How to Waterproof North-Facing Exterior Walls?

It may not seem intuitive at first, but moisture can penetrate the masonry that makes up your outer walls to affect the inner walls of your home.

Over time, exterior walls exposed to rain and humidity can seep through the bricks until they reach the wood and drywall of the interior.

In incredibly humid places like the southeastern part of the US, exterior walls (especially the north-facing ones) that take longer to dry out will present danger of moisture damage along with mold or mildew for the interiors as well.

To prevent such damage to the interior of your home, you will need to use waterproofing paint for exterior walls, following the proper steps.

Steps to Waterproof Your North-Facing Exterior Walls

Plastering the walls is a traditional way to protect your home exteriors.

It’s a reliable product that not only protects the north-facing exterior walls from moisture but also improves the aesthetic value.

But the plaster is often not enough in many cases, which is why you will need to waterproof the walls nicely.

To start with the waterproofing process of your vulnerable north-facing exterior walls, you can follow these steps…

Step 1 – Inspection

The first step is to conduct an inspection of the exterior walls to find any faults. This means you are looking for obvious sources of moisture penetration or creation.

From cracks in the bricks to condensation forming inside the walls to a pipe leaking, addressing the faults first will prevent moisture damage even after you waterproof the exterior.

Once that is completed, you are ready for the next step.

Step 2 – Gutter Cleaning

Gutters that are clogged not only cause the water to flow down the exterior walls, but they also retain water that may be absorbed by the roof or fascia boards of the home.

By cleaning your gutters at least twice a year, you can prevent water buildup that may add to the damage being created. This also helps control the growth of mold.

Step 3 – Choose the Right Waterproofing Product

Different waterproofing products for walls are made of different materials.

To properly seal an exterior wall, choose a waterproofing coating that matches the material.

For brick and concrete, for example, using a concrete waterproof paint coating will do the job. Or you can use a silicate-based concrete sealer, which will create a waterproof coating on the surface of bricks and concrete.

However, this type of sealer can only be used on walls that are not painted or previously sealed.

If you want to paint the walls, waterproof paint similar to acrylic will work nicely. You must select the right breathable formula to allow any moisture trapped under the paint to dry out.

This type of paint can also be used on outside walls that have been painted.

Step 4 – Prepare the Walls for Waterproofing

Whatever product you choose, it is crucial to repair any damage to the surface of the walls first.

Be sure to select a good quality filler made to be used on outdoor walls. Poly caulks, for example, are very strong and durable, ideal for high-traffic or exterior applications.

Apply it firmly into the damaged area, feather the edges with a scraper for a flush finish, and let it dry as per the manufacturer’s curing time.

Once you add the filler, let it dry before grinding or sanding it smooth, and then remove any dust.

In addition, adding a waterproofing additive to the wall plaster can be most helpful if you are considering wall plaster. This will help eliminate moisture from penetrating the exterior wall when added to the plaster.

After you are done, let it fully dry before you apply the waterproof coating to the walls.

Step 5 – Apply the Waterproofing Product

You can use a brush or roller to apply the waterproofing agent, depending on the texture of your wall and the product you’re using.

Work the coating into all the nooks, hairline gaps, and surface undulations—north-facing walls often have tiny imperfections that love to trap moisture.

In most cases, you’ll need to apply at least two coats for proper protection.

Allow the first coat to dry completely (follow the manufacturer’s recommended drying time) before adding the second. This ensures the membrane forms a continuous, pinhole-free barrier.

It’s always better to be safe than sorry when it comes to waterproofing, so a second coat isn’t just “optional”—it’s smart insurance against future seepage, paint peeling, and damp patches.

Use a third coat if the wall has a history of moisture issues or if the surface is highly porous.

Step 6 – Test and Reapply When Needed

If you want to know whether the waterproof coating will actually protect the exterior walls, you will need to conduct a proper test.

Let a few days pass before conducting the test so that you know the coating is fully dry and hardened.

Spray a water hose with the nozzle at a 30-degree angle around the walls of your home. Spray plenty of it, which may take several minutes, up to an hour or longer.

Once completed, use a moisture meter to see if any moisture is present. If not, then the waterproofing worked.

If the meter detects moisture, you must address the issue and reapply the waterproofing coat on the outside walls.

Also, after the recommended longevity time has passed, you can add another application over time to maintain the waterproofing qualities of exterior walls.

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Why are North-Facing Outdoor Walls Vulnerable?

North-facing walls look innocent, but they quietly take the worst beating from moisture.

Unlike south-facing walls that enjoy direct sunlight for most of the day, north-facing surfaces often remain in the shade. That means they stay cooler and retain moisture for much longer after rain, fog, or winter dew.

When a wall stays damp, it becomes a perfect environment for seepage, efflorescence, algae growth, and long-term structural deterioration.

Because these walls dry slowly, tiny cracks can turn into moisture highways, pulling water deeper into the plaster and even the masonry.

Over time, the trapped moisture weakens paint films, causes bubbling, and accelerates freeze–thaw damage in colder regions. Waterproofing acts as a protective skin—blocking water intrusion while allowing trapped moisture inside the wall to breathe out.

Key reasons why north-facing walls are particularly vulnerable:

Minimal Sun Exposure: Without direct UV heat, water on the surface evaporates slowly. Dampness lingers for hours or even days.

