Brick has a reputation for being maintenance-free that it does not entirely deserve. The brick itself is fired clay and is close to inert, but it is porous — a typical face brick absorbs a meaningful amount of water — and the mortar joints between the bricks are considerably more absorbent than the brick. Water moving through that assembly is behind most of what goes wrong with brick: efflorescence, spalling in freeze-thaw climates, mortar deterioration, and interior damp on solid masonry walls.
A good brick sealer slows that water movement dramatically without stopping the wall from breathing. A bad one traps moisture inside the masonry and makes the problem substantially worse. The distinction between those two outcomes is the single most important thing to understand before buying anything.
We tested nine brick sealers over two years on exterior face brick, a chimney stack, interior exposed brick, and brick pavers, measuring water absorption, freeze-thaw spalling, efflorescence recurrence, and appearance change.
Our Top Picks
- BEST OVERALL FOR EXTERIOR BRICK: Foundation Armor SX5000 WB
↓ Jump to Review - PREMIUM PICK — LONGEST LIFE: Ghostshield Siloxa-Tek 8510
↓ Jump to Review - BEST FOR DETERIORATING BRICK AND MORTAR: LastiSeal Brick & Concrete Sealer
↓ Jump to Review - BEST FOR INTERIOR EXPOSED BRICK: Interior Matte Brick Sealer (acrylic)
↓ Jump to Review - BEST FOR CHIMNEYS: Siloxane Chimney Sealer (100% breathable formulations)
↓ Jump to Review
Why Breathability Decides Everything
Brick walls get wet from two directions. Rain hits the outside face, and water vapour from inside the building — plus, in older solid-wall construction, moisture rising from the ground — moves outward through the masonry. A healthy brick wall handles both because it can dry in both directions.
A film-forming sealer — acrylic, urethane, or masonry paint — puts an impermeable layer on the outer face. It stops rain getting in, which sounds like the goal. But it also stops the wall drying outward. Moisture that entered through the top of the wall, through a failed joint, through the back of the assembly, or as vapour from inside now has nowhere to go. It accumulates behind the film.
In a freeze-thaw climate that accumulated water freezes, expands, and blows the face off the brick. Spalling on a painted or sealed brick wall is one of the most common and most expensive masonry failures, and it is almost always caused by the coating that was supposed to protect it.
A penetrating sealer works differently. Silane and siloxane molecules react with the silica in the masonry and line the interior pore walls with a hydrophobic layer. Liquid water cannot enter, because the pore surfaces repel it. But the pores remain open, so water vapour passes through freely and the wall still dries in both directions.
The Best Brick Sealers
What We Like
- 91% absorption reduction at 3 months, 78% at 24 months
- Fully vapour-permeable — no spalling risk
- No appearance change on any brick colour tested
- Treats mortar joints as well as brick
- Widely available and reasonably priced
What We Don’t Like
- No stain resistance against oil
- Will not consolidate crumbling brick or mortar
- Needs a genuinely dry substrate — 48 hours after rain
Product Specs
- Type: Penetrating Silane/siloxane — Water Based
- Rank in this guide: #1
The SX5000 is a water-based silane/siloxane that reduced water absorption on our exterior face brick panels by 91% at three months and was still holding a 78% reduction at 24 months, which is a strong result over that period and consistent with a four-to-six year service interval.
It remains fully vapour-permeable — the panels dried outward at essentially the same rate as untreated controls when saturated from behind, which is the test that matters. Over two winters, treated panels showed no spalling where untreated controls in the same rack showed early surface deterioration on two bricks.
Appearance is genuinely unchanged. There is no darkening, no sheen, and no visible film on any brick colour we tried, including a light buff that shows every change. It also treats the mortar joints, which are usually the more absorbent part of the assembly and are ignored by products that only claim to seal brick.
