Which sealant should I use around a kitchen worktop and splashback?

A kitchen joint moves, gets hot, gets wet and gets scrubbed — which rules out most of the obvious answers and makes the substrate the deciding factor.

Difficulty: beginner
Time: 30 min
Read: 5 min
Safety: caution

Short answer

Use a neutral-cure sanitary silicone or a hybrid MS polymer along the back of a worktop and around a sink. Neutral cure is essential if the worktop is natural stone, and hybrid is the better choice if the joint will be painted or if the splashback is a material silicone struggles with. Never use decorator's caulk here — it will not survive the water.

The joint between a worktop and the wall behind it does more work than people assume. The worktop moves as the units settle and as the room heats; a laminate top expands with temperature and swells irreversibly if water gets to its core; the joint is scrubbed with hot water and detergent constantly; and the wall behind is often tile, painted plaster or a glass or acrylic splashback, each of which behaves differently.

Safety

Acetic-cure silicone etches marble, limestone and some other natural stones permanently and will corrode bare copper and brass — on any of those, use a neutral-cure or hybrid grade. Water getting behind a worktop joint into a chipboard core causes swelling that is not repairable, so a failed seal here is more expensive than it looks.

What you'll need

neutral-cure sanitary silicone or hybrid MS polymer sealant
a decent gun and a smoothing tool
isopropyl alcohol or methylated spirit
silicone residue remover, if replacing an old bead
masking tape
backer rod, for a wide gap

Step by step

Identify the worktop material first.Laminate over chipboard or MDF is the common case and the one most vulnerable to water at the joint. Solid timber moves seasonally and needs an oil-tolerant sealant. Natural stone and quartz composite must not meet acetic silicone. Each of those changes the answer.
Identify the splashback material too.Ceramic tile, painted plaster, glass, acrylic and stainless steel all bond differently. Painted plaster is the weakest — the bond is only as good as the paint's grip — and acrylic splashbacks in particular need a sealant stated as compatible, since some attack them.
Choose neutral cure as the default.It is compatible with stone, metal and most plastics, it does not smell of vinegar in a kitchen, and it costs very little more. Acetic grades are fine on tile and glass and are a permanent mistake on marble.
Choose a hybrid if the joint will be painted.Where the splashback is painted plaster and the joint sits in a run of paintwork, silicone is the wrong product because it cannot be painted. A hybrid MS polymer seals and takes paint.
Remove every trace of the old bead before resealing.Cut out the bulk with a plastic blade, then use a silicone residue remover and finish with alcohol. New silicone does not bond to old, and the invisible film is what makes a reseal lift within months.
Deal with the cause if the joint keeps opening.A worktop that is not fixed down, a unit that has settled, or a wall badly out of true will keep opening the gap. Screw the top down properly and pack the units level first — no sealant survives a joint that moves several millimetres.
Seal the cut edges of a laminate top, especially around the sink.The exposed chipboard or MDF core at a sink cut-out and at the tap holes is where water gets in and causes irreversible swelling. Seal those edges with silicone or a proprietary sealer before the sink goes in, not afterwards.
Cut the nozzle to the joint width and lay one continuous bead.Mask both sides for a crisp line, gun one pass at a steady speed, tool once with clean water or a proper solution, and pull the tape while the bead is wet.
Keep the joint dry until it has fully cured.At least twenty-four hours and longer in a cold or humid kitchen. Washing up against a half-cured bead is how a new seal starts lifting at one end.

Tips

A scribed or upstand detail — a proper upstand piece or a tiled return — removes the movement problem far better than any sealant. On a wall that is badly out of true, that is the real fix.
Match the sealant colour to the worktop rather than the wall. The eye reads the horizontal line, and a matched bead disappears.
For a solid timber worktop, oil the timber first and let it cure, then seal. Sealant applied to bare timber that is later oiled ends up with oil under its edges.
Behind a hob, the joint gets hot. Check the sealant's temperature rating, and keep any bead well clear of a gas burner or a hot plate.
The sink rim seal and the worktop-to-wall seal are two separate jobs. Doing one and not the other is the usual reason a laminate top swells at the sink.

If it doesn't work

The bead has lifted along the worktop edge

Cause: The worktop moves, or the joint was sealed over old residue — Fix: Fix the worktop down properly first, then remove the old bead completely, clean with residue remover and alcohol, and reseal.

The laminate has swollen near the sink

Cause: Water reaching the chipboard core through an unsealed cut edge — Fix: Not repairable — swollen chipboard does not come back. Reseal every cut edge and tap hole on the remaining sections to stop it spreading, and plan to replace that section.

A dull etched line on the stone along the joint

Cause: Acetic-cure silicone on natural stone — Fix: Permanent on marble and limestone; a stone restorer may improve it. Use neutral cure from now on.

The bead keeps going mouldy behind the taps

Cause: Standing water and residue in a joint that is never dried — Fix: Clean the film off weekly and dry the area after use. Check whether water is getting behind the bead, in which case it needs replacing rather than cleaning.

Questions people ask

Can I use bathroom silicone on a kitchen worktop?

A sanitary grade is the right kind of product. Check whether it is acetic or neutral cure — on natural stone, quartz or near bare copper, it must be neutral.

Can I use decorator's caulk behind a worktop?

No. It has low movement capability, it is not waterproof, and it will crack and let water into the worktop core. This is one of the clearest cases of the wrong product.

What sealant for a glass or acrylic splashback?

A neutral-cure silicone or a hybrid, and for acrylic check the manufacturer's compatibility list — some sealants craze acrylic sheet. Glass is straightforward; acrylic is not.

Should I seal under the worktop as well?

Seal the cut edges of the core, especially at the sink cut-out and tap holes, and bed the sink to the manufacturer's instructions. That is what keeps water out of the chipboard, which is the failure that cannot be repaired.