Walls must dry from the inside out after being exposed to flood water. The interior framing of walls must be thoroughly dried. Depending on the duration of flooding and the building materials and type of construction of the house, this process may take weeks or even months!
Try to remove mud and water quickly. Surface dry materials with heat and air within 24 - 48 hours. Quick drying and removal of contaminated items may help to prevent the onset of biological contamination or mold growth.
The total drying time depends on the type of materials used to build the house. It also depends on the amount of air circulation and the moisture content of the air. Drying times can be significantly reduced by continuous circulation of heated air over the wet surfaces. Dehumidification will also help.
To immediately release the water and mud from wall cavities, remove interior wall finishes and insulation. All wall finishes from the high water line plus any capillary rise (water that has been absorbed upward) should be removed and discarded. Capillary action is very strong so this could be as much as 1 ½ feet above the high water line - maybe more. If you measure, see or feel moisture, remove that portion of the wall and discard it.
All insulation that has become wet MUST be removed to facilitate rapid drying. It should then be discarded as it will be contaminated. Most insulating materials are adversely affected by water. Even though plaster may survive brief water exposure, the wall cavity must be dried quickly. This helps prevent contamination and potential decay of wood framing members. Remember, any insulation in the wall cavity that is wet must be removed immediately and discarded.
With proper cleaning, disinfecting and refinishing, it may be possible to salvage trim and wall finishes that are made from solid wood. Most paneling will need to be discarded.
A moisture meter can be used to identify wet walls. If you have access to one, you can more readily determine wet walls and finishes. If you don't have a meter, be conservative about what materials to keep. Discard anything you aren't sure about. The moisture meter is also helpful in determining when walls are dry enough to re-insulate and close up.
Moisture meters may be available at building supply stores and through home inspectors. You may also find them on the web. The Minnesota Department of Public Health has a list of Indoor Air Quality service providers. The information number is 1-800-789-9050.
Reviewed by Dick Stone April 2011
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