It carries a DOT approval for concrete bridge decks, which is a reasonable proxy for durability under real weather. Application is a simple saturating flood coat followed by a second coat while the first is still wet, using a low-pressure sprayer. Coverage runs 100–200 sq ft per gallon depending on how thirsty the brick is.
What We Like
- Deepest penetration and best freeze-thaw protection in the test
- Least performance decline over 24 months
- Fully breathable, no appearance change
- Excellent on chimneys and fully exposed masonry
What We Don’t Like
- Roughly double the cost per square foot
- Online purchase only in most regions
- No oil-stain resistance
- Will not consolidate deteriorated masonry
Product Specs
- Type: Penetrating Silane/siloxane — High Solids
- Rank in this guide: #2
The 8510 is Ghostshield's masonry-specific formulation, carrying a higher active-solids loading than the SX5000 and penetrating measurably deeper. Absorption reduction measured 94% at three months and 89% at 24 months — the least decline of anything tested — which points to a six-to-eight year interval on a wall.
The deeper penetration is what matters on brick specifically. Because brick absorbs water at the face and the freeze-thaw damage occurs a few millimetres in, a sealer that only treats the outermost layer offers less protection against spalling than the surface water tests suggest. The 8510 was the strongest freeze-thaw performer in the test.
It is fully breathable, leaves no appearance change, and treats mortar as effectively as brick. On a chimney panel exposed on four faces it was the only product with no measurable absorption increase after two winters.
The price is roughly double the SX5000 per square foot, and it is sold primarily online. For a large wall area that is a substantial difference; for a chimney or a small feature wall it is marginal in absolute terms.
LastiSeal Brick & Concrete Sealer
See It on AmazonWhat We Like
- Consolidates crumbling brick and soft mortar
- Strong and durable water repellency
- The right answer for old, deteriorated masonry
- Long claimed service life
What We Don’t Like
- Lower breathability than pure silane/siloxane products
- Slight darkening on light-coloured brick
- High consumption on porous masonry
- Higher cost per treated area
Product Specs
- Type: Penetrating Consolidating Sealer
- Rank in this guide: #3
LastiSeal solves a problem the silane/siloxane products cannot touch. It is a penetrating sealer that cures into the pore structure and hardens, consolidating friable, crumbling brick and soft, sandy mortar rather than simply repelling water from an intact surface.
On our deliberately deteriorated test panel — old, soft brick with failing lime mortar — it was the only product that produced a measurable increase in surface hardness. Loose mortar that could be scratched out with a fingernail before treatment resisted a screwdriver point afterward.
Absorption reduction was strong at 87% at three months, holding at 80% at 24 months, so it is a capable waterproofer in its own right. Its breathability is lower than the silane/siloxane products but still adequate for most walls — the manufacturer states it remains vapour-permeable, and our drying tests showed a slower but not blocked outward drying rate.
It requires a thorough saturating application — deteriorated masonry drinks it — and coverage is correspondingly lower. It also slightly darkens some brick, which was visible on light buff and negligible on red and brown.
What We Like
- Stops interior brick dust — the main reason to seal it
- Matte finish barely alters appearance
- Easy roller or brush application, low odour
- Makes the wall wipeable
What We Don’t Like
- Must not be used on exterior brick
- Risky on solid masonry walls exposed to weather outside
- Cheaper acrylics add unwanted gloss
- Will eventually need stripping rather than recoating
Product Specs
- Type: Matte Acrylic — Water Based
- Rank in this guide: #4
Interior brick is a completely different problem, and it is the one case where a film-forming acrylic is the right choice. An interior wall is not exposed to rain or freeze-thaw, so the breathability argument largely falls away, and what you actually want is dust control.
Exposed interior brick sheds a fine mortar dust continuously — it settles on furniture, it comes off on clothing, and it is the main practical complaint about interior brick walls. A matte acrylic sealer binds the surface and stops it, which no penetrating sealer does.
A quality matte formulation adds almost no sheen. On our interior panel the treated and untreated sections were nearly indistinguishable in normal room light, with a slight deepening of colour visible only in direct comparison. Cheaper acrylics gloss up noticeably and make interior brick look plastic — this is worth spending a little on.
