Should you seal brick? For most walls, no. Brick that is kept watertight at its joints, copings, flashing and gutters does not need a coating, and a film-forming sealer on older brick can trap water and salts that break the face off. A breathable, penetrating water repellent can make sense in a narrow set of cases: after the real leak paths are fixed, the wall has dried out, and water still comes through a particular area.
True Course Masonry Newark repairs and repoints brick across Newark and Essex County, with the work carried out by licensed and insured contractors. Sealing is not a substitute for that work, and this guide explains why. The masonry repair services page shows the repairs that usually solve the problem a sealer is bought for.
Why the question comes up
Homeowners report damp walls, white salt marks and flaking brick, and a clear sealer looks like the simplest answer. Sealing does not stop leaks by itself, though, because most water reaches a wall at its weak details. National Park Service guidance on historic masonry, Preservation Brief 1, Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings, says water penetration is seldom due to porous masonry and almost always results from leaking roofs, failed gutters and downspouts, missing mortar, or cracks and open joints around openings. Those are repair problems. The chimney leak guide shows how that plays out on a chimney.
Repellents vs sealers vs waterproof coatings
The products get called the same thing on the shelf, but they work in opposite ways.
| Product type | How it works | Effect on drying | Where it can fit |
|---|---|---|---|
| Penetrating water repellent (silane, siloxane and similar) | Soaks slightly into the surface and makes pores shed liquid water | Lets water vapor pass, but still reduces vapor movement somewhat | Selected areas of sound, repaired brick where water still penetrates |
| Film-forming clear sealer (acrylic and similar) | Forms a film on the face | Slows vapor and drying more; can look glossy or darken brick | Rarely suited to older brick walls |
| Waterproof coating (elastomeric paint, bituminous or cement-based coating) | Opaque layer that blocks liquid water and vapor | Stops outward drying through the face | Generally not suited to above-grade older brick walls |
Brief 1 is careful on this point. Water repellents, often wrongly called sealers, are meant to keep liquid water out while letting vapor in and out. Waterproof coatings seal the surface against both. Even the breathable products reduce vapor movement, and vapor that condenses inside a wall turns to liquid water that cannot escape through a repellent.
The risks on old brick
Trapped water and salts
An older solid brick wall has no cavity or flashing. It handles rain by soaking it up and drying it out again. Anything that slows drying through the face keeps the outer brick wetter for longer. In Newark that matters: NOAA’s climate normals for the Newark Liberty International Airport station count about 80 days a year with a low at or below freezing, and wet brick that freezes loses its face.
Salts are the second problem. Water carries dissolved salts through the wall. Without a coating, many reach the surface as efflorescence, the white powder covered in the efflorescence guide. With a coating that slows evaporation, they can crystallize just behind the face instead, as subflorescence, and push it off. Brief 1 warns that repellents can be especially damaging on masonry that contains salts. Deicing salt splashed onto low courses and stoops makes this a real risk at street level.
Rising damp and damp walls
Where moisture wicks up from the ground into the bottom of a wall, a coating does not stop it and can push the wet zone higher by slowing evaporation. Brief 1 also says a repellent should never be applied to a damp wall, because if it adheres at all it holds moisture inside.
Appearance and reversibility
Some coatings darken brick, leave a sheen or yellow with age. Most cannot be fully removed once they soak in. Failure is hard to judge: a test patch shows whether a product changes the look of the brick, but not whether the wall can still breathe, because water moves around the small treated area.
When a repellent can make sense
Brief 1 describes a narrow case. If, after the building has been made watertight and has dried completely, water still appears to come through the repaired walls, a repellent may be considered in selected areas only, not across the whole building. It also notes that very soft, underfired early brick can need some form of protection. In practice the order of work is:
- Fix the water paths. Repoint open joints, repair copings and sills, correct flashing, clear gutters and redirect downspouts. The brick pointing service page and the parapet repair page cover the two most common sources.
- Replace failed brick. Units that have lost their faces are cut out and replaced, as the brick repair service page describes.
- Let the wall dry. Give it time, including a season of weather, to show whether the repairs solved the problem.
- Only then consider a repellent, limited to the area still taking on water, with a product that is vapor permeable and suited to the brick. Never on a damp wall or over salt deposits.
Cleaning, painting and other coatings
Cleaning before a coating is a common pairing, and it carries its own risks; the guide to cleaning brick without damage covers them. Painted brick is a separate case: paint already acts as a coating, and stripping or repainting it needs the same thinking about drying. Where a house has been coated in the past and the brick beneath is flaking, the coating may be part of the cause, and the spalling brick guide explains how that happens.
What to take away
If someone recommends sealing as the fix for a leak, ask what path the water is taking and what repairs come first. A sound answer names joints, flashing, copings or gutters before any product. The when to repoint brick guide helps you judge whether your joints are the real problem.