Should You Seal Chicago Brick? What a Sealer Does and Does Not Fix

By Affordable Tuckpointing Pros, a Chicago tuckpointing and brick repair company in business since 1996. License number MC6337.

Direct answer

Usually no. NPS states that the application of water-repellent coatings to historic masonry is usually unnecessary, and that water getting into a masonry building is seldom due to porous masonry but results from poor or deferred maintenance. [1] BIA goes further for this climate: do not apply film-forming coatings to brickwork located in freeze-thaw environments. [2] Fix the joints, the sills, the copings and the gutters first, and the coating is almost always unnecessary after that. [1] [2] [3]

TL;DR

• A “sealer” is usually the wrong word for the product. NPS says water-repellent coatings are often referred to incorrectly as sealers, but do not or should not seal. [1]
• Water-repellent and waterproof coatings are different things. A repellent keeps liquid water out but lets vapor pass; a waterproof coating seals the surface to both. [1]
• Sealers do not close the route water actually takes. BIA says water usually penetrates at cracks and separations between brick and mortar, and that penetrating repellents seldom stop water through cracks wider than 0.02 in. [2]
• In a freeze-thaw climate the risk runs the other way. NPS says water trapped behind a coating can freeze and cause serious mechanical disruption such as spalling. [1]
• BIA names the condition Chicago is in: do not apply film-forming coatings to brickwork in freeze-thaw environments. [2]
• The sequence is not optional. BIA says correct the conditions contributing to water penetration before applying a coating, and inspect and correct all deficiencies before considering external coatings at all. [2] [3]
• It is not permanent and it may not be removable. BIA puts water repellents on walls at 5 to 10 years, and NPS says these coatings can be very difficult, if not impossible, to remove if they fail or discolour. [3] [1]

One liner: A sealer is a bet that your wall is leaking through the brick. In Chicago it is almost always leaking through the joints, the sills and the copings instead.

What does a brick sealer actually do?

In short: Most products sold as sealers are water repellents, which slow absorption into the face of the brick while still letting vapor out. That is a much narrower job than the name suggests.

The vocabulary is the first problem, and NPS addresses it head on. It says it is important to understand that waterproof coatings and water-repellent coatings are not the same, that the terms are frequently interchanged and commonly confused, and that they are completely different materials. [1] A water-repellent coating is intended to keep liquid water from penetrating the surface but to allow water vapor to enter and leave, or pass through, the surface of the masonry. A waterproof coating seals the surface from liquid water and from water vapor, and NPS lists bituminous coatings and some elastomeric paints in that group. [1]

NPS is also direct about the marketing term itself: water-repellent coatings are often referred to incorrectly as sealers, but they do not, or should not, seal. [1] If a product on your building is genuinely sealing the brick to vapor, that is not a better version of a repellent. It is the category NPS says should almost never be applied above grade to masonry buildings. [1]

The modern repellents themselves have moved on from the early acrylic and silicone resins. NPS describes most current products as water-based and formulated from modified siloxanes, silanes and other alkoxysilanes, or metallic stearates, penetrating slightly into the substrate rather than forming a film on top, and generally almost invisible if properly applied. [1] BIA suggests considering a siloxane or siloxane and silane pre-blended coating where one is used at all. [2]

But here is the line that matters for a Chicago building, and NPS does not soften it: these coatings are more vapor permeable than the old ones, yet they still reduce the vapor permeability of the masonry. [1] Every sealer, including the good ones, makes your wall dry more slowly than it did before. Whether that is acceptable depends entirely on whether you have fixed the reason water is getting in.

Why sealing does not stop the leak you actually have

In short: Water gets into brickwork through cracks and junctions, not through the face of sound brick, and a penetrating repellent does not bridge cracks.

