How to Waterproof a Balcony

How to Waterproof a Balcony

While water is not dangerous, its accumulation and movement in between joints and spaces in a building can cause a series of problems for the building. 

From structural defects to aesthetic and functionality problems, many problems could arise when you allow water to accumulate in certain parts of a building. Hence, it is important to take considerable action to prevent water from accumulating in these building parts. 

Since the terrace or balcony is one of the parts of the building constantly exposed to water, waterproofing the balcony is integral to the building maintenance process. This becomes even more important in environments where rain, snow, and similar weather conditions are rampant. 

Hence, this article will go over the process of waterproofing a balcony while touching on important considerations before waterproofing and how to go about the waterproofing process. 

Why Balcony Waterproofing?

In June 2016, some students held a party at an apartment in Berkeley, California. During the party, the apartment balcony tore off from the building, and the bottom fell out, killing six out of the 13 people on the balcony when the accident occurred. This is one of the tragic consequences that could arise from a weakened balcony. 

Water is one of the foremost agents responsible for weakening a balcony. It seeps through cracks and spaces on the balcony and starts a degenerative process on the substrate and the material used to construct the balcony. And the best way to prevent the degeneration of the balcony due to the presence of water is by waterproofing.  

Waterproofing is the process of making a building component impervious to water penetration. It involves using an impermeable membrane between the layers that make up the balcony to prevent water from getting to the internal part of the structure. This way, water does not get to the materials, preventing the degenerative process that destroys them. 

Therefore, the answer to why balconies need waterproofing is simple. Balcony waterproofing is important to prevent cases like the Berkeley accident. It is also important to ensure that you do not spend much money on repetitive repairs on the balcony. 

What To Do Before Waterproofing the Balcony

To start with, assess the condition of the balcony before proceeding with the waterproofing process. This means that you look out for cracks and note the balcony’s slope. This step is important because it determines the extent of the waterproofing actions you must carry out. It also determines the type of waterproofing approach that you use for the balcony. 

In looking out for cracks, you start from the balcony floor. This is the first layer that you see and walk on. Thus, examining it should be very easy. Check the volumes of joints on the floor to see if they are consistent or missing. 

A floor with missing or inconsistent joint volume means lots of spaces available for water to infiltrate and destroy the balcony. The missing or inconsistent joint volume on the finish on the balcony floor leads to the next step. 

Because the floor finish now allows for water infiltration, it means that the main material used for the flooring is also unsafe. Examining the flooring material helps you understand the extent of work you need to do concerning waterproofing. It informs the decision of whether to do a full-on waterproofing job or restore an existing one. 

It is important to mention that you must fix the cracks before you can effectively waterproof the balcony. If you waterproof the balcony without fixing the cracks, it is only a matter of time before the crack affects the waterproof membrane again, rendering the waterproofing useless.

Another thing you should look out for on the balcony is the presence of efflorescence. Efflorescence is the crystallization of certain salts, and when you notice it on your roof or balcony, it is a sign that the roof or balcony is already leaking. 

Finally, you should also look out for mold. While it can be more difficult to notice mold than cracks, you should use the following signs to note the presence of mold:

  1. Damp odor
  1. Visible mold spores
  1. Damp tiles on the floor
  1. Health issues such as difficulty in breathing and worsening headaches

Steps Involved in Waterproofing a Balcony

The following are the steps involved in the balcony waterproofing process.

  1. Prepare the balcony

You need a clean and debris-free balcony to waterproof your balcony effectively. Thus, the preparation of the balcony should start with sweeping, cleaning, and removing any traces of dirt from the balcony. 

Dirt can undo all the good waterproofing work if it is not removed. The primer membrane before the waterproof membrane needs a smooth surface to sit and adhere. Anything less than this will result in a primer membrane that does not adhere properly to the surface, affecting the waterproof membrane. 

  1. Fill Up Cracks

Remember that we said to fix the cracks before waterproofing? Well, it is the next step after cleaning and ensuring that the balcony is clean and smooth. You should fill up any crack with polyurethane sealant. There are many types of polyurethane sealant that you can choose from. 

The cracks are just one of the things you need to fill up the balcony. Aside from those, you also need to fill up the joints between the walls and the floor on the balcony. No matter how small the crack or joint is, you should fill it with sealant before moving on.

Also, you will have to wait for 24 hours after the application of the sealant before adding anything else to the balcony. This duration holds for quick-drying sealant. However, if you feel the need to, you may add more sealant 6 hours after the first application. 

You may have big cracks that will take a lot of sealants. In this case, use mortar (a combination of cement and sand). You will have to wait for 24 hours to allow the mortar to dry up. 

  1. Use Layers of Primer

The next step is to apply layers of primer to the already-prepared surface. What the primer does is act as a canvas to accept the waterproof membrane that is forthcoming. The primer comes in two layers. The first layer comes after you have mixed and homogenized the primer. You can use a brush or a roller to apply the primer. 

Then, the second primer layer comes after one hour of applying the first. In total, you should allow 3 hours for the primer to dry up first before adding the waterproof layer. 

  1. Add the Waterproof Membrane

While sealants do a good job of keeping moisture out, more is required to keep water off your balcony’s construction materials completely. This is where using waterproof membranes comes in handy. There are two membranes used in this case, and they include the PVC membrane and the liquid waterproof membrane. 

The first waterproof membrane you use is the PVC/Mesh membrane. You will need to cut this membrane into strips for the joints in the balcony. You will then apply the liquid membrane to these joints before placing the strips of PVC membrane in the joints. 

After you’ve installed the strips, apply another layer of liquid waterproof membrane to the joints to keep them in place. After that, you can use a brush or roller to apply the finishing layer of the liquid waterproof membrane onto the surface of the balcony floor. 


Ensuring that your balcony is waterproof will save you from a lot of structural, aesthetic, and functionality problems. This is why you must devote time and energy to ensuring it is done correctly. While it is advisable to have a professional handle the process for you, you can also handle the waterproofing process as long as you know your way around it. 

This guide provides direct instructions on how to go about the balcony waterproofing process, saving you the cost of employing a professional and allowing you to take charge of your home’s maintenance. 

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