Why has my worktop swollen at the sink, and can it be repaired?

This is the most common terminal failure in a British kitchen, and it is entirely preventable. A laminate worktop is a chipboard core with a decorative skin on the top face only. Every cut edge is raw, the sink aperture is the biggest cut edge there is, and it sits directly under the wettest part of the kitchen.

What you'll need

• Torch
• Clear neutral-cure silicone
• Sealant remover and a scraper (optional)
• PVA-based or clear edge sealer
• Kitchen roll, for finding the leak

Step by step

1. Accept the diagnosis before spending money.A raised, spongy or ridged area along the edge of a sink cut-out is swollen chipboard. It is not lifted laminate, it is not a finish problem, and there is no filler, resin or clamp that returns expanded board to its original thickness.
2. Find out whether it is still getting wet.Dry everything thoroughly, then lay kitchen roll along the underside of the aperture edge and in the cupboard below, and use the kitchen normally for a day. Wet paper tells you the leak is live and where it is.
3. Check route one: the sink rim seal.Run a fingernail round the joint between the sink rim and the worktop. Any gap, any lifted edge, any place the bead has shrunk away, is a route straight to the cut edge. This is the commonest one by a long way.
4. Check route two: the tap hole.Water runs down the outside of a tap body, past the base washer, and into a hole whose cut edge is raw. A perished or missing washer under the tap base, or a tap that has worked loose, feeds this constantly.
5. Check route three: the worktop joint.A mitred joint assembled without compound wicks water along the whole line. If the swelling extends towards a joint rather than sitting purely around the sink, this is likely.
6. Check route four: from below.A weeping tap tail, a leaking waste connection or a dishwasher hose in the cupboard wets the underside of the worktop, which is also raw chipboard. Check the cupboard base for staining and the underside of the top for dampness.
7. Fix the source before anything else.There is no point replacing a worktop that will be soaked again by the same leak. Reseal the sink, replace the tap base washer, tighten or replace the failing connection.
8. Seal every cut edge on the new worktop, before the sink goes in.This is the whole prevention. A continuous film of clear silicone or a proprietary edge sealer over the full depth of the aperture edge, including the underside lip, plus the tap hole edge and both ends of the run. Ten minutes.
9. Bed the sink on a continuous bead and let the clips compress it.A continuous ring of neutral-cure silicone under the sink rim, then the clips pulled down to squeeze it. The clips hold the sink; the silicone is what keeps water out. Silicone smeared round the outside afterwards is not the same thing.
10. Consider whether a different material is the answer.If this has now happened twice, or the kitchen is heavily used, compact laminate, solid surface or stone removes the failure mode entirely because there is no absorbent core.

Tips

• Replacing one length of a laminate worktop is much less expensive than people assume, and matching a current stock pattern is often possible. It is worth pricing before assuming the whole kitchen is involved.
• If a small swollen area is at the very back where nothing will be replaced for a year, a bead of clear sealant over it at least stops it getting worse. It is triage, not repair.
• The cheapest insurance in a kitchen is a fortnightly look under the sink with a torch. Almost every worktop failure at a sink was a slow weep for months before it became visible above.
• When a new sink or tap goes in, seal the cut edge even if the old one was never sealed. It is the moment when the edge is accessible and dry.

Common mistakes

• Trying to dry and clamp swollen chipboard flat — The chips have absorbed water and expanded individually. Drying them does not shrink them back and clamping just crushes them. The material is dimensionally different from what it was.
• Sealing over the top of the swelling and calling it fixed — The water is usually still getting in from underneath or from the rim, and the swelling continues under the sealant where you cannot see it.
• Fitting the replacement without sealing its cut edges — You have just repeated the exact process that destroyed the first one, and you will be doing this again.

Questions people ask