No, sealing your brick will not protect it from water damage. Film-forming brick sealers trap moisture inside the wall. When that moisture freezes in an Illinois winter, it expands by approximately 9 percent by volume inside the brick pore structure, fracturing the face from the inside. The result is spalling caused by the sealer, not prevented by it. The real waterproofing work is intact mortar joints, functioning flashing, and proper drainage. None of those come in a spray can.
This failure mode runs on a predictable schedule in our service area. A homeowner sees efflorescence or surface roughness, applies a product from a home improvement store, and by April they are looking at new spalling on a wall that was in reasonable condition six months earlier. We see it every spring.
How Brick and Mortar Handle Water
A brick masonry wall is not waterproof. It was never designed to be. It is designed to manage water: to limit the rate of liquid entry, to buffer moisture within the wall assembly, and to release absorbed moisture through evaporation and vapor movement when conditions allow.
Wilmette: Where the Sealer Temptation Is Strongest
Wilmette is where we see this mistake most often, and the reason is specific to the village. Wilmette’s primary documented masonry problem is efflorescence on basement and foundation walls, driven by a high water table and the lake-proximity humidity that comes with being directly adjacent to Lake Michigan. White salt crystals appear on foundation brick faces every spring. Homeowners see them and reach for a product that promises to seal the wall.
The timing makes it worse. Efflorescence is visible in spring, when the ground is still shedding winter moisture and the water table is at its highest. The homeowner applies a film-forming sealer in May or June. By the following February, the moisture that had been migrating through the foundation wall all autumn is now trapped inside it. The hard freeze in January or February expands that moisture by approximately 9 percent by volume inside the pore structure. By April, the spalling starts.
What Wilmette foundation walls actually need is repointing of deteriorated mortar joints, drainage improvements to reduce how much water contacts the exterior of the foundation, and in some cases breathable drainage board on the exterior. The efflorescence is not a sign the wall needs a coating. It is a sign that moisture is moving through the wall and the wall is doing its job: drying outward. Seal that drying path and you have converted a manageable situation into a structural one.
Brick is a ceramic material fired from clay. Its pore structure is a network of fine capillaries that absorb liquid water when the brick surface is wet and give up that water by evaporation when the surface dries. Softer, less densely fired brick from the early twentieth century absorbs water more readily than modern hard-fired face brick. Wilmette homes built in the 1920s to 1940s with soft Chicago common brick are the most vulnerable to sealer damage, because soft brick has a larger pore structure and more surface area to fracture when moisture freezes inside it.
Mortar joints are more permeable than most brick. Properly specified mortar is the primary moisture management element in the wall because it is where most of the water entry occurs and where most of the vapor movement happens. Sound mortar joints limit water entry to what the system can buffer and release. Cracked, recessed, or missing mortar creates pathways for direct water infiltration that the wall cannot accommodate. BIA Technical Note 8 identifies mortar permeability properties and their role in the moisture management system of a masonry wall.
The physics of the system mean that moisture management depends on the wall being able to dry. Block that outward drying path with an impermeable film, and you have changed the system from one that manages moisture to one that accumulates it.
The Sealer Sales Pitch, Northbrook, and Glenview
Masonry sealers are sold on the premise that water is bad for brick and that coating the surface will prevent water from getting in. The first part of that premise is partially true: excessive and chronic moisture is a problem for masonry. The second part is misleading, because the primary entry path for water in a masonry wall is not through the brick face. It is through the mortar joints. The coating does nothing about the joints while creating a vapor barrier that disrupts the wall’s ability to dry.
Northbrook and Glenview illustrate this precisely. Both villages built heavily between the 1960s and 1980s, with hard machine-pressed brick and builder-grade mortar that is now reaching its service life. Median home age in Northbrook is around 1968; in Glenview around 1965. The mortar is eroding. Homeowners see surface roughness and moisture staining, and reach for a can of sealer.
Builder-grade mortar failure is a joint problem, not a brick face problem. The mortar joints are where the water is entering. A film-forming sealer closes nothing at the joints, and it prevents the wall from drying the way it is designed to. On a Northbrook split-level with 40-year-old eroding mortar, the trapped moisture has multiple entry paths through the joints and one blocked exit path through the sealed face. The wall becomes a moisture trap. The correct answer is tuckpointing, not coating.
A surface treatment applied to brick with sound joints, correct flashing, and proper drainage adds almost nothing to the wall’s water resistance. Applied to a wall with deteriorating joints, it seals moisture in while the real problems continue.
Film-Forming Sealers: What They Do to a Wall
A film-forming sealer creates a continuous coating on the brick surface. It is relatively impermeable to both liquid water and water vapor: essentially a plastic or silicone membrane adhered to the outside of the wall.
The primary effect is to prevent the brick face from absorbing liquid water. The damaging secondary effect is to prevent the brick and mortar behind the film from releasing moisture vapor outward. Moisture that enters the wall through the joints, through cracks in the film, through flashings that are not perfectly sealed, or through vapor condensation inside the wall assembly is trapped.
