A hollow or ragged joint: the finger and the washing-up liquid

What you are looking at

A shower joint done properly is flat or slightly to fall. Water leaves. A hollow joint — the crescent of a finger — holds soap and moisture. The edges go to a film: they fray, lift, and the middle is too thin to stretch.

That is not a cosmetic niggle. It is geometry: no body in the centre, skins on the flanks.

Washing-up liquid is not a finisher

Washing-up liquid is made to break grease. If the suds creep between fresh sealant and the tile, they cut adhesion. A soap film stays. Acids, dyes and perfume eat the fungicides. Months later: yellowing or black specks, “for no reason”.

If you have no smoothing agent, clean tap water is less harmful than the sink. On natural stone, never washing-up liquid: it stains the edge.

How to tool with body

Dry, soap-free substrate. Push the silicone into the joint, a little overfull, no bubbles. A light mist of pH-neutral finisher — not a puddle that runs underneath. Spatula (wood or plastic) about 2 mm wider than the joint, one pass. I use Fugenfux when I want a controlled radius and angle.

A triangular or flat section puts mass in the middle. A round finger steals it to the sides and leaves a channel.

Do not tool with spit. Your mouth is full of bacteria; you plant them in the mass.

The usual mistakes

Too much soap: liquid slides under the bead before it grabs. Touching it again and again: the skin forms and wrinkles. Tape on a shower edge: a little step where water sits. Better freehand, so the meeting almost disappears.

If the joint is already a deep gutter full of dirt, do not shoot over it. Replace.

Why flat drains

On a flat face the droplet runs. In a concave radius it hangs by capillary action. Less still water, less mould. And there is body for cohesion when the building moves.

Exceptions

A skin already lifting at the edges almost never trims back to a sound joint. Cut it out and redo. On stone, stone chemistry and a stone-safe finisher, not the washing-up trick.