Reduce Surface Absorption
A penetrating repellent can reduce the amount of wind-driven rain absorbed by porous masonry during exposure.
Masonry Water Repellents
Should You Seal Brick or Stone?
Sometimes a masonry water repellent is useful. Often it is unnecessary. And in the wrong situation, “sealing” brick or stone can slow drying, trap moisture and make deterioration worse.
The first distinction is important: a penetrating water repellent is not the same thing as a film-forming waterproof coating. The second question is even more important: why is the masonry getting wet?
Coatings change how masonry dries. Before adding another layer, identify whether the wall is wet because of rain absorption or because water is entering through cracks, flashing, joints, grade or another source.
Do not use a sealer to avoid repairing a leak.
What to Fix First
Two Very Different Treatments
“Masonry sealer” can describe products that behave very differently.
The label on the bucket matters less than what the treatment actually does to liquid water and water vapor.
Penetrating Water Repellent
Typically designed to soak into the pore structure and reduce absorption of liquid rainwater while remaining relatively open to water-vapor movement. Silane and siloxane chemistries are common examples.
Film-Forming Coating
Forms a more continuous layer over the masonry. These coatings can reduce drying much more strongly and may peel, blister or trap moisture behind the surface, especially on exterior walls exposed to freezing.
What Water Repellent Can Do
A suitable treatment can reduce rain absorption, but its job is limited.
It should be considered one tool in a water-management strategy, not a universal masonry repair.
Leave the Appearance Mostly Unchanged
Some penetrating products are nearly invisible when correctly selected and tested, although appearance changes are still possible.
Remain More Vapor Open
Breathable repellents are intended to allow more drying than dense film-forming waterproof coatings.
Reduce Repeated Wetting
In a carefully selected application, lower rain absorption can reduce how frequently the outer masonry becomes saturated.
Support a Repaired Wall
A repellent may be considered after cracks, joints, flashing and other water entry defects have already been corrected.
Require Future Maintenance
Water repellents are not permanent. Performance changes over time and retreatment should be based on actual condition rather than a fixed calendar.
What It Cannot Fix
A treatment on the face cannot repair defects that deliver water behind it.
Brick Industry Association guidance recommends correcting conditions that contribute to water penetration before applying a clear coating.
That includes open mortar joints, failed sealant, cracks, missing or damaged flashing, blocked drainage, roof runoff and other defects that let water enter the wall through paths a surface treatment cannot bridge reliably.
If liquid water is already getting behind the masonry, slowing evaporation at the face may make the wall wetter rather than drier.
A sealer does not replace
×Repointing failed mortar joints
×Repairing cracks or displaced masonry
×Proper flashing and weeps
×Window and door perimeter repairs
×Roof, gutter or chimney repairs
×Foundation grading and drainage
Find the entry point first. Flashing, caps, joints and roof intersections often matter more than the absorption of the brick itself.
Before You Seal Anything
Work through the ordinary water-entry paths first.
1Inspect mortar joints and cracked units
2Check flashing, weeps and drainage openings
3Check window and door sealant transitions
4Look at roof runoff, chimney crowns and caps
5Check grade and foundation drainage
6Allow repaired masonry to cure and dry before treatment
7Test the proposed treatment on a small representative area
Why Freeze-Thaw Changes the Risk
Anything that keeps more liquid water inside masonry can increase winter damage.
Freeze-thaw deterioration depends heavily on how wet the masonry becomes before it freezes. Saturated pores provide less room for ice expansion and can create damaging internal stresses.
Brick Industry Association Technical Note 6A specifically recommends against film-forming coatings on brickwork in freeze-thaw environments.
A breathable penetrating repellent is less restrictive than a film coating, but even breathable products reduce vapor permeability to some degree. That is why trapped moisture, rising damp, roof leaks and internal water sources should be addressed before treatment.
Read the freeze-thaw masonry guide →
Spalling is a moisture problem before it is a coating problem. Do not assume a sealer can save brick that is already saturated, damaged or receiving water from behind.
Historic Brick & Stone
Older masonry deserves more caution because drying and salt movement are part of how the wall survives.
National Park Service guidance says water-repellent coatings are frequently applied to historic masonry for the wrong reason and are often unnecessary when roofs, gutters, mortar joints and openings are maintained.
Older brick, soft stone and lime-rich mortar can be more sensitive to changes in drying. Soluble salts can also move with moisture through the wall. If evaporation is redirected beneath the surface, salt crystallization can damage the masonry internally.
A water repellent is also not a consolidant. It should not be expected to strengthen friable stone, restore lost brick faces or hold deteriorated material together.
Read the historic mortar compatibility guide →
Historic walls are systems. Brick or stone, mortar, interior finishes and exterior exposure all influence where moisture enters and how the wall dries.
Peeling tells you the coating and moisture are interacting. Before recoating, determine whether water is moving through the wall from behind the failing finish.
Film-Forming Coatings
Paint, clear films and waterproof membranes can create a different moisture problem.
A film-forming coating can reduce liquid water entry from the face, but it can also reduce the wall's ability to dry outward.
If water gets behind the coating through cracks, leaks, rising damp or interior vapor, it may become trapped against the masonry. Peeling, blistering, efflorescence and spalling can follow.
This is especially risky on old exterior brick and stone in cold climates. Removing an inappropriate coating can also be difficult, expensive and potentially damaging to the masonry surface.
When a Water Repellent May Be Reasonable
The case should be specific, not routine.
A treatment makes more sense when the wall has already been repaired and a defined rain-absorption problem remains.
After Repairs Are Complete
Cracks, joints, flashing, sealant and drainage defects have been corrected and the masonry has been allowed to cure and dry.