In Chicago’s climate, with dozens of freeze-thaw cycles each winter, trapped moisture in the brick pore structure freezes and thaws repeatedly. Each freeze cycle expands the water by approximately 9 percent by volume, stressing the pore walls from the inside. On soft historic brick, this pressure fractures the face relatively quickly. On harder modern brick, the damage takes longer to appear but the mechanism is the same. For a detailed look at how this produces the spalling you see in spring, see What Causes Brick Spalling and How to Prevent It.
The film itself also deteriorates over time. UV radiation, thermal cycling, and moisture cycling break down the coating over years. As it crazed and detaches in patches, water enters wherever the film has lifted, but the brick behind intact sections still cannot dry outward. The result is concentrated moisture accumulation exactly where the film is failing.
What Sealing Does to an Already-Damaged Wall
Applying a film-forming sealer to a wall that already has deteriorating mortar joints or early spalling damage compounds the problem. Water that enters through cracked joints is now sealed into the wall because the face cannot breathe. The sealer creates a new constraint on top of an existing moisture management failure.
Evanston: Portland Cement on Soft Brick, Then a Sealer on Top
Evanston is where we see the most severe version of this pattern. The city has the oldest residential masonry stock on the North Shore, with many homes exceeding 100 years and built with soft Chicago common brick that requires lime-based mortar. Many were repointed in the 1970s or 1980s with Portland cement mortar, harder than the original brick. That mismatch already reduces the wall’s ability to release moisture outward, because Portland cement has lower vapor permeability than lime mortar.
When a homeowner applies a film-forming sealer on top of that situation, there are now two barriers between the trapped moisture and the outside air. The brick is soft, old, and absorbs moisture readily. The moisture has nowhere to go. The first hard freeze causes brick face fracturing that looks like the brick is simply aging. What is actually happening is that two wrong decisions compounded: the wrong mortar on soft historic brick, then a sealer that eliminated the wall’s remaining ability to dry.
Evanston greystones carry an additional complication. These buildings use Indiana limestone facing on the front facade over common brick on the sides and rear. Limestone is more porous and less freeze-thaw resistant than well-fired brick. A sealer applied to the limestone facing traps moisture in a material already more vulnerable to fracturing. The common brick sides may handle the same conditions better than the limestone front, which can mislead a homeowner into thinking the sealer worked on most of the building.
This pattern is also common in Deerfield, where 1960s and 1970s colonials with steel lintels are already prone to rust-jacking along the lintel courses. A homeowner who seals the facade in response to staining at the lintel line traps moisture at precisely the location where the steel is actively corroding and expanding. The sealer accelerates the lintel failure it was meant to prevent.
For efflorescence specifically, the white deposits are mineral salts carried to the surface by evaporating moisture. If the moisture cannot evaporate outward through the face because the face is sealed, the salt deposition occurs behind the sealer film, between the film and the brick surface. This is called sub-efflorescence, and it generates crystallization pressure within the pore structure that causes spalling. See Efflorescence and White Staining in Spring: What It Means for how to read these signs on your own wall.
Vapor Permeability: Why It Matters
The technical term for a material’s ability to allow water vapor movement is vapor permeability. Materials with high perm ratings allow vapor to pass freely. Materials with low perm ratings restrict vapor movement.
Original lime mortar has a relatively high perm rating. It allows the wall to breathe. Modern Portland cement mortar has a lower perm rating, which is one reason that high-Portland-content mortar on historic soft brick can cause problems: the reduced vapor permeability means the wall dries more slowly, increasing freeze-thaw risk. For the full explanation of why mortar composition matters, see Lime vs. Portland Cement Mortar.
Film-forming sealers have perm ratings close to zero. They are designed to be vapor barriers. Applying them to a masonry wall that needs to breathe to manage moisture is applying a vapor retarder to a wall whose moisture management system depends on vapor movement. The system cannot function as designed.
Penetrating silane or siloxane treatments have much higher perm ratings than film-forming sealers. They work by lining the pore walls in the brick with a hydrophobic molecular layer, which reduces capillary uptake of liquid water without creating a surface film. The wall can still dry through vapor movement. NPS Preservation Brief 1 covers the assessment of water-repellent treatments on historic masonry, distinguishing between products that allow vapor movement and those that create problematic vapor barriers. This is fundamentally different from film-forming products, and the distinction matters when evaluating any masonry treatment.
The Narrow Case for a Breathable Treatment
Penetrating silane or siloxane treatments can add value in a specific set of conditions. The wall must be in sound structural condition: mortar joints must be intact and properly specified, flashing must be functional, and there should be no active moisture infiltration. The treatment is an upgrade to an already-well-functioning wall, not a solution to a moisture problem.
The application scenario that makes the most sense is a wall in excellent condition on a building that faces heavy wind-driven rain, particularly on an exposed north or west elevation in an open site. A vapor-permeable treatment reduces the rate of liquid water absorption during rain events, which reduces the total moisture burden on the wall, without interfering with the wall’s ability to dry between events.