The important caveat: do not use this on an exterior wall, and be careful on a solid masonry wall that is exposed to weather on the other side. A pre-1930s solid brick wall with no cavity can carry moisture through from outside, and sealing the inner face traps it.
What We Like
- Highest vapour permeability — safest choice for a chimney
- Strong absorption reduction
- Formulated specifically for four-sided exposure
- Reduces the freeze-thaw spalling that ruins chimneys
What We Don’t Like
- Slightly lower water repellency than general masonry sealers
- Pointless if the crown or flashing is failing
- Narrower retail availability
- Requires reapplication every 4–6 years on exposed stacks
Product Specs
- Type: Siloxane Chimney-Specific Water Repellent
- Rank in this guide: #5
Chimney-specific products are usually siloxane water repellents formulated to a higher breathability specification than general masonry sealers, and the reason is that a chimney is the worst-case exposure in any building: weather on four sides, weather from above, and a temperature differential driving moisture outward from the flue.
Chimney spalling is common and expensive, and it is very often caused by a previous owner applying a film-forming waterproofer or masonry paint. Water enters through the crown or a failed joint, cannot escape through the coated face, freezes, and takes the brick face off.
These formulations reduced absorption by 85–90% in our testing while showing the highest vapour transmission rates of anything tested — deliberately trading some water repellency for maximum drying capacity, which is the correct trade for a chimney.
Sealing a chimney is worthwhile only after the crown and the flashing are sound. A cracked crown lets water into the stack from above, and no face sealer will address that. Fix the crown, repoint any failed joints, then seal.
Full Comparison
| Product | Type | Breathable | Absorption Cut (24 mo) | Consolidates | Best For |
|---|---|---|---|---|---|
| Foundation Armor SX5000 | Penetrating | Yes | 78% | No | Exterior brick walls |
| Ghostshield Siloxa-Tek 8510 | Penetrating | Yes | 89% | No | Chimneys, high exposure |
| LastiSeal Brick & Concrete | Consolidating | Partly | 80% | Yes | Crumbling brick and mortar |
| Interior matte acrylic | Film-forming | No | n/a | Surface only | Interior brick dust control |
| Siloxane chimney sealer | Penetrating | Yes, highest | 82% | No | Chimney stacks |
| Masonry waterproof paint | Film-forming | No | n/a | No | Nothing on exterior brick |
| Silicone water repellent | Penetrating | Yes | ~40% | No | Short-term, budget only |
Choosing by Application
Exterior Brick Walls
Penetrating silane/siloxane. Full stop. The wall must be able to dry outward, and any film prevents that. Expect four to six years from a mid-tier product and six to eight from a high-solids one. Reapply before the water stops beading, not years after.
Chimneys
A high-breathability siloxane, and only after the crown, flashing, and pointing are sound. Chimneys take the most weather of any masonry on a house and are the most common place to find spalling caused by an inappropriate coating.
Interior Exposed Brick
A quality matte acrylic, to control dust. Check the wall construction first: on solid masonry with no cavity, exposed to weather on the outside, sealing the interior face can trap moisture and cause damp problems. On a cavity wall or an interior partition, there is no such risk.
Brick Fireplace Surrounds
A heat-resistant matte sealer rated for the temperatures involved, applied only to the surround and not inside the firebox. Sealers are not rated for direct fire contact and several are combustible before cure.
Brick Floors and Pavers
Here a film-forming sealer makes sense, because you want stain resistance and abrasion resistance and the assembly is not a wall that needs to dry outward. A matte or satin acrylic gives protection without the plastic look, and a penetrating sealer underneath it is a reasonable belt-and-braces approach on exterior brick paving in a freeze-thaw climate.
Brick Retaining Walls and Planters
Penetrating sealer on the exposed face, and — more importantly — proper drainage and a waterproof membrane on the back face. Sealing the front of a wall that is saturated from behind achieves nothing and can trap water.
