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ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Masonry Sealer:
Brick, Block & Stone
Done Right

Which masonry sealer to use on brick, block, stone and stucco, what the Brick Industry Association says to avoid, and how to prove it worked with a RILEM tube.
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Tell us the wall type, whether it is above or below grade, and where the water shows up. A certified ArmorThane applicator near you will follow up.

  • Foundation and basement walls
  • Retaining walls and planters
  • Seamless spray-applied polyurea
  • Straight answer: sealer or membrane
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Step 1 of 3
10+ yrs
Typical life, silane or siloxane
BIA Technical Note 6A
1 year
Preferred wait on new brickwork
BIA Technical Note 6A
$2–$10
Pro brick waterproofing, per sq ft
HomeGuide, 2026
≤ 20%
RILEM tube drop in 20 min = treated OK
Pecora PEC 170

A masonry sealer is a clear treatment for brick, concrete block, stone, stucco and mortar that keeps rain from soaking into the wall while still letting water vapor out. That last part is what separates a good masonry sealer from a bad one. Seal brick with the wrong product and you trap moisture behind the face, and the next few winters pop the faces off the brick. We build coatings for a living, and our honest advice on above-grade masonry is that most walls want a breathable penetrating water repellent, applied after the real leaks are fixed, not a shiny film.

Quick answer

For exterior brick, block and stone, use a breathable silane, siloxane or silane/siloxane blend. The Brick Industry Association (BIA) says not to put film-forming coatings such as acrylics on brick in freeze-thaw climates, rates silanes and siloxanes at 10+ years of life, and wants cracks, failed sealant and bad mortar joints fixed first. Wait at least a month after a new building is closed in (a year is preferred), test a 10 sq ft area, and expect about $2–$10 per sq ft professionally applied.

What's in this guide
  1. 1Masonry sealer types: penetrants vs films
  2. 2Comparison table with service life
  3. 3Masonry sealer selector (tool)
  4. 4Fix the leak before you seal
  5. 5Coverage and cost calculator (tool)
  6. 6RILEM tube test checker (tool)
  7. 7How to apply masonry sealer
  8. 8When a sealer is the wrong answer
  9. 9Masonry sealer FAQ
Chemistry

Masonry sealer types: penetrants vs. film formers

Every clear masonry sealer does one of two things. Penetrants soak into the pores and line them with a water-repellent molecule; the surface looks the same, and vapor still passes through. Film formers leave a continuous skin on the face. The BIA's Technical Note 6A groups them this way:

Penetrant

Silanes

The smallest molecules, so they go deepest, which matters on dense concrete and brick. BIA lists 10+ years of life. They need some alkalinity and moisture to react, and on very porous block they can pass straight through before they cure.

Penetrant

Siloxanes and blends

Larger molecules that bead water well on porous block and brick. BIA also gives siloxanes 10+ years and specifically suggests a siloxane or preblended siloxane/silane for brick. PROSOCO's Siloxane PD, a typical example, is 4% solids with VOC under 30 g/L.

Penetrant

Silicone resins and siliconates

Older, cheaper chemistry. BIA notes silicone resins typically last about one year. Siliconates react with the masonry and can leave white residue if over-applied. Fine for a quick fix, not our first pick.

Film former

Acrylics, urethanes, stearates

Give you sheen and color enhancement, and acrylics can last 5–7 years per BIA, but they reduce how well the wall breathes. BIA's rule is blunt: do not apply film-forming coatings to brickwork in freeze-thaw environments. They belong on stone caps, interior brick or warm-climate features, if anywhere.

Breathability is not optionalExcept for anti-graffiti work, BIA says to use only breathable coatings with a water vapor permeability of 0.98 or greater measured by ASTM E96. CMHA's TEK 19-01 makes the same point for concrete block: films can reduce the vapor transmission of the wall, and humidity inside the wall has to be able to escape.
Compare

Masonry sealer comparison by life and breathability

Service life figures are the BIA's typical values; your result depends on exposure, coverage rate and how well the wall was prepared. Click any heading to sort.

Sealer typeFamilyTypical life, yrsBreathableFreeze-thaw brickChanges lookBest use
SilanePenetrant10+YesSuitableNoDense brick, concrete, precast
Siloxane / silane-siloxane blendPenetrant10+YesSuitable (BIA preferred)NoBrick, block, stone, stucco
Silicone resinPenetrantAbout 1MostlyShort-livedNoTemporary treatment
AcrylicFilm former5–7ReducedNot recommendedSheen, darkensInterior brick, warm-climate stone
UrethaneFilm former1–3ReducedNot recommendedSheenInterior, anti-graffiti
Source: Brick Industry Association Technical Note 6A, Colorless Coatings for Brick Masonry; CMHA TEK 19-01. Freeze-thaw column reflects BIA's guidance against film formers on exterior brick in freeze-thaw climates.
Tool 1

Which masonry sealer fits your wall?