This is the technical heart of it. BIA states that water-repellent coatings are most effective at reducing the amount of water absorbed by brick masonry, but that water usually penetrates brick masonry at separations and cracks between brick and mortar, or at junctures with other materials. Because of that, a change in the absorption properties of the brick may not significantly reduce water penetration through the brickwork. [2]

Then it puts a number on the limit. Penetrating water-repellent coatings seldom stop water penetration through cracks more than 0.02 in. wide, and their effectiveness under conditions of wind-driven rain is limited. [2] Half a millimetre. That is thinner than most hairline cracking you can see from the sidewalk, and far thinner than an open bed joint on a wall that is due for repointing.

BIA is equally clear about what a coating cannot compensate for: water-repellent coatings cannot stop water penetration caused by design or construction deficiencies such as ineffective sills, caps or copings, or incompletely filled mortar joints. [2] Those three items describe the majority of water problems on older Chicago buildings. A limestone sill that has lost its wash and now drains toward the wall, a chimney or parapet coping with open joints, a wall whose head joints were never fully filled: none of those are absorption problems and none of them respond to a coating.

NPS reaches the same conclusion from the building-diagnosis side. Water penetration to the interior of a masonry building is seldom due to porous masonry, but results from poor or deferred maintenance, and leaking roofs, clogged or deteriorated gutters and downspouts, missing mortar, or cracks and open joints around door and window openings are almost always the cause of moisture-related problems. [1] Its conclusion follows directly: if masonry buildings are kept watertight and in good repair, water-repellent coatings should not be necessary. [1]

So the honest test before you spend money on a coating is to go and find the actual entry point. If it is an open joint, you need tuckpointing. If it is a sill or a coping, you need that detail rebuilt. If it is a gutter, you need a gutter. In none of those cases does the sealer do the work.

The freeze-thaw problem: why a coating can make Chicago brick worse

In short: Once liquid water is behind a coating it cannot get out as liquid, and in this climate it will freeze there.

A water repellent is a one-way arrangement, and the direction matters. NPS explains the failure precisely: once inside the wall, water vapor can condense at cold spots producing liquid water which, unlike water vapor, cannot escape through a water-repellent coating, and that liquid water within the wall, whether from condensation, leaking gutters, or other sources, can cause considerable damage. [1] Vapor gets out. Liquid does not. In a Chicago winter the wall is full of cold spots where vapor becomes liquid.

For fully waterproof coatings NPS spells out the consequence: in theory they do not cause problems as long as they exclude all water, but if water does enter the wall from the ground or from inside the building, the coating can intensify the damage because the water will not be able to escape, and during cold weather this water in the wall can freeze causing serious mechanical disruption, such as spalling. [1] It adds that the water eventually gets out by the path of least resistance, damaging interior finishes if that path runs inward, or damaging the masonry through built-up water pressure if it runs outward. [1]

BIA turns this into a flat instruction rather than a caution, and it is the single most relevant sentence in the literature for a building in this city: do not apply film-forming coatings to brickwork located in freeze-thaw environments. [2] Chicago is that environment. Any product that leaves a continuous film on the face of your brick is outside BIA’s recommendation here regardless of how it is marketed.

The National Park Service makes the same point in its general brick guidance without hedging: waterproofing the brick either with chemicals sold for that purpose, or by painting with non-permeable paint or other coatings, will accelerate the decay by trapping moisture behind the new coating. [4] If your brick is already spalling, this is the mechanism that takes it from a slow problem to a fast one. We cover the rest of that failure in why Chicago brick spalls.

Salt: the reason coatings are worse on the walls that look like they need them most

In short: A wall showing efflorescence is carrying salt, and NPS says coatings are especially damaging on masonry that contains salts.

