Water-damaged hardwood floors: dry, refinish or replace?

What water does to wood

Wood takes in moisture and swells. When the underside of a board is wetter than the top, the bottom expands more and the edges rise. When boards swell with nowhere to go, they push against each other and lift. When wood stays wet, it stains and eventually rots.

How much of this is permanent depends on how wet the boards got, for how long, and how they are dried.

Reading the damage

Cupping. The edges of each board are higher than the centre, giving a washboard feel. This means the underside is wetter than the surface. It is the most common result of a leak, and often reversible.

Crowning. The centre of the board is higher than the edges. This usually happens when a cupped floor is sanded flat too early, and the wood then finishes drying and shrinks.

Buckling. Boards lift right off the subfloor, sometimes by several centimetres. This is severe swelling. Buckled boards rarely go back down properly.

Gaps. After drying, boards may shrink and leave gaps where they were crushed at the edges.

Staining. Grey or black marks, particularly along joints and around fasteners, where water reacted with the wood or the nails.

Finish damage. A white haze in the finish means moisture trapped in the coating. Peeling means the bond has failed.

The first day

1. Stop the water.
2. Mop and extract standing water immediately. Do not leave it sitting on the surface.
3. Remove wet rugs and furniture.
4. Run a dehumidifier and keep air moving across the floor.
5. Keep the room at normal temperature. Do not blast it with heat.

Why drying speed matters, in both directions

Too slow, and mold grows on the subfloor and the underside of the boards.

Too fast, and the wood can split and check as the surface dries and shrinks while the core is still swollen.

Professional drying of hardwood uses dehumidification and, for significant losses, mats sealed to the floor that draw air and moisture up through the joints between boards. The moisture content of the wood is measured and brought down steadily.

Do not sand yet

A cupped floor should not be sanded until the wood has returned to its normal moisture content. That can take weeks. Sanding early removes the raised edges, and when the boards finish drying the centres are left high. A flooring professional uses a moisture meter to decide when the floor is ready.

What usually can and cannot be saved

Often saveable

• Solid hardwood wet for a short time with clean water
• Mild to moderate cupping
• Surface finish damage

Usually replaced

• Buckled or split boards
• Deep black staining
• Boards wet for many days, or with mold underneath
• Floors soaked by sewage or outside flood water
• Engineered hardwood whose layers have delaminated

Solid hardwood can be sanded and refinished several times. Engineered hardwood has a thin wear layer and is less forgiving.

The subfloor

Plywood and oriented strand board under the hardwood absorb water too. If the subfloor has swollen, delaminated or grown mold, boards have to come up to deal with it. A leak that reached the floor from below, such as from a basement ceiling, should always be checked from underneath.

Matching and the extent of repair

Replacing a few boards in the middle of a room is possible, but new wood rarely matches old in colour until the whole floor is sanded and refinished together. Where a floor runs continuously through several rooms, discuss with your adjuster how far refinishing or replacement should extend to get a consistent result.

Insurance

Sudden leaks are commonly covered, including drying and repair or replacement of the floor. Long-term moisture, such as from a slow leak or a damp crawlspace, usually is not.

Solid, engineered and how the floor was installed

Nailed solid hardwood over plywood is the most forgiving. Water can be drawn out through the joints, and the boards can be sanded.

Glued-down hardwood on concrete traps water between the wood and the slab. If the adhesive bond fails, boards sound hollow when tapped and have to be lifted.

Floating engineered floors behave like laminate. Water spreads underneath, and the floor usually has to be taken up to dry the subfloor.

Hardwood over a radiant heating system needs particular care, because heat applied too quickly from below damages the boards.

Different species, different behaviour

Oak has open pores and tannins that react with water and iron, which is why it stains black around nails. Maple is dense and moves a great deal with changes in moisture. Wide planks cup more visibly than narrow strips because there is more wood across each board to swell. Exotic species vary widely. A flooring professional can tell you what to expect from yours.

Black stains from pets and plants

Not all water damage is a flood. Plant pots without saucers, pet accidents and leaking radiators produce small, deep black stains. These have penetrated the wood and often do not sand out. The usual repair is to replace the stained boards and refinish.

Living with the floor while it dries

Expect the equipment to be noisy and warm, and the room to be out of use for several days. Keep furniture and rugs off the floor so that it dries evenly, and keep the house at a steady temperature. Do not judge the floor in the first week. Cupping often looks worst just as the wood begins to dry and improves over the following weeks.

More: water damage restoration.