How do I fit a kitchen sink into a worktop?

Fitting a sink is easy in the wrong order and very difficult in the right one — which is why the order matters more than any individual step. Everything that can be assembled on the bench should be assembled on the bench, because the alternative is doing it on your back inside a base unit.

Safety

What you'll need

• The sink, with its clips and its own foam or rubber gasket
• Neutral-cure silicone and a gun
• Clear edge sealer, for the aperture cut edge
• Tap, waste kit and flexible tap tails
• Basin wrench and adjustable spanner
• Screwdriver, jigsaw, and the sink's own template if cutting (optional)
• PTFE tape (optional)
• Torch and something to lie on

Step by step

1. Check the aperture against the new sink before anything else.Sinks of the same nominal size have different cut-out dimensions. Offer the new sink to the existing hole and check it drops in with the rim covering the edge all round. A new sink needing a bigger hole in stone is a fabricator's visit.
2. Remove the old sink completely and clean the aperture.Isolate the water, disconnect the tap tails and the waste, release the clips, cut the old sealant with a blade, and lift the sink out. Then scrape and clean the worktop surface all round back to bare material — new silicone will not stick to old.
3. Seal the raw cut edge, full depth.This is the step that decides whether the worktop survives. Clear silicone or a proprietary edge sealer over the whole depth of the aperture edge, including the underside lip and the tap hole. Ten minutes, and it is the difference between twenty years and three.
4. Fit the tap to the sink on the bench.Base washer under the tap, tails threaded through, plate and nut or horseshoe bracket underneath, tightened with the tap held square. Doing this with the sink out is enormously easier than doing it inside a cupboard.
5. Fit the waste and the overflow on the bench too.Sealing washer stack in the right order, the flange bedded on the manufacturer's sealant or its supplied washer, backnut tightened evenly. Connect the overflow hose if the sink has one — it is far harder to reach later.
6. Fit the clips into their channels.Inset sinks come with clips that engage a channel or lugs on the underside of the rim and screw down against the underside of the worktop. Loosely fit them all before the sink goes in, positioned so you can reach them.
7. Run a continuous ring of silicone.Around the aperture on the worktop, or around the underside of the sink rim, in one unbroken bead. Continuous is the operative word — a bead with a gap in it is a route for water and it will find it.
8. Drop the sink in and pull it down evenly.Tighten the clips in a rotating sequence, a little at a time, like wheel nuts, so the rim is pulled down evenly and the bead is squeezed uniformly. Tightening one corner fully first tilts the sink.
9. Wipe the squeeze-out immediately.A wetted finger round the whole rim while the silicone is fresh. Left to cure, it has to be cut off, and cutting sealant off a new sink rim usually marks something.
10. Connect the tails and the waste, then test properly.Restore the water, run both taps, fill and drain the bowl to load the waste, and dry every joint. Then look again ten minutes later, and put white kitchen roll under everything overnight. Weeping joints appear on the second look, not the first.

Tips

• The clips hold the sink; the silicone keeps the water out. Neither does the other's job, which is why silicone smeared around the rim after the sink is down does not work.
• Neutral-cure silicone rather than acetoxy on stone, quartz and some metals — acetoxy releases acetic acid as it cures and can mark them.
• Fit isolating valves on the supplies while everything is apart if there are none. It turns every future tap or waste job into a ten-minute one.
• Take a photograph of the waste washer stack before dismantling the old one. The order of washers is easy to lose and the wrong order leaks.

Common mistakes

• Fitting the sink before the tap and waste — You then have to do the awkward parts lying inside a base unit with a torch in your teeth. Everything that can be done on the bench should be.
• Not sealing the aperture cut edge — It is raw chipboard in a laminate top, sitting under the wettest part of the kitchen. This single omission is the leading cause of worktop failure in British kitchens.
• Tightening the clips one at a time to full tightness — The rim tilts, the bead squeezes out unevenly, and the sink sits slightly proud on one side. Work round them progressively.
• Relying on the foam gasket alone — Many sinks come with a self-adhesive foam or rubber strip for the rim. It is a positioning aid and it hardens with age. A silicone bead is what actually seals.

Questions people ask