Tell the selector what the wall is made of, how old it is and what it looks like now. It returns a sealer family, whether to wait, and what to fix first, following BIA Technical Note 6A and CMHA TEK 19-01.

Selector

Masonry sealer selector

Applies the BIA and CMHA rules: penetrants for exterior walls, no films on freeze-thaw brick, repairs before sealing, and minimum wait times on new work.

What you see now
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When to apply
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Typical life (BIA)
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Before you buy

A masonry sealer will not fix a leaking wall

This is the part most product labels skip. A clear water repellent reduces how much rain the face of the masonry absorbs. It does not close cracks, it does not replace missing mortar, and it does nothing about failed flashing or a bad window joint. CMHA says plainly that penetrating repellents do not bridge cracks or voids, so those must be repaired first. BIA's list of corrections before coating includes:

  • Replacing failed sealant at windows, doors and control joints.
  • Repointing cracked or crumbling mortar joints. HomeGuide puts repointing at $3–$20 per sq ft and tuckpointing at $5–$25 per sq ft in 2026.
  • Replacing brick with spalled faces.
  • Surface-grouting hairline separations between brick and mortar.

Then think about where the water is actually coming from. Wet spots under windows usually mean sills or flashing. A damp band at the base of a wall is often splash-back or ground moisture, which a wall sealer will not stop. If the leak is through a basement or retaining wall pushing against soil, you need a waterproofing system, not a sealer.

Flaking brick?If brick faces are already spalling, stop and find the moisture source. Sealing a wall that is wet from behind can make spalling worse, because the water now leaves the wall more slowly.
Tool 2

Masonry sealer coverage and cost calculator

Masonry drinks sealer at very different rates. PROSOCO's data sheets put fired clay brick at 50–175 sq ft per gallon for Siloxane PD and split-face block as low as 30–100 sq ft per gallon for its Blok-Guard WB 15 silicone emulsion, which also calls for two wet-on-wet applications on block. Measure the wall, subtract windows and doors, and the calculator does the rest.

Calculator

Gallons and cost for a masonry wall

Net area = length × height − openings. Gallons = net area × applications ÷ published coverage (low and high). Pro cost uses HomeGuide's $2–$10 per sq ft range for brick waterproofing.

Perimeter for a whole house
A door is about 20, a window 15
From your supplier
Block: 2 wet-on-wet
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Net wall area
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Gallons needed
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DIY material cost
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Professional range

Tool 3

Did the sealer work? The RILEM tube test

A RILEM tube (also called a Karsten tube) is a small graduated glass or plastic tube you putty to the wall, fill with water and time. BIA describes the tube as graduated from 0 to 5 mL over a contact area under 1 sq in., and recommends it for before-and-after comparisons only, not as a pass/fail rating of the whole wall: a big drop in absorption after treatment tells you the repellent went on at the right rate. Sealant maker Pecora's procedure PEC 170 reads the tube after 20 minutes and calls performance acceptable when the water level drops no more than 20% of the original height, which on a 5 mL tube means 1.0 mL or less absorbed.

Checker

RILEM tube result checker

Enter the mL absorbed at 20 minutes on an untreated spot and a treated spot (same wall, same exposure). Reduction = (untreated − treated) ÷ untreated. Pass mark per Pecora PEC 170: treated absorption ≤ 20% of a 5 mL column.

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Absorption reduction
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Treated drop, % of 5 mL
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Treated rate, mL/hr

Test more than one spotRILEM readings vary a lot from brick to brick and joint to joint. BIA cites a University of Wyoming study that needed 56 tube tests on a 12 sq ft specimen to get the sampling error down to 50%. Run several tubes on brick faces and on mortar, and compare averages.
Application

How to apply masonry sealer the way the data sheets intend

  1. Repair, then wait

    Do the repointing, sealant and brick replacement first. On new brickwork BIA wants at least one month after close-in and prefers a year, so early efflorescence is not sealed in. PROSOCO lists new concrete at 14–28 days before Siloxane PD.

  2. Clean and let it dry

    Remove dirt, efflorescence and mortar smears with a cleaner made for the substrate. CMHA calls for 3 to 5 days of drying after cleaning or rain before applying a repellent.

  3. Check the weather window

    CMHA says temperatures should stay above 40°F for two to four days after application; PROSOCO's range is 40–95°F during use and for 8 hours after, with 6 hours of rain protection.

  4. Do a test area

    BIA asks for test areas of at least 10 sq ft. Check for darkening, residue and absorption with a RILEM tube after the repellent has cured; PROSOCO says full repellency takes about 72 hours.

  5. Flood, bottom up

    Low-pressure spray under 50 psi, working from the bottom up and saturating until you get a 4–8 in. rundown, per PROSOCO. Let it soak in 5–10 minutes and resaturate. Protect glass, plants and painted trim.

