How to Seal Brick Safely: Breathable Sealers vs Film Coatings (What to Choose)

Breathable sealers penetrate the brick surface and allow moisture in vapor form to escape. Film-forming sealers create a surface layer that blocks some moisture movement. Each type trades off ventilation, stain resistance, and appearance differently.

Key decision factors include substrate type, environment, maintenance goals, and anticipated use. Choose breathable options when moisture management is a priority; opt for film coatings when a strong surface barrier and color enhancement are desired. Always verify prep needs, compatibility, and follow-up maintenance in the product instructions and labeling.

Fast decision scenarios

Here are a few common scenarios that can help guide your decision on which sealer type to choose:

Historic or Heritage Brick: If you’re working with historic or heritage brick, it’s best to lean towards breathable sealers. These will help preserve the natural look and character of the brick while still providing protection against water intrusion.

Driveway or Walkway: For high-traffic areas like driveways or walkways, film-forming sealers are typically the better choice. They offer excellent durability and stain resistance, making them well-suited for these demanding environments.

Pool Coping or Outdoor Kitchen: In areas exposed to salt, chemicals, or frequent cleaning (like pool coping or outdoor kitchens), film-forming sealers can provide the necessary protection against staining. However, ensure proper ventilation and moisture management to prevent trapped moisture issues.

Back to top ↑

Brick is porous and interacts with moisture through capillary rise, lateral movement, and vapor diffusion. Understanding these paths helps explain why breathable options matter. Non-breathable coatings can trap moisture and worsen damage over time.

Breathable sealers permit evaporation while film coatings tend to confine moisture. Look for signs like damp interiors, efflorescence, or spalling to gauge whether breathability is appropriate. Refer to product guides for specific brick compatibility and testing tips.

Brick porosity and moisture risks

Clay bricks are porous, meaning they’re full of tiny holes. This lets moisture move through them in three ways:

Capillary rise: Moisture from the ground seeps up into the brick like a wick.

Lateral movement: Water can spread sideways within the brick, especially when it’s wet.

Vapor diffusion: Even when bricks are dry, water vapor can pass through them and condense on cooler surfaces.

When non-breathable coatings cause harm

Film-forming coatings seal the brick’s surface tight. This traps moisture inside, leading to problems:

Blistering: Trapped water causes paint or coating to peel and bubble.

Efflorescence: Salt deposits form on the surface as trapped moisture evaporates, leaving a white, chalky residue.

Freeze-thaw damage: When water inside the brick freezes and expands, it can crack or spall the masonry. This is why non-breathable coatings are best avoided in cold climates.

Back to top ↑

Penetrating sealers differ from films by allowing water vapor to pass through the brick. This helps manage moisture and supports brick longevity. Breathable sealers are typically chosen to preserve a natural look while reducing staining potential.

Chemical families include silanes, siloxanes, silicates, and blends. Each family offers a mix of surface repellency, vapor permeability, and durability. Plan for proper prep, expected depth of penetration, and how porosity affects performance.

Performance characteristics

Breathable sealers work by penetrating into the brick’s pores, reacting with the masonry to form a protective barrier. Here’s what they do:

Water Repellency: They repel water from the surface while still allowing moisture trapped inside the brick to escape.

Vapor Permeability: This breathability prevents moisture buildup, which can lead to efflorescence and damage over time. It’s crucial for brick longevity.

UV and Freeze-Thaw Resistance: They protect against UV degradation and help prevent damage from freeze-thaw cycles, ensuring long-term durability.

Limitations and compatibility

While breathable sealers are great, they’re not perfect. Here’s when they might not work as expected:

Sealers may struggle on very dense or coated surfaces where penetration is limited. Always test a small area first.

Compatibility with Lime-based Mortars: Some sealers can react with lime in mortars, causing discoloration or damage. Check compatibility before use.

Regularly inspect your brickwork after sealing to ensure the sealer is performing as expected and no issues have arisen over time.

Back to top ↑

Film-forming sealers create a continuous outer layer on brick surfaces. Common types include acrylics, urethanes, and epoxies. They can change appearance with gloss and color, and they provide surface-level protection.

Film formers carry risks like moisture entrapment around the barrier and potential effects on mortar integrity. Prepare the surface thoroughly, follow coat thickness guidance, and consider future restoration needs before choosing this option.

Aesthetic and protective benefits

Film-forming sealers create a continuous outer layer on brick surfaces, altering their appearance and enhancing protection. They come in various types:

Acrylics offer matte to semi-gloss finishes, urethanes provide high gloss, and epoxies have a tough, durable finish. Expect some color enhancement and increased stain resistance.

These sealers harden the surface, making it more resistant to water penetration and physical impact. However, they can slightly alter the natural texture of the brick.

Risks and failure modes

While film-forming sealers offer protection, they also pose risks if not applied correctly. Moisture can become trapped within the brick, leading to:

Efflorescence: a white, powdery deposit that forms when moisture meets unsealed areas. Spalling or peeling may occur if moisture buildup causes bricks to delaminate or mortar to weaken.

Film coatings should be avoided on historic or porous bricks, and in areas with high humidity or frequent temperature changes. Always ensure proper surface preparation and substrate compatibility to minimize risks.

Back to top ↑

Define the sealing objective and how breathability will influence results. Proper prep sets the stage for long-term performance. Skipping steps invites premature wear or uneven appearance.

Moisture testing, efflorescence removal, and existing coating checks are essential. Document findings and plan patch testing to validate adhesion and performance. Use the results to decide breathable versus film options and sequencing.

Compatibility and small test patch

Before sealing your entire brick surface, it’s crucial to test your chosen sealer on a small, inconspicuous area. This helps ensure compatibility and allows you to observe the results over time.

First, select an area that’s representative of your project – same exposure, age, and condition. Then, apply the sealer according to the manufacturer’s instructions. Use a sprayer or paintbrush for even application.

Next, wait 48-72 hours to observe the results. Look for any signs of poor adhesion, discoloration, or other issues. Also, check product datasheets for specific observation periods and guidelines.

Remember: If you’re unsure about compatibility or have concerns about your bricks’ condition, consult a professional before proceeding with full-scale sealing.

Back to top ↑

Prepare with parallel workflows for breathable and film coatings, focusing