Quick Ways to Tell if Shower Waterproofing Exists

08 January 2021

When shopping around for properties, sellers frequently attempt to grab your attention by talking about how their shower is waterproof and will never leak. It sounds great - after all, when you’re buying a house, you want as little hassle as possible. The last thing you want is to have to deal with a leaking shower after you move in.

Unfortunately, determining whether a shower waterproofing membrane is fully intact can be a challenge for a layperson. It is not easy to know whether the shower contains the water flowing through it, even if you turn it on and test it yourself.

In these situations, what can you do? What would indicate that shower waterproofing isn’t working correctly or if there’s any waterproofing at all?

Indications That A Shower Or Bathroom Hasn’t Been Properly Waterproofed

It’s time to look at the telltale signs of chronic, persistent leaks. These include:

  • The shower doesn’t fit snugly in the wall: Poorly-fitting showers are often evidence of a hastily-completed job. And that usually means that the original installer didn’t take the time to fit the waterproofing membrane correctly. If there are gaps to the side of the shower or at the back, be wary.
  • There’s a musty smell in the air: If you walk into a bathroom and smell a kind of stale, odorous smell, then it is a sure sign of a leak. When water escapes the shower unit, it inevitably creates a dank smell that immediately hits you when you walk in.
  • You can see mould and mildew on the walls: Mould and mildew are the most common causes of dank and musty smells. If there is mould in the bathroom when you look around or evidence of its regular removal, that’s strongly suggestive of a shower leak.
  • The walls look warped: When moisture gets into walls, it changes the underlying material’s density, creating a warping effect that you can see from the outside.
  • The floor is soft or spongy: Bathroom floors made of a wooden truss system should feel firm underfoot. If they feel spongy, then it is a sign of a water leak.
  • Gaps between the shower unit caulk and tiles: Caulk is a special material that helps to complete shower waterproofing by preventing water from running down the gaps n the panelling. However, it can crack and disintegrate as it gets older, leading to annoying leaks.

Why is Waterproofing Important?

Shower waterproofing is essential for two main reasons: to protect your health and maintain a property’s value. When water gets into bathroom building materials, it leads to mould and mildew, which can cause health problems. It can also cause rot and other types of material degradation, necessitating expensive repair bills.

What Can Happen If There is No Waterproofing or If Waterproofing is Defective?

Most shower units should come with a plastic sheet behind the tile backer board to keep water from escaping into the wall cavity. If they don’t, or the existing waterproofing membrane sheet is defective, it can lead to various issues.

Some people wonder whether tiles and caulk are enough to prevent moisture from getting into their bathroom walls and causing damage. Under perfect conditions, they are. But remember, both tiles and caulk crack easily. And when they do, they provide no defence against water infiltration.

Other shower units use cement boards in their structure, which looks like it should keep moisture out, but, cement is a highly porous building material and soaks up water like a sponge. It will dry out quite quickly if you get it wet and won’t need any special mould treatment; however, it will still collect water which can pass through from the shower to the cavity behind.

If the shower is modular (that is, it looks like a separate unit installed independently of the rest of the bathroom), you’ll also want to check all the horizontal surfaces. Look for cracks along recessed niches, half walls, the shower floor, and benches. Even the smallest hairline crack can lead to leaks which later necessitate hefty repair bills.

Wrapping Up

Ultimately shower waterproofing membranes are a requirement. While traditional building materials, such as silicone filler and tiles, can prevent water from penetrating behind the shower, they’re not perfect. Eventually, they’ll lose their integrity and water will be able to flow unimpeded, leading to the problems we discussed above.


Ben is the Director and Licensed Building Inspector at Safeguard inspections in Brisbane’s Manly West. He has over 25 years of building industry experience and an impressive five-star Google rating.


Blog archive