How to tell if your waterproofing has failed

Step by step

1. Look at the room below or next door

   Bubbling paint, a soft patch of plaster, a stain on the ceiling below, or skirting board lifting in the adjoining room. Water travels — the damage often shows up somewhere other than the bathroom.

2. Press on the floor and the shower base

   Any softness, flex or hollow sound under the tiles means water has got into the substrate. Tiles should feel completely solid underfoot.

3. Tap around the walls

   Tap gently across the tiled wall with a knuckle. A change from a solid sound to a hollow drummy one means the tile has debonded — usually because the sheeting behind it is wet.

4. Look at where grout keeps cracking

   Grout that cracks in the same joint repeatedly, especially at the floor-to-wall junction, is movement. Movement means the substrate is unstable, which usually means it is wet.

5. Check the smell

   A persistent musty smell that cleaning does not fix, particularly noticeable when the room has been closed up, means moisture is sitting somewhere it cannot dry out.

6. Watch the shower screen and the door frame

   Silicone that will not stay stuck, a screen that has moved, or a swollen timber door frame at floor level all point the same way.

Common mistakes

• Regrouting repeatedly instead of investigating why it keeps cracking
• Assuming a ceiling stain below is a one-off
• Sealing over the symptoms with silicone
• Waiting until it is visible from the room below — by then the subfloor is usually affected