Even in this narrow case, the treatment requires periodic maintenance. Penetrating silanes and siloxanes do not last indefinitely. Depending on exposure conditions and the specific product, reapplication may be needed every five to fifteen years. And the treatment never substitutes for sound mortar joints and functional flashing. If the mortar has deteriorated, the treatment is addressing a secondary factor while the primary entry point remains open.
Before any treatment is applied to a masonry wall, the joints should be assessed by a masonry professional. On walls where tuckpointing is needed, the correct sequence is to tuckpoint first and then, if treatment is warranted at all, apply it after the mortar has cured. NPS Preservation Brief 2 specifies joint removal to a minimum 3/4 inch depth per BIA Technical Note 7B as the standard for repointing that actually reaches sound material. Applying any treatment over deteriorating mortar or repointing over treated surfaces creates compatibility problems.
For more on tuckpointing and why properly applied mortar is the primary line of defense, see the Understanding Tuckpointing: A Complete Guide for Illinois.
What Actually Keeps Water Out
The real waterproofing system in a brick masonry wall is a combination of elements that work together. None of them are a product applied to the surface. All of them require periodic maintenance.
Sound mortar joints. Cracked, recessed, or missing mortar joints are the primary water entry path in a masonry wall. Tuckpointing deteriorated joints closes the entry paths. On pre-1920 homes, this means using lime-compatible mortar; on later construction, the appropriate specification depends on the brick and existing mortar. The minimum compressive strength of 750 PSI for Type N mortar under ASTM C270 is the standard for above-grade residential work; using Type S at 1,800 PSI minimum on soft historic brick causes the brick to fail rather than the mortar.
Functioning flashing. Flashing at window heads, shelf angles, parapet bases, and roof-to-wall intersections directs water that has entered the wall cavity back outside. Failed flashing allows water to travel into the wall assembly and building structure. Water damage attributed to leaking brick is often actually failed flashing. Flashing condition is part of any complete masonry repair assessment.
Weep holes. Weep holes at the base of the brick veneer allow water that enters the cavity to drain outward rather than accumulate. They are often clogged with mortar droppings or blocked by renovation work. A wall with failed flashing and blocked weep holes has no drainage path for cavity water. See Weep Holes in Brick Walls: Drainage Explained for how the full drainage plane system works.
Intact cap details. Chimney crowns, parapet caps, and window sills are horizontal surfaces at the tops of masonry elements. Water that sits on these surfaces enters the masonry directly. A cracked chimney crown allows water to infiltrate the chimney structure with every rain event. A parapet cap with failed caulk joints saturates the parapet in every storm. These are high-priority maintenance items because water entry at the top of a masonry element travels downward through the full height of the element before appearing as damage at lower levels. See Parapet Wall Repair for how cap failures on flat-roof buildings drive repair decisions.
Grading and drainage. Water that pools against the foundation from surface runoff or inadequate grading creates chronic hydrostatic pressure on the below-grade masonry. Appropriate grading that directs water away from the building perimeter and downspout extensions that discharge away from the foundation reduce the below-grade moisture load.
When Someone Tries to Sell You a Sealer
A contractor proposes sealing the brick as part of a spring maintenance program. Here is the question to ask: is this a film-forming sealer or a penetrating treatment, and what is its perm rating?
A contractor who cannot answer that question is selling a product category without understanding the product. A film-forming product applied to a Chicagoland home is, in most cases, going to cause more damage over a five-year period than it prevents in the first rain event. The freeze-thaw mechanism is reliable and the moisture load in a Chicago winter is sufficient to produce measurable spalling on soft historic brick within a single season.
If a penetrating, vapor-permeable treatment is proposed, the follow-up question is whether the mortar joints are in sound condition. If tuckpointing is needed, that comes first. No surface treatment compensates for failed mortar, and the correct sequence is to close the entry paths before addressing secondary factors.
What should actually be on the maintenance checklist is an honest look at the mortar joint condition across the wall, an inspection of flashing at window heads and roof transitions, a check of the chimney crown or parapet cap, and a look at grading and drainage around the perimeter. Also see How to Clean Brick Safely for the surface cleaning sequence that goes with a sound mortar assessment. That inspection is worth more than any can of sealer.
Getting the Assessment Right
For a masonry assessment on your home in Northbrook, Glenview, Wilmette, Evanston, Deerfield, or anywhere across Chicagoland’s North Shore and northwest suburbs, the right starting point is understanding what the wall actually needs, not what a product label claims to offer.
Delta - Masonry and Tuckpointing has been working with brick and mortar across this region since 1987. We assess mortar joint condition, inspect flashing and cap details, and specify tuckpointing and masonry repair work based on what is actually failing in the wall. We do not apply film-forming sealers to masonry walls, and we will tell you plainly if a surface treatment is not what your wall needs.
For homeowners in Arlington Heights and Palatine, we cover the northwest suburbs as well. Call (847) 713-1648 or contact us online to schedule a free on-site assessment.
Brick sealer is a product category that sells well and solves almost nothing. The real waterproofing system is sound mortar, working flashing, and drainage. That system does not come in a spray can.