How structural drying works after water damage

The goal

A building that has been wet needs to be returned to its normal, dry condition before mold grows and materials are damaged for good. Wiping up the puddle is the easy part. The water that matters has soaked into drywall, wood, subfloor and concrete, and it will not leave quickly without help.

The restoration industry follows a published standard for this work, the ANSI/IICRC S500. What follows is the process in plain terms.

Step 1: Assess

Before any equipment goes in, the crew works out three things.

The source and the kind of water. Clean water from a supply line, grey water from an appliance or overflow, or contaminated water from a sewer or outdoors. This decides what may be dried and what must be removed.

How far it went. Water travels under walls, under flooring and down through ceilings. Moisture meters and thermal cameras map the wet area, which is nearly always larger than what you can see.

What is wet. Carpet and drywall give up water quickly. Hardwood, plaster and concrete hold it and release it slowly.

Hazards are checked too: electricity, sagging ceilings, and in older buildings the possibility of asbestos or lead in materials that may need cutting.

Step 2: Extract

Liquid water is removed with pumps and truck-mounted or portable extractors. Weighted extraction tools squeeze water out of carpet and pad.

This step matters more than any other. Removing water as liquid is many times faster than evaporating it. Every litre left behind is a litre the drying equipment has to deal with.

Step 3: Remove what will not dry

Some materials come out so that the rest can dry:

• Carpet underpad
• Wet insulation
• Drywall that is swollen, sagging or contaminated
• Laminate flooring and underlay
• Swollen particleboard and MDF
• Baseboards, to open the bottom of the wall

With clean water and prompt action, crews try to dry in place and save as much as they can. With contaminated water, porous materials are removed.

Step 4: Evaporate

Air movers are the low, snail-shaped or flat fans you see in a drying job. They push a fast layer of air across wet surfaces, which strips away the damp air at the surface and speeds evaporation.

Specialised setups direct air where it is needed:

• Wall cavities are dried through holes drilled behind the baseboard line, or with systems that push or pull air through small ports.
• Hardwood floors are dried with mats sealed to the surface that draw air and moisture up through the joints.
• Under cabinets, air is ducted through the toe-kick space.
• Ceilings may be opened in sections, or vented.

Step 5: Dehumidify

Evaporation only moves water from the materials into the air. If the air is not dried, the room becomes a sauna, evaporation stalls, and moisture settles into things that were not wet before.

Dehumidifiers pull that moisture out of the air.

• Refrigerant dehumidifiers condense moisture on a cold coil. The low-grain type used in restoration keeps working at lower humidity than household units.
• Desiccant dehumidifiers absorb moisture with a chemical wheel. They work well in cool conditions and on dense materials.

The water collected is pumped to a drain. The amount of equipment is calculated from the size of the space and how wet it is. Too little, and drying drags on. The area is usually closed off so that the equipment is drying the building and not the outdoors.

Step 6: Control the temperature

Warm air holds more moisture, and warm materials release it faster. The space is kept comfortably warm. Extra heat is sometimes directed at stubborn materials. Too much heat too quickly can damage wood and finishes.

Step 7: Monitor

This is what separates drying from running fans.

• A dry standard is set by measuring unaffected materials of the same type in the same building.
• Moisture content of the wet materials is read each day and recorded.
• Air temperature and humidity are measured in the wet area, in an unaffected area, outdoors and at the outlet of each dehumidifier, to confirm the equipment is working.
• Equipment is moved, added or removed as areas dry.

The job is finished when the wet materials reach the dry standard. The equipment comes out when the readings say so, not after a fixed number of days.

How long it takes

• Carpet and drywall, clean water, caught early: commonly about three days
• Typical house leak with wet framing and subfloor: three to five days
• Hardwood floors, plaster, concrete, or long-standing water: a week or more
• Contaminated water: removal and cleaning come first, then drying of what remains

See how long it takes to dry a flooded basement.

Living with it

• The equipment is loud and runs day and night. Do not switch it off. Each pause sets the job back.
• It makes the area warm.
• It uses a fair amount of electricity. Several machines on one circuit can trip a breaker, so they are spread across circuits. Insurers will often consider the extra power cost as part of a claim, so ask.
• Keep doors and windows in the drying area closed unless told otherwise.
• Keep children and pets away from the machines and hoses.
• Expect a daily visit for readings.

Most people can stay in the house during a clean-water job. With sewage, heavy mold or extensive demolition, it may be better to stay elsewhere.

What you should receive

• A description of the source and the category of water
• A sketch or list of the affected areas
• Daily moisture and humidity readings
• A record of the equipment used and for how long
• Notes on what was removed and why
• Confirmation that the dry standard was reached

Insurers ask for these records, and they are useful to you as proof that the job was done properly.

After drying

Drying returns the structure to dry. It does not put it back together. Reconstruction follows: insulation, drywall, flooring, trim and paint.

More: water damage restoration.