Sealing the worktop: four places it fails first

Grease you cannot see

A worktop joint lives or dies on the substrate, not the colour. A film of frying fat, even if you cannot see it, blocks adhesion. The bead lets go after a few months, the sink drips into the cupboard and the carcass rots with nothing dramatic on the face.

Household all-purpose cleaner often leaves another film. I use a technical cleaner, something like OTTO Cleaner T, and let it dry. It is not theatre: it is the difference between a bond and a pretence.

A long top can move millimetres with a hot pan or sun on the edge. A skinny fillet tears through the middle (cohesion). Geometry — width against depth — matters as much as the chemistry. If the hob rocks, the bead fails anyway: clamp it first.

The four zones

Around the sink: more water, more soap. Soap attacks the fungicide. Here I want decent sanitary silicone, not a leftover from the tiling.

Against the upstand or wall: different materials often meet (timber, glass, stone). More movement, more chance of a split.

Beside the hob: heat and aggressive fat. The bead fades, goes brittle or lets go first.

The end cap / edge: knocks, chairs, the supermarket of corners. Mechanical load; the flank peels.

Chemistry by the top

Natural stone or composite: OTTOSEAL S70 (or another stone silicone). Acetoxy sanitary grade stains the edge with a plasticiser halo.

Laminate, compact, general meetings: OTTOSEAL S110 often suits me, neutral, without eating the aluminium of a trim.

The hob: pick a product that will take the heat load of that install, not the cheapest tube on the shelf.

How I do it

Strip old residue fully if you are replacing.
Degrease for real and let it dry.
On a rough face (textured plaster, coarse stone), tape can keep a clean line.
Gun the bead under pressure, into the back of the meeting.
Tool with a neutral finisher. A finger in lemon washing-up liquid eats the mould protection; six months later, black dots.

What the cartridge will not fix

A hob that is not clamped. A sink already leaking at the waste, not at the joint. Closing that with more silicone is theatre: the water still finds the cupboard.