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Michigan State University Extension
Home Maintenance And Repair - 01500014
06/24/03


Drying Walls After A Flood



Inner Walls
Walls must dry from the inside out. The interior framing of walls should be allowed to dry thoroughly. Sometimes this process takes weeks or even months. To release water and mud from walls remove top and bottom strips of siding on the outside of the building. Drill several holes in walls near the inside floor line.

The total drying time will depend partially on the amount of dry air that can circulate through the studding (called "chimney action"). To provide for maximum chimney action, first consider the construction of the building.

Fire Stops or Cross Bracing
These are horizontal or diagonal braces between the vertical supports or studs.

Cross bracing will prevent chimney action between the studding. However, cross bracing is not usually found in modern construction, except in two-story houses where is has been specified. To allow free air movement, remove interior or exterior wall covering wherever cross braces are located. To check for cross bracing or fire stops, extend a stiff wire into the wall cavity.

Insulation
Any types of insulation will be ruined if water- soaked. You will probably have to replace flood-soaked insulation.

1. Loose fill (such as vermiculite) will settle to the bottom of walls. As it dries it can be removed. If not removed, loose fill insulation will create odors and eventually cause decay of the studding.

2. Rock wool batting insulation will also bunch and settle. If it is absorbent it will create odors and could eventually cause studding decay.

3. Fiberglass batting will also bunch, but will not develop odors. Its insulating value will be greatly reduced.

4. Reflective surfaces (such as aluminum foil) will probably lose their reflective ability thus decreasing their insulating effectiveness. The material itself should be undamaged.

Wall Coverings and Finishes
1. Plaster will take weeks or even months to dry but may not be ruined by water. Old plaster, however, may disintegrate after being wet for a long time.

2. Dry wall (plaster board) will warp and disintegrate in water. Warping above the water level can also be expected. Drywall that has been submerged must be replaced.

3. Laminated paneling (plywood, masonite) will separate and warp above and below the water level. The extent of damage will depend on how long the paneling was submerged, and how quickly moisture is removed from the studding. Slow drying decreases the possibility of delamination.

Siding
1. Masonry will dry slowly but will be undamaged except for possible cracking or settling. Open inside walls to prevent mildew and decay of wooden supports.

2. Lapped siding (wood, asbestos, aluminum). Remove strips or sections to dry insulation and studding. The type of sheathing will determine drying rate. To prevent oxidation, make sure backing of aluminum siding is dry.

Sheathing (material between studding and finish siding)
1. Wooden boards will dry slowly and some will warp. If possible, renail warped areas before they dry. Replace those that are too badly warped to salvage.

2. Sheathing board is usually absorbent and will be difficult to dry. Some will disintegrate or separate and must be replaced.

3. Plywood will probably separate in places and must be replaced. Marine plywood will not warp or separate, but is generally considered too expensive to use in residential construction unless the building is subjected to frequent flooding.

References

This article was written by Anne Field, Extension Specialist, Emeritus, with reference from the USDA Disaster Handbook.

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