Sealing Brick the Safe Way: Breathable Sealers vs Films—and When to Skip Both

Sealing brick aims to control water ingress and manage stains while preserving the wall’s breathability. It helps reduce weathering and makes cleaning easier over time. You should clearly define what you expect from a sealant before starting the work.

Be aware that sealing can also affect appearance, texture, or moisture handling if misapplied. Confirm the objectives you want to achieve, and check the product label and manufacturer instructions for cautions about risks like trapped moisture or sheen changes.

Benefits of controlled water repellency

Sealing brick with the right product can keep liquids out, slowing down deterioration. But it’s crucial to let moisture vapor escape. This balance prevents damage from absorbed water.

Properly sealed bricks resist stains and efflorescence. They stay cleaner longer, reducing maintenance needs.

Controlled water repellency also helps preserve the brick’s natural look. It doesn’t alter appearance like some heavy-duty sealers can.

Risks of inappropriate sealing

Using impermeable products to seal bricks traps moisture inside. This leads to hidden damage, like crumbling mortar and spalling (flaking) brick surfaces.

Trapped moisture encourages mold growth and weakens the structure over time. It can even cause cracks in walls.

Inappropriate sealing can also speed up the aging process of bricks. They may look older than their years, ruining your home’s curb appeal.

Clarifying goals before choosing a product

Before you seal, decide what you want to achieve. Are you trying to preserve the bricks’ lifespan, waterproof them, improve aesthetics, or just protect them temporarily?

Each goal requires a different type of sealer. For instance, preservation needs a breathable sealer that lets moisture out but keeps liquids away.

Understanding your goals helps you pick the right product for the job. It also sets realistic expectations about what sealing can and can’t do for your bricks.

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Masonry deterioration often starts with moisture movement through the wall assembly. Liquid transport and vapor diffusion can carry salts and minerals to the surface. Understanding these mechanisms helps pinpoint where a problem originates.

Biological growth and salt deposition can worsen staining and surface damage. Look for patterns that indicate moisture pathways and verify any diagnosis with simple checks and local guidance before choosing a treatment.

Moisture entry pathways and sources

Water finds its way into brick assemblies through various routes. The most common are:

Capillary rise: Moisture travels up from the ground, like a wick.

Leaks: Water can enter through cracks or gaps in the masonry, often due to poor installation or damage.

Flashing failures: Inadequate or damaged flashing around windows, doors, and other openings allows water to seep behind cladding and into walls.

Ground contact: When brick is in direct contact with the ground, moisture can wick up and enter the assembly.

Salt migration and efflorescence

Soluble salts present in mortar, grout, or bricks move with moisture through capillary action. When this moisture evaporates at the surface, it leaves behind salt crystals, a process known as efflorescence.

Efflorescence appears as white deposits on the brick face. While it’s often harmless, it can indicate more serious issues like waterproofing failures or poor drainage.

Internal stress: As salts crystallize within the masonry, they cause internal pressure that can lead to cracking and deterioration over time.

Freeze-thaw cycles and spalling

In cold climates, moisture trapped within brick assemblies can freeze and expand. When it thaws, the water contracts, creating cracks and weakening the masonry.

Over time, these freeze-thaw cycles cause pieces of brick to break off, a process called spalling. Spalling exposes fresh, porous surfaces that absorb even more water, accelerating deterioration.

Preventive measures: Proper drainage, adequate air circulation, and appropriate sealers can help minimize damage from freeze-thaw cycles.

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Penetrating breathable repellents seal the surface while allowing vapor to move through the wall. Silicate treatments chemically alter the masonry to reduce water intake without forming a film. These are commonly used where moisture movement matters.

Acrylics and elastomeric films form a surface layer that can block evaporation. They may alter texture and trap moisture if not compatible with the brick. Review the product data sheet and label to understand how they behave on your brick.

Breathable/Penetrating Repellents

These sealers work by penetrating the pores of your brick, creating a barrier that repels liquid water. But here’s the key: they allow water vapor to pass through, letting your masonry breathe.

How? They form a molecular bond with the brick itself, not just sitting on top like some sealers do. This makes them ideal for above-grade masonry where you want protection from rain and snow, but also need to let moisture escape.

