Wet drywall: save it or replace it

What kind of water was it? How long has it been wet? Is the board soft, swollen or peeling? Is there wet insulation behind it? Insulation holds water against the wall and usually means opening it.

See water damage categories explained for the first question.

Wet ceiling board can fall without warning, so treat any sag as a hazard. Keep people out from beneath it. Older walls may contain lead paint or asbestos, which should be tested before cutting.

Keep drywall when the water was clean, it was caught quickly, the board is firm and flat, and the cavity behind it can be dried. Replace it when the water was contaminated, when the board has swollen, crumbled or come loose, when wet insulation sits behind it, or when mold has started.

EPA gives a helpfully direct test for clean-water events. Wallboard with no obvious swelling and with seams intact may be dried in place. If not, EPA says to remove, discard and replace it, and to ventilate the wall cavity if possible. Keep in mind that this table covers clean water and a response within 24 to 48 hours. If the wall has been wet longer, or mold is present, the agency sends you to its mold remediation guidance instead.

Drywall is a thin sheet of gypsum between two layers of paper. The gypsum weakens when wet, and the paper is food for mold. So the question is really whether the core has kept its strength, and whether the paper has dried before anything could begin to grow on it.

A wall is a sandwich. The board may be wet on the room side and much wetter on the back. Insulation, framing, sheathing and sometimes a vapor barrier are all in there, and none of them dry quickly when the wall is closed.

Fiberglass and cellulose insulation both appear in EPA's list as materials to discard and replace if they get wet. In practice, this often settles the question. When a wet exterior wall has insulation in it, opening the wall may be necessary, and then the board has to come off regardless of how firm it was.

Interior partition walls are easier, as they often have no insulation. Contractors may be able to dry them by removing the baseboard, drilling small holes near the bottom of the wall, and pushing air into the cavity. The same principle is what you can see on the structural drying page. Whether that fits depends on the source of the water, wall construction and readings.

When drywall has to go, it is usually cut in a straight horizontal line above the highest wet point. People call this a flood cut. Common practice is to cut somewhat above the water line, since drywall wicks moisture upward beyond what you can see. The exact height depends on readings and water type, so don't accept a figure without seeing numbers.

Cutting along a straight line makes for neater repairs, and a cut that lands on a framing stud or at a sensible height can make patching simpler. Before any cutting, find out what's behind the wall. Turn off power to any circuits in that area, watch for wiring and plumbing, and use a cutting depth that goes through the board without reaching deeper.

Lead paint and asbestos are real issues in older buildings. EPA warns that sanding or demolishing pre-1978 surfaces can spread lead dust. Contractors working in those homes must use lead-safe practices. Older joint compound and some other materials may contain asbestos, so test before cutting if there is any doubt.

Ceilings fail differently. Water pools on top of the board, adds a great deal of weight, and softens the gypsum from above. A wet ceiling can come down with little warning and bring wet insulation with it. Stay out from under any bulge, move what you can out of the room, and do not poke it unless someone has told you it is safe and you are prepared for what comes out.

Clean-water ceilings can sometimes be dried if they have not sagged and if insulation above them can be dealt with. Sagging, discolored or repeatedly wet ceilings are generally replaced. In some attic ceilings, loose blown-in insulation must be removed first, since it holds water on the board.

Find the source too. Stains on a ceiling can be a long way from where the water started, since it may run along a joist or pipe. If it is under a bathroom, think plumbing. If it is at the top floor and worse after rain, think roof.

Do not paint over mold. Absorbent materials can have mold growing into their spaces and crevices, which makes it difficult to remove, and EPA says such items may need to be thrown away. Drywall paper falls squarely into this group, so moldy board is generally cut out, not cleaned.

EPA's general line for homeowners is about 10 square feet of growth. Under that, you can usually handle it yourself. Over it, or where water damage is extensive, consult EPA's larger guidance. Consult a professional if the source was sewage or other contaminated water, and speak with a health professional first if you have health concerns. Cutting moldy drywall disturbs spores, so if you do it yourself, wear protective gear and avoid spreading dust through the home.

A musty smell without visible growth may mean mold is growing on the back side of the board. EPA lists this among common hiding places. The mold prevention page has more on that.

Whether wet drywall is covered depends on your policy and on the cause of the water. Ask your agent or insurer, because this is background and not insurance advice. It often helps to photograph walls before cutting, keep notes of readings, and keep a small sample of removed board if you are told to.

Some jobs have repair questions about how much of a wall has to be redone to look right. Your policy and your adjuster's assessment affect that answer. The adjuster guide covers how to raise those questions and what to prepare for them.

Replacing wet drywall rarely means replacing a whole room. Most repairs cut out the wet section, usually in a straight line, and tie new board into what remains. Keeping sound board makes for a smaller job, although a skilled finisher is needed to hide the joint, particularly on smooth walls and under strong side light.

You may want to go further in some cases. If a large part of the wall is affected, or the old surface is uneven, it can be easier to replace a whole sheet than to patch. Texture-matching can be difficult as well. Ask how the repair will look when the room is painted, and whether the whole wall or the room needs repainting so the color matches.

Keep cut lines sensible. A cut at a stud gives the new board something to attach to, and a cut high enough to clear all wet material saves you from cutting again. Ask the contractor to explain why they've chosen that height, using the readings they took.

Local humidity and the age of the housing can sway how a wet wall is handled. See Oregon, Connecticut, Delaware, Kansas, Louisiana, New Hampshire, Chicago, Dallas, Colorado Springs, Cedar Hill, Lake Stevens, Norcross, Port Charlotte, Prosper, Atlanta, Indianapolis.