A Specific Exposure Problem Remains
The wall receives severe wind-driven rain or has unusually absorptive masonry where reduced surface uptake is part of a documented repair strategy.
The Product Matches the Substrate
The manufacturer supports use on the specific brick or stone and comparable installations have demonstrated appropriate performance.
Testing Shows Acceptable Results
A representative test area confirms acceptable appearance, absorption, penetration and drying behaviour before the whole wall is treated.
When Not to Seal
There are several conditions where adding a treatment should wait.
!The wall is already damp or saturated
!Efflorescence or salt activity is ongoing
!Brick or stone is actively spalling
!Mortar joints are open or deteriorated
!Flashing, roof or window leaks are unresolved
!Rising damp or foundation moisture is present
!The product creates a dense film in a freeze-thaw exposure
!The masonry type and previous coatings are not yet understood
Efflorescence means water has been moving through the masonry. Treat that as a diagnostic clue before reducing the wall's ability to dry.
Brick vs Stone
Do not assume one product is suitable for every masonry material.
Fired clay brick, sandstone, limestone, granite, concrete masonry and cast stone have different pore structures, absorption characteristics and sensitivities.
Brick Industry Association guidance is specifically written for fired clay brick and warns against assuming the same recommendations apply to other masonry products.
Natural stone varies even more widely. A treatment that penetrates one porous sandstone may sit differently on a dense granite or alter the appearance of a limestone. Testing should therefore be material-specific.
For historic or unusual stone, conservation guidance or material testing may be appropriate before widespread application.
Stone is not one material. Density, mineralogy, porosity and finish can all change how a water repellent behaves.
Atlantic Canada Context
Wind-driven rain and freeze-thaw make product selection especially important here.
Across Prince Edward Island, Nova Scotia and New Brunswick, exposed masonry can see coastal winds, repeated wetting, snow, spring melt and frequent freezing and thawing.
That combination makes both rain resistance and drying important. A treatment that reduces wind-driven rain can be useful in the right situation, but one that traps moisture can create exactly the saturation problem that winter masonry needs to avoid.
The practical regional approach is to repair water-entry defects first, keep masonry able to dry and use a water repellent only when there is a clear reason and a compatible product.
Control concentrated water before treating the surface. No repellent should be expected to compensate for a wall that is being soaked by runoff or defective drainage.
What to Photograph Before Asking About Sealer
Show the wall condition and the likely water sources.
Whole Elevation
Show the entire affected wall, roofline, openings and areas of different exposure.
Mortar & Brick or Stone
Include open joints, spalling, cracks, salts and any material deterioration.
Existing Coatings
Photograph peeling paint, gloss, discoloration or areas that appear previously treated.
Flashing & Openings
Show windows, doors, lintels, sills, flashing and sealant transitions.
Water Sources
Include gutters, downspouts, roof intersections, grade and splashback areas.
Interior Evidence
If leakage is part of the concern, show the matching interior staining or damp area.
Technical References
Why reputable guidance treats water repellents as selective treatments rather than routine maintenance.
National Park Service Preservation Brief 1 distinguishes vapor-permeable water-repellent coatings from waterproof coatings and warns that even modern repellents reduce vapor permeability to some degree. It says most historic masonry buildings do not need a water-repellent treatment when normal maintenance defects are corrected.
Brick Industry Association Technical Note 6A says a water-repellent coating is not necessary for normally exposed brickwork when material selection, design, construction and maintenance are sound. It recommends correcting water-entry conditions first, using breathable products and avoiding film-forming coatings in freeze-thaw environments.
BIA Technical Note 7A also emphasizes that coatings only help when the treatment matches the actual nature of the water-penetration problem.
NPS Preservation Brief 1: Cleaning & Water-Repellent Treatments →
Brick Industry Association Technical Note 6A: Colorless Coatings →
Brick Industry Association Technical Note 7A: Water Penetration Resistance →
About the Author
Prepared by Dean MacArthur, DinoMac Masonry Ltd.
Dean is a third-generation mason with more than 20 years of hands-on experience working with brick, natural stone, chimneys, foundations, repointing and masonry restoration in Prince Edward Island.
The DinoMac Masonry Knowledge Centre uses PEI field experience to explain masonry conditions that are also common across Atlantic Canada and other cold, wet climates.
Last reviewed: August 26, 2026
Masonry Sealer FAQ
Common homeowner questions.
Should brick be sealed?
Usually not as routine maintenance. Repair defects first and consider a breathable repellent only for a specific, justified exposure problem.
Should natural stone be sealed?
It depends on the stone, exposure and wall. Natural stones vary widely, so product selection and testing should be material-specific.
Water repellent or waterproof coating?
Penetrating repellents reduce liquid absorption while remaining more vapor open. Film coatings create a denser surface and carry greater trapping risk.
Will sealer stop a leaking brick wall?
Not if water is entering through failed flashing, open joints, cracks, blocked drainage or other construction defects.
Can sealer make spalling worse?
Yes. A treatment that traps moisture can increase saturation and freeze-thaw damage, particularly with film-forming coatings.
Is sealing permanent?
No. Service life varies with product, substrate, preparation and exposure. Treatments should be considered maintenance items, not permanent cures.
Related Knowledge Centre Guides
Fix the water source and masonry condition before deciding whether a repellent belongs in the repair.
Thinking About Sealing Masonry in PEI?
Find out why the wall is wet before adding a coating.
Send wide photos of the wall, close-ups of brick or stone and mortar, existing coatings, flashing and openings, nearby roof or drainage conditions and the PEI property location. DinoMac can help determine whether the masonry needs repair, improved water management or whether a water-repellent treatment is worth considering at all.