  6. Verify and record

    Re-test with RILEM tubes at the same spots, note the date and product, and reapply when water stops beading. With silanes and siloxanes that is usually measured in years, not seasons.

Honest limits

When a masonry sealer is the wrong product

We make polyurea and polyurethane coatings, and we would rather you put a few gallons of siloxane on a brick facade than sell you a coating it does not need. A clear repellent is the right tool for above-grade walls that get wet from rain. It is the wrong tool for these jobs:

Not a sealer job

Basement and foundation walls

Water pushed through by soil and hydrostatic pressure needs a membrane on the positive side. See foundation waterproofing and basement waterproofing.

Not a sealer job

Retaining walls and planters

Soil sits against the masonry permanently. A seamless membrane, such as a spray-applied polyurea, works where a repellent cannot; see retaining wall waterproofing.

Different product

Walkways, patios, caps

Horizontal masonry sees standing water, salt and wear. Pavers want a paver sealer; poured slabs want a concrete sealer rated for traffic.

Opaque option

Block you want to paint anyway

If you plan to change the color of a block wall, a breathable masonry coating or waterproof paint does both jobs. Painting brick is a one-way door, so think twice. Stucco often does better with an elastomeric coating.

Below-grade or retaining walls?

When a sealer won't hold the water, a membrane will.

Certified ArmorThane applicators spray seamless polyurea membranes on foundations, retaining walls and planters. Tell us what is leaking and we will tell you honestly whether you need us or a gallon of siloxane.

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FAQ

Masonry sealer questions

What is the best masonry sealer for brick?

For exterior brick, a breathable siloxane or silane/siloxane blend. The Brick Industry Association recommends considering a siloxane or preblended siloxane/silane and rates both chemistries at 10+ years of typical life. Avoid film-forming acrylics on brick in freeze-thaw climates.

Should you seal brick at all?

Not always. Well-built brick walls are designed as drainage walls and often do fine untreated. Seal when the face absorbs enough water to cause damp interiors, heavy efflorescence or freeze-thaw damage, and only after cracks, mortar joints and sealant are repaired.

How long should new brick cure before sealing?

BIA says at least one month after the building is closed in, and prefers a full year so that early efflorescence comes out before a repellent is applied.

Does masonry sealer make brick waterproof?

No. It makes the face water repellent. It will not stop water through cracks, open joints or flashing defects, and it will not resist water pushed through by soil pressure. Those need repairs or a waterproofing membrane.

How much does it cost to seal a brick house?

HomeGuide's 2026 range for waterproofing brickwork is $2 to $10 per square foot. Materials alone are a small part of that; most of the cost is access, masking, cleaning and repairs.

Will masonry sealer change the color of my brick?

Penetrating silanes and siloxanes generally do not change appearance when applied at the right rate. Film formers and wet-look products darken and add sheen. Always do a 10 sq ft test area, as BIA recommends, and look at it dry.

Can I use masonry sealer on concrete block?

Yes, but pick a product rated for block. Some siloxanes are not recommended for CMU, and block is so porous that PROSOCO's Blok-Guard WB 15 covers only 30–100 sq ft per gallon and calls for two wet-on-wet applications.

How do I know when to reseal?

Spray water on the wall. If it beads and runs off, the repellent is working. If it darkens the masonry and soaks in, compare a RILEM tube reading against your original record and reapply when absorption has climbed back toward untreated levels.

AT
Written by the ArmorThane technical team. We have manufactured polyurea, polyurethane and polyaspartic coatings in Springfield, Missouri since 1989 and train certified applicators across North America. Technical guidance here follows the BIA and CMHA documents and manufacturer data sheets listed below. Updated October 2026.

Sources

  1. Brick Industry Association, Technical Note 6A, Colorless Coatings for Brick Masonry: gobrick.com/media/file/6a-colorless-coatings-for-brick-masonry.pdf
  2. Brick Industry Association, RILEM Tube Testing and Brick Masonry: gobrick.com/media/file/bb-rilem-tube-testing_final.pdf
  3. CMHA TEK 19-01, Water Repellents for Concrete Masonry Walls: cmha.org/resource/tek-19-01
  4. Pecora PEC 170, RILEM Tube Test Procedure for Penetrating Water Repellents: pecora.com/.../PEC-170-RILEM-Tube-Test-Procedure.pdf
  5. PROSOCO Siloxane PD product data sheet: dciflooring.com/.../Prosoco_WeatherSeal_Siloxane_PD_PDS.pdf
  6. PROSOCO Siloxane PD product page: prosoco.com/product/siloxane-pd
  7. PROSOCO Blok-Guard & Graffiti Control WB 15 data sheet: prosoco.com/.../WS_BGGC_WB_15_PDS.pdf
  8. HomeGuide, brick and masonry repair cost (2026): homeguide.com/costs/repair-brick-masonry-work-cost

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