottom wide enough to pull out the insulation from each stud cavity. The wall will dry out on its own when open to the air and the insulation is gone. Insulation can be replaced after the wall dries. If it's drywall, it should be removed and replaced entirely to reduce the risk of mold.
Attic insulation that has been wet should be removed and replaced, not only because of water retention and mildew issues, but also because of a future inability to retard heat loss.
Q: What to do about a high water table? I've noticed water rising above the Visqueen, but no leakage through the foundation. All my downspouts have been placed to discharge 15-20 feet away from the house, so that is not the issue. Should I install a drainage system in the crawlspace and build a pit for a sump pump? Or add 4-5 inches of sand/dirt to the crawlspace? Or??
A: Interior drainage systems are one possibility. If you cannot access the exterior due to landscaping or walkways, have a high water table, or have other issues preventing you from eliminating water entry in the first place, interior systems can and do work well.
A sump pump down inside a lowered pit with drainage ditches leading to it is certainly feasible and inexpensive, although it will become a maintenance item (cleaning and pump replacement) and carries a stigma at resale time. Sump pumps don't work during power failures.
Adding several inches of pea gravel (not sand or dirt) can be very expensive, depending on accessibility, but will require no maintenance (be sure to put the Visqueen back in place). If the home is in a river valley, this might be a good alternative if a documented level of regular water-table change can be shown.
Be sure to check with the local authorities for restrictions if in a frequently flooded area. Also beware of clearance issues when raising the level. Current code requires 18 inches of clearance generally and 12 inches below beams.
Many specialized waterproofing companies offer interior drainage systems inside basements, some utilizing proprietary materials and techniques. Typically the concrete is cut and a trench is cut parallel to the foundation wall, with a drainage system added at the base of the foundation.
Water always takes the path of least resistance — this drainage system allows water to drain beneath the foundation more easily into the system than leak into or through other undesirable areas.
My feeling is that this type of system is like putting a Band-Aid on cancer (treating the symptom, not the cause), but I will say in their defense that these companies do indeed warranty their work, and they are generally very effective. And sometimes, interior systems are the only, or only economically feasible, alternative.
Darrell Hay answers readers' questions. Call 206-464-8514 to record your question. Or e-mail dhay@seattletimes.com. Sorry, no personal replies.