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Why a Balcony Leaks and How to Fix It

Article Overview

This article deals with masonry balconies; concrete, tiles and grout, stone, etc.

Why is my balcony leaking?

    1. The masonry surface is porous and possibly damaged, and the waterproofing membrane has failed. This is the most common reason.
    2. There may be structural problems with the balcony, such as: lack of expansion joints, drainage problems or flashing problems.

How do I fix my leaking balcony?

There are two options, depending on your cause:

  1. Make the surface water-repellent.
    Applying Shower Plug sealer to the balcony surface makes it water-repellent, and this fixes the leak.
  2. Hire a tradesman to repair the structural problem.
    If the balcony has structural issues, a relevant tradesman will need to be consulted. You can also hire a professional tradesman to replace the tiled surface and waterproofing membrane.


Balconies are a common source of water leaks in apartments and houses.¹ There are many reasons why a balcony can leak, and a few different options to repair them. In this article, Concrete Protection Company will identify the most common balcony leak causes, their solutions, and at the end of the article discuss how Shower Plug sealer can be used to waterproof a balcony.


Balconies − overview

To properly understand what causes a masonry balcony to leak, we will briefly look at the components of a balcony.

  • The balcony plan/design
  • Structural bearers and frame made from metal or wood
  • Cladding that covers the structural frame
  • A waterproofing membrane that sits below the surface
  • The masonry surface of the balcony, such as tiles and grout, stone or concrete.
    Water generally leaks through the masonry surface of the balcony, then into the subsurface structure. Usually the membrane will stop the water at this point, preventing it flowing into the rest of the structure.

When the membrane is compromised, water will damage all the balcony’s components, but in different ways, and at different rates. The longer a leak is allowed to continue, the more damage can occur and cost to fix it. Even with a functioning membrane, the surface itself is at risk of water damage.

Shower Plug can repair and prevent this.


Balcony Water Leaks − a List of 10 Common Causes

Masonry balconies leak due to a variety of possible causes. Below is a list of the most common ones.

1. Porous masonry surface 

First and foremost, masonry materials such as tiles, grout and concrete are not waterproof. They are inherently porous and will allow water to penetrate through to the membrane.

Unless the surface is made water-repellent with a sealer, water penetrates through and then damages all elements of the structure over time. This includes damage to the membrane.

2. Broken balcony surface

Breaks in the surface like cracks in grout, tiles or concrete, are very conspicuous causes of balcony leaks. Water will pass through these cracks. The break can often be simple to patch up, using grout (see our article on how to repair grout). Once patched up, the entire surface should be sealed with Shower Plug for water-repellency. If the surface break is less than 1mm wide, this can be sealed using Shower Plug.

Broken/drummy/dislodged tiles would require the work of a tiler. Shower Plug sealer would still be important after the tiles are repaired, and tilers can apply the product as part of the repair.

3. Structural movement

Building expansion and contraction occurs when a building heats up and cools down. It also occurs when water saturates the building materials. As the building expands and contracts, it causes breaks in the structure. This occurs over the long term.

Some balconies/buildings will have expansion joints to compensate for thermal expansion.

Expansion and contraction causes breaks in the various components of the balcony, such as the surface, tiles and grout, concrete cladding, and the waterproofing membrane. In regards to leaking water, the most important breaks occur in the surface and the membrane.

The surface will break and crack in places such as the grout between tiles, between the wall and floor joints and tiles can even become dislodged or buckle, in small or large numbers. When this happens, water will leak through the broken surface and into the structure below.

The expansion and contraction process can also warp or tear the membrane.
Balconies often require expansion joints (flexible joints that allow for building movement) or it can buckle as the building moves over time.

Expansion by efflorescence

Water also causes expansion and contraction of masonry substrates through a process called efflorescence.

In short, efflorescence is the white crystalline streaks that often form on exposed masonry surfaces. They are formed when water saturates a masonry surface and dissolves the salts and minerals contained in the masonry. As water then moves through the masonry it takes the salt and minerals with it. When the water evaporates, the salts and minerals are left behind as white crystals or streaks. This can form on the surface, but these crystals can also accumulate within the surface. When the minerals crystallise there, they expand, splitting the masonry apart, causing cracks. The cracks increase the ability of leaking water to pass through the masonry.

If you are seeing efflorescence on the surface of your masonry, this can indicate the cause of your balcony leak is the porous masonry itself. The masonry should be cleaned and then sealed with Shower Plug to prevent further efflorescence and leaks.

4. Balcony membrane failure

The waterproofing membrane is a waterproof sheet that lies underneath the surface, preventing water from soaking through the structure. They are commonly made from polymers, bitumen, rubber and/or other materials. Membranes commonly have a service life of 5-10 years after installation. Required by the building code in Australia, they are a necessary measure for waterproofing balconies.


Video depicting membrane failure:

Membranes can fail for many reasons:

  • Poor quality membrane.
  • Poor workmanship.

The leading cause of membrane failures is errors made in workmanship.

Membranes are often complicated, labour-intensive and demanding pieces of technology. They require professionalism in knowledge, discipline and teamwork both within the application team and with other construction teams on-site, in order to be properly installed and coordinated. They can fail for many reasons associated with workmanship:

  • Membrane not given enough time to cure
  • Surface not cleaned and dried or otherwise prepared or primed
  • Inconsistent adhesion to the surface
  • Air trapped beneath membrane
  • Membrane walked on/contacted before it’s cured
  • Pressure placed on membrane
  • Overlaps between membrane not fully sealed
  • Incorrect installation of other elements of the balcony
  • Cost cutting.
  • Membranes can be damaged through building modifications during the building’s lifespan.