Think of it like your skin. You want to keep sweat in (to stay hydrated) but let excess water out (to prevent sweaty palms). That’s what these sealers do for your brick.

Non-Breathable Films and Coatings

These sealers form a continuous, impermeable layer on the surface of your masonry. They work great at keeping water out, but that’s where the problem starts.

Why? Because they don’t let moisture escape. Imagine painting your skin with a thick, waterproof layer. You’d sweat, and then you’d have a big problem – trapped moisture leading to all sorts of issues. The same goes for your brick. Trapped moisture can lead to efflorescence (those white salt deposits), spalling (flaking or chipping of the surface), and even structural damage over time.

So, while these sealers might seem like a good idea at first, they often cause more harm than good on moisture-prone masonry. They’re usually best reserved for below-grade applications where water intrusion is a bigger concern than trapped moisture.

Paints, Colored Coatings, and Sacrificial Coatings

These are decorative in nature, designed to change the appearance of your masonry. They can provide some protection, but that’s usually not their primary function.

What about maintenance? Paints and colored coatings typically need periodic touch-ups or repainting. This is because they’re exposed to the elements just like your brick. And while they might protect your masonry from minor water intrusion, they can also trap moisture if they start to peel or crack.

Sacrificial coatings are a bit different. They’re designed to wear away over time, protecting your masonry until they need to be reapplied. But even these have their limitations and aren’t suitable for all applications.

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Choose breathable options when the masonry needs ongoing evaporation, especially in historic or porous assemblies. If you want to limit interior dampness while preserving some moisture transfer, a breathable product may be appropriate.

Consider the exposure, condition of the brick, and prior repairs. Verify the suitability with manufacturer guidelines and local codes, and assess whether vapor permeability aligns with your goals and the building’s needs.

Assessing porosity and existing moisture

Before you seal, check if your brick is dry and porous enough for a penetrating product. Here’s how:

Dry test: Press a piece of tissue to the surface. If it sticks, the brick is likely dry.

Wet test: Spray water on the brick. If it beads up and doesn’t soak in, your brick might be too dense for penetration.

If your brick is wet or compromised, defer sealing until it’s dry to prevent trapping moisture.

Preservation and historic masonry criteria

Breathable treatments are usually best for historic or original brick. Here’s why:

They maintain vapor transfer, allowing moisture to escape naturally.

They preserve the appearance of the brick, unlike films that can alter its look.

For historic preservation, stick with products designed for old masonry and follow local guidelines.

Climate and exposure considerations

Your climate plays a big role in choosing a sealer:

In humid, rainy climates, breathable approaches help prevent moisture buildup behind the brick.

In freeze-prone areas, breathable sealers can help reduce freeze-thaw damage by allowing water to escape.

Always check your local conditions and follow manufacturer guidelines for best results.

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Non-breathable films can be useful for cosmetic uniformity or temporary protection during construction. They may also be used with drainage-focused assemblies where moisture is managed by design. Understand these limitations before proceeding.

Be aware that films can trap moisture and may require removal or replacement over time. Always weigh the trade-offs and consult the product instructions or a professional if uncertainty arises.

Cosmetic uniformity and color control

Films can give your brick a uniform, consistent look. But remember, they hide the natural texture of the brick.

Moisture can get trapped under these films. This could lead to problems later on.

If you’re after that smooth, even finish, consider it. Just know the trade-offs.

Below-grade waterproofing vs above-grade coatings

Below-grade membranes are designed to keep water out when used with a proper drainage system. They’re for underground parts of your wall.

Above-grade films, on the other hand, can trap moisture against the brick. This is bad news for your walls.

Use below-grade membranes where they’re meant to go. Above-grade, stick to breathable sealers.

Temporary protection during renovation

Short-term protective films can be useful while you’re working on your brick. They keep dirt and damage out.

But remember, they’re not a fix for moisture problems. Once the work’s done, those films need to come off.

Use them during renos, but don’t leave them on as a permanent solution.

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Avoid sealing when active leaks or rising damp are present, and when the mortar and brick are deteriorating. In these cases, addre