Why has my worktop joint opened up, and can I close it again?
Reading the joint to work out whether the bolts have slackened, the units have moved, or the core has already swollen — and which of those can be fixed.
- Difficulty
- intermediate
- Time
- 1 hr 30 min
- Read
- 5 min
Short answer
Get under the worktop and check the connector bolts first: they slacken, and a joint that has simply opened often closes again with a quarter turn on each. If the edges of the joint are raised and swollen rather than parted, water has got in and the core has expanded — that cannot be pulled back together and the section needs replacing.
Do this first
A worktop joint that has opened is telling you one of three things: the bolts have loosened, the units under it have shifted, or the core has swollen. Only the first two are recoverable, and telling them apart takes two minutes with a torch, so it is worth doing before spending anything.
What you'll need
- Spanner or socket to suit the connector bolts
- Torch
- Straight edge
- Worktop jointing compound, if remaking the joint (optional)
- Spirit level
Step by step
- Run a finger along the joint and read what you feel.A gap you can see into, with both surfaces still flat and level, is a mechanical problem — bolts or units. A ridge, where the material either side of the line stands proud, is swelling, and swelling is water damage.
- Empty the cupboard and get underneath.The three connector bolts are in recesses in the underside, spanning the joint. You need a torch and room to get a spanner or socket on them.
- Try the bolts before anything else.Nip each one up in turn — back, middle, front — and watch the joint from above as you do. If it closes, the fix may be that simple. Do not overtighten: the nut is pulling against chipboard and it will crush its pocket.
- Check the units under the joint are still level and tight.A corner unit that has settled on a leg, or connecting screws that have loosened, lets the two worktop pieces move relative to each other. Level the units first — otherwise you tighten a joint into a distorted position.
- Check whether the worktop is still screwed down.The worktop is fixed to the units' top rails from underneath. Screws that have pulled out let the top lift and the joint work. Check every fixing along both pieces near the joint.
- Look at the joint line for signs of water.Dark staining along the line, a slightly raised edge, or laminate that has lifted at the very edge of the joint all mean the core has taken water. That is the point where tightening stops helping.
- Decide between remaking and replacing.A dry, mechanically open joint can be taken apart, cleaned, re-compounded and re-bolted, which is a good afternoon's work and gives a proper result. A joint whose core has swollen cannot be remade — the material has expanded and will not go back.
- If remaking, take it apart properly.Unbolt, lift the smaller piece clear, scrape the old compound off both faces down to clean material, dry thoroughly, re-seal the cut edges, apply fresh compound to both faces, reassemble and follow the tightening order — front bolt last.
- Re-seal everything around the joint afterwards.The joint failed because water reached it. Check the sink seal, the tap hole, the worktop-to-wall junction and the front edge, and put right whatever let the water in, or the new joint goes the same way.
Tips
- A joint that opens seasonally, closing in winter and gaping in summer, is usually a timber worktop moving with humidity rather than a fault. Solid wood tops are jointed with that movement allowed for.
- If the bolts have crushed their pockets and no longer pull, a repair plate — a steel plate screwed across the underside of the joint into both pieces — can hold a joint that is otherwise sound.
- Take a photo down the joint line before and after tightening. Small movements are hard to judge by memory.
If it doesn't work
Visible gap, surfaces still flat and level
Cause: Connector bolts have slackened — Fix: Tighten each bolt a little at a time, back to front, checking the joint from above. Do not overtighten — the nut bears on chipboard.
Joint open and one surface higher than the other
Cause: The units below have moved, or the biscuits have failed — Fix: Level the units first, then slacken the bolts, level the two surfaces with a straight edge, and retighten front last.
Raised ridge either side of the joint line
Cause: Water in the chipboard core, which has swollen — Fix: Not recoverable. The swelling is permanent expansion of the board. That section of worktop needs replacing, and the source of the water needs finding first.
Joint keeps reopening after tightening
Cause: Bolt pockets have crushed, or the worktop is not fixed down to the units — Fix: Check the worktop fixings into the top rails. If the pockets have gone, a steel repair plate screwed across the underside will hold it.
Dark line along the joint
Cause: Water has been sitting in the joint, and the compound has failed or was never there — Fix: If the core is still firm, remake the joint with fresh compound. If it is soft or raised, it is too late.
Questions people ask
Can a worktop joint be tightened?
Yes. Three connector bolts sit in recesses in the underside spanning the joint, and they do slacken over the years. Tighten them a little at a time, back to front, watching the joint from above.
My worktop joint is raised at the edges — what does that mean?
Water has reached the chipboard core through the joint and the board has swollen. That expansion is permanent and cannot be pulled flat. The section has to be replaced, and the water source found first.
How do I stop a worktop joint failing again?
The joint has to be assembled with worktop jointing compound on both cut faces, which is a waterproof gasket rather than a glue. Then keep water out of the joint from above — the sink seal, the tap hole and the wall junction are the usual routes.