Leak in the bathroom? Sealant joints, grout or pipes

Signs of a leak in the bathroom

• A damp patch or brown ring on the ceiling under the bathroom (see damp patch on the ceiling).
• Discoloured, black or loose sealant joints and grout.
• Tiles that sound hollow or come loose, especially at the bottom of the shower wall.
• A musty smell, mould on the wall on the other side of the bathroom or peeling paint in the hallway.
• Moisture around the toilet, the washbasin or the bath.

The five most common causes

1. Sealant joints

Sealant closes the joints between wall and floor, around the shower tray or bath, and at the washbasin. Sealant is flexible, but ages: it becomes hard, comes loose or cracks. Water then seeps behind it with every shower. This is one of the most common causes of leaks in the shower.

2. Joints and tiles

Cement grout is not completely watertight; the waterproofing must come from the layer underneath. If the grout lines are cracked, worn out or there is no proper waterproof layer under the tiles, the water penetrates the wall or floor.

3. The drain

A shower drain or linear drain that is not properly connected to the floor or the drain pipe lets water run down the outside. That's a tricky one, because you can't see it. Read about recognising leaks from the shower drain.

4. Pipes in the wall or floor

The supply pipes to the shower tap, the bath and the washbasin are often concealed. A leaking coupling or a damaged pipe also leaks when no one is showering. This is the type of leak that you see as a damp patch that keeps growing.

5. Taps, trap and toilet connection

A leaking coupling under the washbasin, a loose trap or a WC connection that doesn't seal properly: often small leaks, but they can go unnoticed for a long time.

How to find the cause: step-by-step plan

1. Do the water meter test. Make sure no water is being used anywhere, note the water meter reading and check again after an hour (or overnight). If the meter continues to run, there's a leak somewhere in a pressurised pipe. If the meter is still, the leak is probably in the drain, sealant or grout: it only leaks when water is being used.
2. Test component by component. Use only the washbasin for a few days, then test the shower. First spray only on the floor near the drain, then against the walls. Note when the damp patch grows.
3. Check the sealant joints. Press a finger on the sealant: if it comes loose, is there black mould behind it or do you see gaps? Then the sealant needs replacing.
4. Look under the washbasin and behind the toilet with a torch, running a dry tissue along the connections.
5. Take photos of the damp patch with the date, so you can see if it's growing. That also helps for the insurance.

Replacing sealant joints yourself

Replacing old sealant is a job you can do yourself. Remove the old sealant completely with a sealant knife, clean the joint and degrease it, and let it dry thoroughly. Use a bathroom sealant with anti-mould properties, apply an even bead and finish it off. Let the sealant cure before showering again; the packaging states how long. Applying sealant over old sealant doesn't work: the new layer won't adhere properly.

When is it more than sealant?

If the water meter keeps running, tiles keep coming loose or the damp patch grows even when the shower hasn't been used for a few days, the leak is probably in a pipe or under the tiles. In that case it makes sense to have the source traced before any breaking starts. With leak detection we find the spot without breaking open the entire bathroom.

Safety: if water comes near sockets, lighting or an electric towel radiator, turn off the circuit in the meter cupboard.