Higher Moisture Retention: North-facing surfaces tend to remain cooler. Cool substrates absorb moisture faster and release it more slowly, increasing the risk of damp patches.

Favorable Conditions for Microbial Growth: Algae, mold, and mildew thrive in low-light, moist areas—exactly what a north-facing wall offers.

Increased Risk of Efflorescence: Persistent dampness dissolves salts inside the wall and brings them to the surface, leaving that white, powdery residue.

More Vulnerable During Monsoons/Wet Seasons: With slow drying, even light rain creates compounding moisture buildup, making seepage more likely.

Problems if You Don’t Waterproof the House from the Outside

From the damage caused by the moisture itself to lichen and algae on the brickwork to mold or mildew forming inside the walls, there are many things that might cause damage to the exterior and interior of your home.

If you live in a dry climate, the waterproofing will be that extra safeguard that will last for a long time.

However, if you live in a moist, humid climate, you may experience the following issues if you do not waterproof the exterior of your home.

1- Cracks

Water that manages to get inside the brick or mortar can freeze and then expand to cause cracks, which let additional moisture inside.

Called ‘spalling,’ this can also lead to mold and mildew growing inside the cracks, which can cause further damage.

2- Dampness

Interior walls may become damp from exposure to the excess moisture that has penetrated from the outside.

This means that the material itself can become damaged from moisture, which will need to be addressed.

Plus, the dampness is a magnet for mold and mildew, which may consume the organic materials and cause extensive damage.

3- Efflorescence

If you see unexplained white patches on the brick, this is known as efflorescence. This is a condition caused by damp patches that contain salts.

If they seep out to the surface of the brick, they can cause ugly white patches that are difficult to remove. Plus, if they make their way into the plaster, they can damage it from the inside.

Finally, the resale value of your home can be considerably reduced with the presence of mold, mildew, and white damp patches. These not only make the home look unattractive, but also cause damage that can be expensive to repair.

However, the good part is that if you address the problem early with the right combination of surface preparation, crack sealing, high-quality waterproof coatings (like those offered by Sherwin Williams), and proper drainage can significantly extend the life of the wall.

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How Effective are Hydrophobic Coatings in Waterproofing Exterior Walls?

If you decide to paint the brick or concrete instead of using a sealant, then choosing a super hydrophobic paint coating can be of great service.

This type of waterproofing paint for exterior walls actively repels water and comes in a range of qualities that can match your needs.

Hydrophobic paint can also be used on other materials made from minerals, such as roof tiling or on your terrace floor.

The coating will still penetrate the surface and provide ample protection from moisture.

In addition, they can help add to the thermal insulation of the brick and may last as long as two decades before you need to apply additional coats.

For application, you can also choose a clear coating called masonry crème that lets the original color of the brick still be seen on the outside.

Façade Coating

A façade coating will cover the brick and add color to the external walls, providing a waterproof layer that will last for at least a decade or more.

This type of water-resistant paint is breathable, which is good as it allows any moisture that penetrates to dry out. To achieve a smooth finish and help conceal any inconsistencies in the brick’s color, you will need to apply two coats.

In addition to roof tiles, they can be used on any surface made from minerals, resisting the water and any dirt or grime that might wind up on the surface.

Besides the above, there is also Acrolein Elasticized Paint that can be used for waterproofing concrete surfaces, including walls outside. You can choose from a range of colors that work quite well on brick and stone as well.

Related FAQs

What can you use to waterproof your exterior walls?

Exterior walls can be waterproofed using cementitious waterproof coatings, elastomeric or acrylic waterproof paints, and silicone- or polyurethane-based sealants.

For cracks and joints, polymer-modified fillers and PU sealants work well. Water-repellent solutions like silane–siloxane penetrants are useful for brick and stone surfaces, as they block water while allowing the wall to breathe.

Proper surface preparation, priming, and drainage improvements are essential for long-lasting results.

How to waterproof existing paint on the outside wall of the house?

Start by cleaning the wall thoroughly to remove dust, algae, and loose paint. Repair cracks, damaged plaster, and joints using waterproof fillers or crack sealers.

Lightly sand glossy or peeling areas to improve adhesion. Apply a compatible waterproof primer, followed by two coats of elastomeric or acrylic waterproof paint over the existing surface.

Ensure proper curing time and apply during dry weather for best performance.

What problems could occur if you fail to weatherproof the external walls of your home?

Without weatherproofing, exterior walls can absorb moisture, leading to damp patches, mold growth, and peeling paint.

Over time, water seepage can weaken plaster, corrode reinforcement, and cause structural damage. Internally, it may result in musty odors, poor indoor air quality, and higher maintenance costs.

In colder regions, trapped moisture can also cause cracks due to expansion, reducing the building’s lifespan.

The Bottom Line

Waterproofing north-facing exterior walls is not just a preventive measure—it’s a long-term investment in your home’s durability and comfort. Equally important is regular inspection and maintenance, especially after monsoons or prolonged wet weather, to catch minor issues before they escalate.

Choosing breathable, weather-resistant materials ensures trapped moisture can escape while preventing water ingress.

In the long run, a well-waterproofed north-facing wall not only protects the building structure but also improves indoor air quality, enhances energy efficiency, and reduces costly repairs. Thoughtful planning and correct application today can save years of trouble and expense later.