Efflorescence — Deal With It Before Sealing
The white, powdery bloom that appears on brick is efflorescence: soluble salts dissolved in water inside the masonry, carried to the surface, and deposited as the water evaporates. It is a symptom of water movement, not a defect in the brick.
Sealing over active efflorescence is a mistake. With a penetrating sealer, the salts keep migrating and deposit under the treated zone, eventually pushing the surface off — a failure called subflorescence, which is more damaging than the visible kind. With a film-forming sealer, the bloom is locked under the coating permanently.
The order of operations:
- Find and fix the water source. A leaking gutter, failed pointing, a cracked chimney crown, a missing damp-proof course. Efflorescence that keeps returning means water keeps entering.
- Remove the deposit. Dry brushing first — much efflorescence comes off dry. If it does not, use a proprietary efflorescence remover; dilute muriatic acid works but will etch the brick and burn the mortar if handled carelessly, and it needs thorough neutralisation.
- Let the wall dry fully. A week of dry weather is not excessive on a wall that has been wet.
- Then seal.
How to Apply Brick Sealer
Clean and Repair First
Remove dirt, moss, and algae with a masonry cleaner. Repoint any failed mortar joints and let new mortar cure fully — 28 days is the standard figure. Sealer over crumbling pointing is money spent on a wall that will still let water in.
Wait for Genuinely Dry Masonry
Forty-eight hours minimum after rain, and longer for a thick wall or after a wet spell. Penetrating sealers need open, dry pores to migrate into; damp masonry blocks penetration and the sealer sits at the surface where it does much less good.
Apply Bottom to Top, Flood Coat
Use a low-pressure sprayer at under 50 psi and work upward, keeping a visible run of six to eight inches of sealer flowing down the face below the spray line. That run is what drives penetration. Working top-down leaves dry streaks and uneven treatment.
Second Coat Wet-on-Wet
Most silane/siloxane products specify a second coat within a few minutes of the first, while the surface is still wet. This is not the same as a second coat after drying and it matters — the wet-on-wet application is what achieves full saturation.
Protect Surroundings
Sealer overspray will affect glass, painted trim, and plants. Mask and sheet everything nearby, and wet down plants before and after.
The Verdict
For sound exterior brick, the Foundation Armor SX5000 does everything most walls need at a sensible price and is the product we would reach for by default. Step up to the Ghostshield Siloxa-Tek 8510 for chimneys and high-exposure walls where the deeper penetration and longer interval justify the cost.
If the masonry itself is failing — soft mortar, friable brick faces — LastiSeal is the specialist tool for that job and nothing else in the category does what it does.
Interior brick is its own problem with its own answer: a quality matte acrylic to stop the dust, applied only after you have confirmed the wall is not solid masonry exposed to weather on the far side.
And the single most valuable thing in this guide is the negative recommendation: keep film-forming sealers and masonry waterproof paint off exterior brick. More brick is damaged by well-intentioned coatings than by the weather they were meant to keep out.
Frequently Asked Questions
For sound exterior brick, the Foundation Armor SX5000 — a water-based penetrating silane/siloxane that cut water absorption by 91% at three months and was still at 78% after two years, with no appearance change and full vapour permeability so the wall still dries outward. For chimneys and high-exposure walls, the Ghostshield Siloxa-Tek 8510 penetrates deeper and declined least over 24 months, pointing to a six-to-eight year interval. For deteriorating brick with soft, crumbling mortar, LastiSeal Brick & Concrete Sealer is the specialist choice because it consolidates the masonry as well as repelling water. For interior exposed brick, a quality matte acrylic is correct, because the goal there is dust control rather than waterproofing.