Efflorescence, the white bloom on a brick wall, is what sends a lot of homeowners looking for a sealer in the first place. BIA describes it as white deposits left on the brick surface when moisture carrying dissolved salts evaporates. [3] On the surface it is mostly cosmetic and largely water soluble, removable by natural weathering, dry-brushing or scrubbing with a stiff fibre brush and water. [3]

The salt only becomes destructive when it crystallises inside the brick instead of on it. NPS says the salts can be potentially dangerous if they remain in the masonry and crystallise beneath the surface as subflorescence, and that subflorescence eventually may cause the surface of the masonry to spall. [1] Then it names the aggravating factor directly: this is particularly true if a water-repellent coating has been applied, which tends to reduce the flow of moisture out from the subsurface of the masonry. [1] It closes the point by noting that although many newer water-repellent products are more breathable than their predecessors, they can be especially damaging if applied to masonry that contains salts, because they limit the flow of moisture through masonry. [1]

Put those together and you get an uncomfortable result. The wall that visibly looks like it needs sealing, the one with white staining and damp patches, is the wall where a coating is most likely to cause spalling. Efflorescence is evidence of active moisture movement carrying salt. Coating it does not stop the moisture arriving, it stops the salt leaving harmlessly.

BIA’s instruction for efflorescence is diagnostic rather than cosmetic: scrutinise masonry with persistent efflorescence for unresolved water penetration issues, and investigate and resolve the water ingress before cleaning, because otherwise it will return. [3] That is the work. The white staining is a gauge reading, and the fix is upstream of it.

When a coating is actually appropriate

In short: Rarely, on selected areas only, after the building has been made watertight and has dried, and ideally with a conservator involved.

Neither source says never. They both say last, narrow, and only after everything else. NPS sets out the sequence: when a masonry building has been neglected for a long period, necessary repairs may be required to make it watertight, and if, following a reasonable period of time after the building has been made watertight and has dried out completely, moisture still appears to be penetrating through the repaired masonry walls, then the application of a water-repellent coating may be considered in selected areas only. [1] It adds that the decision should be made in consultation with an architectural conservator, and that if undertaken it should not be applied to the entire exterior of the building. [1]

Where it is justified is usually the worst-exposed detail rather than the field of the wall. NPS suggests that if the problem occurs on only part of the building it is best to treat only that area, and names extreme exposures such as parapets, or portions of the building subject to driving rain, as areas that can be treated more effectively and less expensively than the entire building. [1] It also notes one genuine case for a coating: soft, incompletely fired brick that has become so porous that some kind of coating is needed to protect it from further deterioration or dissolution. [1]

There are absolute exclusions too. NPS says a water-repellent coating should never be applied to a damp wall, because moisture reduces the coating’s ability to adhere and penetrate, and if it did adhere it would hold the moisture inside the masonry. [1] It says a coating will not solve rising damp or condensation and may be likely to exacerbate it, and in the case of rising damp may force moisture higher up the wall by slowing evaporation. [1] BIA adds that application is not recommended on newly constructed brick veneer or cavity walls, or on new or existing pavements using clay pavers. [2]

And BIA makes one practical point that rarely appears on a quote: consider providing vents at the top of drainage spaces when a water repellent coating is applied. [2] If you are going to slow the wall’s ability to dry outward, the cavity behind it needs another way to breathe.

How to judge a sealing quote if you are going ahead anyway

In short: BIA gives specific, checkable selection criteria, and a quote that cannot answer them is not a specification.

If a coating is genuinely warranted on your building, BIA’s recommendations give you a short list of things the contractor should be able to state in writing. They are worth reading as questions.

• Is it breathable enough? Except for anti-graffiti applications, BIA says to use only breathable coatings with a water vapor permeability of 0.98 or greater as measured by ASTM E96. [2]
• Is it formulated for clay brick? BIA says to select only coatings intended for use on clay brickwork, and notes that clear coatings formulated for other masonry materials may in fact be detrimental to brick, which has a different pore structure and is generally less absorptive, less permeable and less alkaline than concrete masonry. [2]
• Has the brick manufacturer been consulted? BIA lists that as a general selection criterion before a coating is chosen. [2]
• Does the product have a track record on work like yours? BIA says to select coatings that have demonstrated consistent performance on similar installations, materials and exposures for a minimum period of five years. [2]
• Does the contractor? BIA says to use a contractor with a minimum of five years experience installing the selected coating on similar installations. [2]
• Is the effectiveness being measured rather than asserted? BIA points to comparative testing of treated and untreated walls using ASTM E514 or ASTM C1601. [2]
• Is it a film former? If so, and you are in Chicago, BIA says not to use it. [2]

