How do I repair a water damaged laminate board?

Why swollen laminate cannot be dried out, how to replace a board mid-floor, and what has to happen before any repair.

Difficulty: intermediate
Time: 2 hr
Read: 4 min

Short answer

A swollen laminate board cannot be recovered — the fibreboard core has expanded permanently. Fix the water source, dry the subfloor completely, then replace the affected boards either by unclicking from the nearest wall or by cutting one out mid-floor.

Laminate is high-density fibreboard with a printed layer on top. Once water reaches the core through a joint or an edge, the board swells and the swelling does not go back.

What you'll need

Spare boards
A circular saw or a plunge saw
A chisel and a multi-tool
Wood glue for the replacement joint
A dehumidifier or fan
A moisture meter

Step by step

Find and fix the water source.A dishwasher, a washing machine hose, a radiator valve, a leaking shower tray, a failed threshold. Replacing boards while water is still arriving is wasted effort.
Lift the affected boards promptly.Water spreads under a floating floor far beyond the visible damage. Getting the boards up quickly limits how much of the subfloor and underlay is affected.
Dry the subfloor properly.Fans, a dehumidifier and time. A moisture meter or the polythene test tells you when it is genuinely dry, which is usually days rather than hours.
Replace the underlay in the wet area.Foam underlay that has been soaked holds water against the boards and can go mouldy. It costs very little to replace.
Count the damaged boards.Any board that is swollen at a joint, has a raised edge, or has a soft core is finished. Include boards that look only slightly affected — they get worse.
Choose the removal method.If the damage is within a few rows of a wall, take the beading off and unclick the rows back to it. That is the neat method and it lets the boards go back properly.
Cut out mid-floor if unclicking is impractical.Set a circular or plunge saw to just the board thickness, cut a rectangle 40mm inside the board's edges, lever the middle out, then chisel the remaining edges free.
Prepare the replacement board.Cut the lower lip of the groove off the replacement's long side and the end, so it can drop in from above rather than needing to slide in.
Glue the modified joints.A bead of PVA on the cut joints, because the mechanical lock has been removed on those edges. Weight the board while it sets.
Check the colour match.Boards from a different batch, or unfaded new boards next to a floor that has had five years of sunlight, will show. Take replacements from under a sofa or a cupboard if you can.
Re-check the expansion gap.While the floor is open, confirm the perimeter gap and any pinch points, since a wet floor that has swollen may have pushed against them.

Tips

Water-resistant laminate exists and is worth specifying in kitchens and by external doors. It is not waterproof, but it survives a spill that would destroy standard laminate.
Keep four or five spare boards from any flooring job in the loft. Ranges are discontinued constantly and a mid-floor repair depends on having a match.
Silicone at the perimeter under the beading in a kitchen or bathroom stops spills getting under the floor at the edges, which is where most of it gets in.

Common mistakes

Trying to dry a swollen board out — The fibreboard core is compressed wood fibre and resin. Water breaks the resin bond and the fibres expand irreversibly, so drying leaves a permanently swollen, weakened board with a lifted edge.
Replacing the boards without drying the subfloor — Trapped moisture under a new floating floor has nowhere to go. It re-wets the new boards from below, and it can produce mould in the underlay that only becomes obvious as a smell months later.

If it doesn't work

Edges of boards raised and rough

Cause: Water into the core through the joint — Fix: Replace the boards; the swelling is permanent.

Damage keeps spreading

Cause: Water source not found — Fix: Stop and trace the leak before any further repair.

Musty smell but no visible damage

Cause: Wet underlay under an intact floor — Fix: Lift a section at the nearest wall and check; replace wet underlay.

Replacement boards a different shade

Cause: Batch difference or UV fading of the original — Fix: Take replacements from a hidden area and patch the hidden area with the new boards.

Questions people ask

Can water damaged laminate be sanded flat?

No. The visible surface is a printed layer a fraction of a millimetre thick. Sanding a swollen edge goes straight through it and leaves a pale patch that looks far worse.

Is engineered wood the same?

No — engineered wood has a real timber wear layer and can often be dried, sanded and refinished. That is one of the main practical arguments for engineered wood over laminate in a kitchen.