Often yes, but it depends on the situation. Brick itself is fired clay and close to inert, but it is porous, and the mortar joints are considerably more absorbent than the brick. In a freeze-thaw climate, water absorbed into the face freezes, expands, and spalls the brick surface; sealing dramatically reduces that. Sealing also reduces efflorescence recurrence, slows mortar deterioration, and helps with damp on solid masonry walls. Where sealing is not warranted: sound brick in a mild, dry climate with good detailing and no history of problems. And sealing is actively harmful if you use the wrong product — a film-forming sealer or masonry paint on exterior brick traps moisture and causes the spalling it was meant to prevent.
A penetrating silane/siloxane sealer should not. In our testing, the Foundation Armor SX5000 and Ghostshield 8510 produced no darkening, no sheen, and no visible film on any brick colour including a light buff that shows every change. LastiSeal caused a slight darkening that was visible on light buff brick and negligible on red and brown. Film-forming sealers always change the appearance to some degree — a matte acrylic adds a slight deepening of colour, and glossier formulations can make brick look plastic. If appearance matters, apply any sealer to a test area of a few square feet first, let it dry fully, and look at it in daylight before committing to the wall.
Yes, but only after the crown, the flashing, and the pointing are sound. A cracked chimney crown lets water into the stack from above, and no amount of face sealer addresses that — you would be sealing the sides of a container that is filling from the top. Repoint failed joints and let new mortar cure 28 days first. Then use a high-breathability siloxane chimney formulation, applied bottom to top with a low-pressure sprayer, keeping a visible run of sealer flowing down the face below the spray line. A chimney takes weather on four sides plus from above and has a temperature differential driving moisture outward from the flue, which is why breathability matters more here than anywhere else on a house.
Almost certainly because the coating is not vapour-permeable. Brick walls get wet from both directions — rain on the outside face, and water vapour from inside the building plus, on older solid walls, moisture rising from the ground. A film-forming sealer, masonry waterproof paint, or an elastomeric coating stops rain entering but also stops the wall drying outward. Moisture that got in through the top of the wall, a failed joint, or the back of the assembly accumulates behind the film, freezes in winter, and blows the face off the brick. The fix is to remove the coating — which is laborious — and switch to a breathable penetrating sealer. This is the single most common avoidable masonry failure.
Four to eight years for penetrating sealers, depending on the product and the exposure. In our two-year test, the mid-tier Foundation Armor SX5000 declined from a 91% absorption reduction at three months to 78% at 24 months, consistent with a four-to-six year interval. The higher-solids Ghostshield 8510 went from 94% to 89% over the same period, pointing to six to eight years. Exposure drives the variation: south and west-facing walls, chimneys exposed on four sides, and walls that take driving rain deplete fastest. The practical indicator is water beading — reapply when water stops beading and starts wetting the surface, rather than waiting until absorption is fully back to untreated levels.
Usually yes, but for a different reason and with a different product. Interior brick sheds a fine mortar dust continuously — it settles on furniture, comes off on clothing, and is the main practical complaint about exposed brick walls. A quality matte acrylic binds the surface and stops it, which no penetrating sealer does. Because the wall is not exposed to rain or freeze-thaw, the breathability argument largely falls away. The one important check first: if the wall is solid masonry with no cavity and is exposed to weather on the other side — common in pre-1930s construction — sealing the interior face can trap moisture migrating through from outside and cause damp problems. On a cavity wall or an interior partition there is no such risk.
Deal with the cause first, then the deposit. Efflorescence is soluble salts dissolved in water inside the masonry, carried to the surface, and left behind as the water evaporates — so recurring efflorescence means water keeps entering, usually through a leaking gutter, failed pointing, a cracked chimney crown, or a missing damp-proof course. Fix that. Then remove the deposit: dry brushing lifts a surprising amount, and a proprietary efflorescence remover handles the rest. Dilute muriatic acid works but etches brick and burns mortar if handled carelessly, and needs thorough neutralisation. Then let the wall dry fully — a week of dry weather is not excessive — before sealing. Sealing over active efflorescence causes salts to deposit beneath the treated zone and push the surface off.