Two more things belong in the conversation. NPS warns that testing a coating on one small area may not tell you what you want to know, because water can enter and leave through the surrounding untreated areas, so there is no way to tell whether the coated test patch is breathable, although a test patch is still useful for judging whether the coating changes the appearance of the masonry. [1] And a coating is a recurring cost, not a capital one. BIA estimates 5 to 10 years for water repellents on walls before repairs are necessary, against 50 years and beyond for mortar and 100 to 150 years for the brick itself. [3] NPS notes the awkward corollary that if the coating is truly invisible, it can be difficult to know when it is no longer providing the intended protection. [1]

The irreversibility is the last thing to weigh. NPS says these coatings can be very difficult, if not impossible, to remove from the masonry if they fail or become discoloured. [1] Some change the appearance of the wall: NPS notes that some coatings darken or discolour certain types of masonry, while others give it a glossy or shiny appearance. [1] On a brick building that is the kind of mistake you look at for the rest of the time you own it.

What to do instead, in order

In short: Every authority here gives the same sequence: find the water, fix the detail, restore the joint, then reconsider whether a coating is needed at all.

BIA’s maintenance guidance puts the order plainly. Investigate and determine the moisture sources before attempting repairs to correct water penetration issues, and before considering application of external coatings, inspect masonry and correct all deficiencies. [3] Its coatings guidance repeats it: correct the conditions contributing to water penetration before applying a coating to brickwork. [2]

On a Chicago building, working that sequence usually means the following list, roughly in the order the money is best spent.

• Roof, gutters and downspouts. NPS names leaking roofs and clogged or deteriorated gutters and downspouts among the causes that are almost always responsible for moisture problems. [1]
• Caps, copings and sills. BIA’s inspection checklist flags inadequate slope, cracked units, open joints and missing drips on these elements, and notes that neglecting components such as caps, copings, sills and lintels may lead to deterioration of other elements in the wall. [3]
• Mortar joints. Missing mortar and open joints around openings are on the NPS list of usual causes, and repointing with a compatible mix is the core repair. [1] BIA recommends prehydrated Type N, O or K mortar for repointing. [3]
• Sealant joints. BIA says to remove and replace torn, deteriorated or inelastic sealants and backer rod, and estimates only 5 to 20 years of service from them. [3]
• Weeps and flashing. BIA says to carefully open clogged weeps without damaging existing flashing, and to drill new weeps where none exist. [3]
• Grade and drainage. BIA’s checklist includes grade and drainage alongside roof overhangs and gutters as items to inspect. [3]

Do that list and most Chicago walls stop leaking without a drop of coating, which is precisely what NPS predicts. [1] It is less profitable work to sell than a sealing package and it is the work that actually holds. If you want it scoped for your building, our masonry waterproofing and tuckpointing pages set out how we approach it, and what drives the price covers the numbers.

Brick sealing questions Chicago homeowners ask

Should I seal my brick house in Chicago?

Usually not. NPS says application of water-repellent coatings to historic masonry is usually unnecessary, and BIA says not to apply film-forming coatings to brickwork in freeze-thaw environments. [1] [2] Fix the joints, sills, copings and gutters first. [1] [3]

What is the difference between a water repellent and a waterproof coating?

A water repellent keeps liquid water from penetrating the surface but allows water vapor to pass through. A waterproof coating seals the surface to both liquid water and vapor. NPS says they are completely different materials and are commonly confused. [1]

Will a sealer stop my brick wall leaking?

