How to prevent mold after water damage

The clock

Mold spores are in every house, all the time. They need three things to grow: something to feed on, a suitable temperature and moisture. Houses provide the first two. Add water and the only question is time.

Health Canada notes that mold begins to grow within 48 hours where there is excess moisture, and the general public health advice is to dry wet materials within 24 to 48 hours. Warm conditions, dirty water and materials such as drywall paper and carpet underpad shorten the margin.

So prevention is not a product. It is getting things dry quickly, and removing what cannot be dried quickly.

Hour one: stop and make safe

1. Stop the source. Shut the valve, or the main.
2. Electricity. Do not walk into water where outlets, cords or appliances are wet. Switch off the affected circuits if the panel is reachable and dry.
3. Identify the water. Clean supply water gives you the most options. Water from a drain, a sewer or outdoors is contaminated, and the rules change: porous materials it touched are removed.
4. Photograph everything for your insurer.

Hours one to four: get the water out

• Extract standing water with a wet vacuum, a pump or mops. Extraction removes far more water, far faster, than evaporation ever will.
• Lift rugs and take them out to dry.
• Move furniture off wet flooring, or put foil or plastic under the legs.
• Take wet boxes, papers, books and fabrics out of the area. Cardboard and paper mold fastest of all.
• Open cupboards and drawers in the affected area.

The first day: decide what goes

Some materials cannot be dried quickly enough, or cannot be dried at all in place.

Usually removed

• Carpet underpad
• Carpet that was wet for more than a day or two, or wet with contaminated water
• Drywall that is swollen, sagging, or soaked through, and any drywall wetted by contaminated water
• Wet insulation in walls and ceilings
• Laminate flooring and its underlay
• Particleboard and MDF that has swollen
• Ceiling tiles
• Mattresses and upholstered furniture that were saturated

Usually dried in place

• Concrete and masonry
• Solid wood framing
• Plywood subfloor that is sound
• Drywall that is damp but firm, with clean water, where the cavity behind can be dried
• Solid hardwood flooring, with the right equipment
• Carpet wetted briefly by clean water, with the pad replaced

Removing baseboards and drilling or cutting openings at the bottom of walls lets air into the cavities, where water collects and mold starts unseen.

Days one to four: dry properly

Dehumidify. Air movement alone only moves moisture from the materials into the air. A dehumidifier takes it out of the house. Restoration contractors use large refrigerant or desiccant units sized to the space. A household dehumidifier helps with a small job.

Move air across wet surfaces. Air movers speed evaporation from floors, walls and cavities.

Keep the area closed while dehumidifiers run. Opening windows helps only when outdoor air is drier than indoor air, which in a humid Ontario summer it often is not.

Keep it warm, not hot. Normal room temperature suits the equipment.

Run the equipment continuously. Turning it off at night to sleep lengthens the job and gives mold its chance.

Measure. A moisture meter reads what is happening inside materials. Readings are taken daily and compared with dry materials of the same kind elsewhere in the house. Drying is finished when they match. Dry to the touch is not dry.

Most clean-water losses dry in about three to five days with proper equipment. Thick materials, hardwood and concrete take longer.

Common mistakes

• Waiting for the insurer before starting. Policies expect you to prevent further damage. Report the claim and begin.
• Leaving wet underpad under carpet that feels dry on top.
• Leaving baseboards on, trapping water at the bottom of the wall.
• Using fans only, with no dehumidifier.
• Stopping when surfaces feel dry.
• Painting or closing up before readings are normal.
• Spraying bleach or a mold product and assuming that takes care of it. Chemicals do not dry a wall.
• Turning up the heat without removing the moisture, which makes a warm, humid room.

What about antimicrobial sprays?

Restoration contractors sometimes apply an antimicrobial product to framing and subfloors after contaminated water, or where drying will take longer. It can slow growth on the treated surface for a time. It is not a substitute for removing wet materials and drying, and public health guidance puts the weight on drying and removal.

Hidden places to check

• Inside wall cavities, especially behind baseboards
• Under cabinets and behind toe-kicks
• Under and behind appliances
• Under floating floors
• The ceiling and cavity below an upstairs leak
• Closets on the other side of a wet wall
• Inside floor ducts
• Under stairs

How to tell it worked

• Moisture readings back to normal in all affected materials
• Indoor humidity back to its usual level
• No musty smell in the following weeks
• No staining, bubbling paint or swelling appearing later

Keep the drying records and readings if a contractor did the work. They are useful to your insurer and to a future buyer.

If it is already past 48 hours

Start anyway. Treat porous materials that have been wet for days as likely to be moldy: remove them carefully, bag them, and do not run the furnace fan while doing so. If growth is visible over more than a small area, or the water was contaminated, get professional help. See how fast mold grows after water damage.

More: water damage restoration and mold removal and remediation.