Improper use

  • E.g. indoor membrane used outside
  • Cost cutting

Wear and tear

  • Building movement
  • Interference from building work/renovations later

Age of membrane

  • Membranes deteriorate through usage, exposure to water and time
  • If mould has developed on the membrane over its lifespan, this will cause damage
  • If water has consistently pooled up on the membrane over its lifespan, this will cause damage

Poor condition of surface below membrane

  • Contaminated
  • Uneven
  • Unsuitable for primer

Generally, this is difficult to identify without training and equipment, but if the surface is porous and/or damaged, membrane failure is likely to be a reason why the balcony is leaking.

Membranes can be replaced by removing the tiles and replacing the membrane. The surface can be waterproofed by using a penetrating sealer instead, leaving the membrane redundant.

5. Pooling of water on balcony

Continual pooling up of water in the area, due to bad drainage or lack of sufficient fall, can lead to increased water pressure on the balcony and increase chances, or rates, of water leaks.

This is easy to identify and may require specialist help to fix.

6. Weather damage to balcony

Rain, heat, cold, UV-light, ocean-air salt and other forces all wear away at the integrity and certain parts of balconies.

7. Bad drainage on balcony

  • Drain outlets − too few or too small in diameter
  • Improperly placed
  • Insufficient fall to outlet
  • Blocked drains
  • Lack of preparation for waste or debris

This will often lead to pooling as above.

8. No provisions for water overflows on balcony

In the event that there is a problem with drainage or heavy rainfall, there should be provisions for water to exit.

9. Inadequate flashing 

Flashing is thin pieces of material installed to prevent the passage of water through vertical/horizontal joints, including the balcony floor and wall or the window/door opening.

This is a fairly noticeable problem; inspect the flashing for issues. It will need to be repaired professionally.

10. Inadequate expansion joints 

If the balcony is buckling or breaking and there is no expansion joint, this could be a cause of your leak.

How to Fix a Leaking Balcony

What does it cost to repair a leaking balcony?

There are three options, from lowest to highest cost:

  1. Shower Plug the surface and make it water-repellent. Minimum: $52.50 for 7m². See the prices here.
  2. Remove and replace the membrane, along with the tiles. Contact a waterproofing tradesman. Prices are in the thousands of dollars.
  3. If the balcony has a structural issue, contact a suitable tradesman. Price will depend on the job required.

The all-round most efficient way to fix a leaking balcony

To prevent water leaking through the surface of the balcony, for most issues, we recommend applying Shower Plug masonry sealer.

Shower Plug is a liquid sealant that soaks into masonry surfaces and renders them water-repellent. It is a leading balcony sealing product, tested and appraised by Australian universities and the CSIRO.

Once treated with Shower Plug, the surface itself is the sealed barrier against water. No water can penetrate through. No membrane replacement is required. It is simple enough for DIY users to apply and is ready within 12 hours. Therefore, it is the most efficient way to fix a leaking balcony.

Shower Plug is applied in two coats, using a brush, roller or spray. It is then wiped off after the second coat, leaving no changes to the surface appearance or texture. The surface remains cosmetically identical to its original state, but it has become chemically waterproof.

The reasons why we recommend this method:

  • Through its design and advanced chemistry, Shower Plug is the most cost-effective method to repair a leaking balcony.
  • The tiles and membrane replacement process is the main cost associated with balcony leak repairs. By applying Shower Plug sealer, you can waterproof the balcony without removing the tiles, and bypass the main cost of leaking balcony repair.
  • The application method and equipment is simple enough to be a DIY task.
  • Porosity/permeability of the surface is the root cause of most balcony leaks. Shower Plug treats this. Membranes do not.
  • The surface is protected from all forms of water damage.
  • Shower Plug’s waterproofing effects last for a minimum of 10 years.
  • Shower Plug has proven effective over 30 years on the market, and in laboratory testing by major university and industry bodies in Australia. This includes the CSIRO, University of New South Wales and Victoria University who have appraised the product.
  • Shower Plug is made in Australia to the highest standards.

Questions about balcony waterproofing:

  • Do balconies need to be waterproofed? Yes, for two reasons: firstly, the Building Code requires a membrane, and secondly, the surface needs to be waterproofed as well, or it will be damaged by repeated water exposure. Shower Plug is the system that will do this.
  • How long should waterproofing last? Membranes will on average last 5 years. Shower Plug will last minimum 10 years and can be reapplied at any time.

What to consider when using Shower Plug to treat balcony leaks:

  • Shower Plug will solve many cases of balcony leaks that involve water passing through the surface, however items 6-10 in the list above will require consultation with CPC staff to determine if Shower Plug can assist.
  • Shower Plug will only bind to masonry substrates. It will not bind to plastics, metal, timber, silicone, etc. Coatings over the tiles will prevent Shower Plug adhering.
  • Shower Plug will seal gaps of up to 1mm wide. Gaps in the surface greater than that width need to be patched up with grout.
  • Shower Plug will repel up to 10cm depth of water.

Find out more about Shower Plug, here.

Other ways to fix a leaking balcony

Membrane replacement is an option. A professional waterproofer, and/or builder or tiler will need to be contacted if that method is considered.

If the issue involves expansion joints, falls, drainage, flashing or other structural issues, a tradesman is required.

In both these cases, it is still useful to waterproof the balcony surface with Shower Plug once the main cause is fixed. This will ensure full balcony waterproofing is achieved.


With this information, you have a starting point to understand and fix your balcony leak.

If further information is required, Concrete Protection Company is available for consultation. Email

To learn more about Shower Plug, see this page.

To purchase Shower Plug, see this page.

Concrete Protection Company
Concrete Protection Company
Concrete Protection Company (CPC) is an Australian-owned and operated company which specialises in high-quality solutions in masonry protection. Our objective is to offer high-quality, reliable, long-lasting and easy to use products to help maintain your masonry surfaces.

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