Probably not, because it does not close the route the water is using. BIA says water usually penetrates at cracks and separations between brick and mortar, and that penetrating repellents seldom stop water through cracks wider than 0.02 in. [2] They also cannot compensate for ineffective sills, caps or copings or incompletely filled joints. [2]

Can sealing brick cause damage?

Yes. NPS says trapped water behind a coating can freeze and cause serious mechanical disruption such as spalling, and that subflorescence is particularly likely to spall the surface where a coating has reduced the outward flow of moisture. [1] NPS also says waterproofing brick will accelerate decay by trapping moisture behind the coating. [4]

How long does a brick sealer last?

BIA estimates 5 to 10 years for water repellents on walls before repairs are necessary. [3] NPS adds that if the coating is truly invisible it can be difficult to know when it has stopped working. [1]

Can a brick sealer be removed?

Often not. NPS says these coatings can be very difficult, if not impossible, to remove from the masonry if they fail or become discoloured. [1]

Is there any situation where sealing brick is the right call?

Yes, narrowly. NPS says a coating may be considered in selected areas only, after the building has been made watertight and has dried out completely, if moisture still appears to be penetrating, and in consultation with an architectural conservator. [1] Parapets and elevations taking driving rain are the typical candidates. [1]

Should I seal brick that is already spalling or damp?

No. NPS says a water-repellent coating should never be applied to a damp wall, because it would hold moisture inside the masonry. [1] A coating on already damaged masonry may form a surface crust that pulls off more material if it fails. [1]

What should I ask a contractor quoting a brick sealing job?

Whether the coating is a film former, its water vapor permeability under ASTM E96, whether it is formulated for clay brick, whether it has five years of documented performance on similar work, and whether the crew has five years experience with it. BIA lists all of these as selection criteria. [2]

Does sealing help with efflorescence?

No, and it can make it worse. BIA says to investigate and resolve the water ingress first or the efflorescence returns. [3] NPS says coatings can be especially damaging on masonry containing salts because they limit the flow of moisture through it. [1]

Stats box

Definition bank

Entity cards

Water-repellent coating

Waterproof coating

Freeze-thaw environment

Efflorescence

Spending the money where the water is

In short: Ask a contractor to show you where water is entering the wall before they quote you to coat it, and most sealing jobs turn back into repointing jobs.

Sealing brick is easy to sell because it sounds like protection and it covers an entire building in a day. The literature does not support it as a default. NPS says coatings on historic masonry are usually unnecessary and that water problems almost always come from deferred maintenance instead. [1] BIA says a repellent is not necessary to achieve water resistance in brickwork under normal exposures where material selection, detailing, construction and maintenance have been executed properly, and tells you not to use film formers in a climate like this one at all. [2]

So ask the question that separates a diagnosis from a product: where is the water getting in, and what are you doing about that? A contractor who walks the elevations and comes back with open joints, a coping with no slope, a sill missing its drip and a downspout discharging against the wall is describing your actual repair. One who quotes a whole-building coating without naming an entry point is selling you 5 to 10 years of something that does not address it. [3]

If you want that assessment in writing for your building, get a free quote from our team and we will tell you what we find.

Sources

1. National Park Service, Preservation Brief 1, “Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings”, Mack and Grimmer, 2000. https://www.nps.gov/orgs/1739/upload/preservation-brief-01-cleaning-masonry.pdf
2. Brick Industry Association, Technical Note 6A, “Colorless Coatings for Brick Masonry”, August 2008. https://www.gobrick.com/media/file/6a-colorless-coatings-for-brick-masonry.pdf
3. Brick Industry Association, Technical Note 46, “Maintenance of Brick Masonry”, December 2017. https://www.gobrick.com/media/file/46-maintenance-of-brick-masonry.pdf
4. National Park Service, “Common Problems with Brick Masonry”, Technical Preservation Services. https://www.nps.gov/articles/common-problems-with-brick-masonry.htm