You run a hand along the worktop and feel a slight ridge at the joint nearest the sink, and looking closer the seam has darkened and the surface has lifted very slightly compared to the rest of the run.
This is water damage, specifically water that has found its way into the board's core through the joint rather than staying on the surface. The swelling itself won't reverse, so identifying and stopping the water source is the priority before it spreads any further.
Symptom versus cause
The swelling and darkening is the board reacting to moisture it has absorbed — it's not the leak itself. Fixing the visible swelling without finding where the water is entering just means it happens again, usually spreading further along the same joint.
Causes, in order of likelihood
The location — right beside a sink or hob — narrows the likely causes considerably.
- Water tracking directly into an unsealed or poorly sealed joint from daily use around the sink
- Cut-outs, for the sink or hob, left with raw, unsealed edges that draw in water like a sponge
- A failed seal around the sink itself, letting water run underneath rather than into the bowl
- The wrong board specification used for a wet zone in the first place, without adequate water resistance
How to tell the causes apart
Check exactly where the swelling starts relative to the sink or hob cut-out. Swelling that begins right at the cut-out edge and spreads outward points to an unsealed cut-out or a failed sink seal rather than the joint itself.
Run a hand around the sink's edge for movement or a spongy feel in the sealant — a loose or perished seal will often show signs of water having sat there.
Establish what the worktop material actually is. Some board substrates are far more vulnerable to swelling once water gets in than others, and if a moisture-sensitive board was used right next to a sink, repeat swelling elsewhere along the run becomes more likely.
Self-diagnosis before booking a repair
Run a fingertip along the joint and the cut-out edges to feel for any softness or unevenness beyond the visible swelling, since damage sometimes extends further under the surface than it appears from above.
Check how quickly water is wiped away around the sink after use, and whether standing water is routinely left to sit at the joint overnight — this doesn't change the diagnosis, but it's useful information for whoever assesses the extent of the damage.
Why this fault tends to come back
Where only the visible swollen strip is replaced without resealing the wider cut-out or refitting the sink properly, the same water route into the board is usually still there, and swelling reappears along the new joint within a similar timeframe.
Worktops in a wet zone that are wiped over quickly but never fully dried around the joint see water repeatedly finding the same small gap in a seal, which is why sealing quality at the time of the repair matters as much as the board replacement itself.
Common questions
Will the swelling go down if I dry the area out?+
No — once a board has swollen from absorbed moisture, it does not shrink back to its original shape or thickness even once it dries. The affected section needs replacing rather than dried out and left.
Is this covered by a kitchen fitter's guarantee?+
That depends entirely on the individual fitter's terms and how the damage occurred, so it's worth checking the original paperwork. What matters practically is identifying and stopping the water source regardless of who ends up carrying out the fix.
Can I just seal over the swollen area myself?+
Sealing the surface doesn't reverse swelling that's already happened inside the board, and it does nothing about the water still finding its way in if the underlying cause — an unsealed cut-out or failed sink seal — hasn't been fixed.
Book a free assessment of your worktop damage
We'll identify exactly where the water is getting in and tell you honestly how much of the worktop needs replacing.