Why does my balcony leak into the room below?

A balcony has every difficulty an internal wet area has, plus thermal movement, direct sun, wind-driven rain and a structural connection to the building that moves independently. That is why balcony waterproofing failures are so common and why the repairs are so often unsatisfying.

Where they leak

• The threshold at the door, where the membrane has to turn up and be dressed into the frame, and where the level difference is often too small.
• The outlet, where the membrane must be sealed into the drain rather than finishing near it.
• The perimeter, at the junction with the wall and at the edge or balustrade fixings.
• Balustrade posts fixed through the membrane after it was installed, which is a very common cause.
• Cracked or missing sealant at movement joints, which are essential on an exposed slab.

Why coatings applied over tiles rarely work

A common repair is a clear or coloured coating brushed over existing tiles and grout. It can help when the only problem is porous grout, and it does nothing when the membrane below has failed or the outlet detail is wrong. Since the coating is applied to the surface, it is also exposed to sun and traffic, so it needs recoating on a cycle.