Masonry Waterproofing: Water Repellents, Efflorescence and Rising Damp

Masonry waterproofing keeps rain and ground moisture out of above-grade brick, block and stone walls through repairs and clear water repellents that line the pores without sealing in vapor. Penetrating water repellents seldom stop water through cracks wider than 0.5 mm (0.02 in), per BIA Technical Note 6A (August 2008), so water that enters through joints, flashings and cracks needs a repair before any treatment. Which repair and which treatment does a wall need?

The answer runs through 5 product groups in job order: repairs to mortar joints, sealant joints and flashings; penetrating silane and siloxane repellents; film-forming clear sealers; opaque wall coatings and renders; and chemical damp-proof courses, with the face treatment sold in the UK as masonry protection cream. Efflorescence and rising damp have their own pages. Masonry is one application of construction chemicals where the wall, the climate and the source of the water set the system.

Standards, codes and regulations are checked against their issuing bodies, product values against the named data sheet and prices against the dated source named in the sentence; see our methodology and fact-checking.

What Is Masonry Waterproofing?#

Masonry waterproofing is the set of repairs and surface treatments, chiefly clear penetrating water repellents, that reduce how much rain a brick, block or stone wall absorbs while still letting the wall dry out as vapor. BIA Technical Note 6A (August 2008) calls the clear products colorless coatings and splits them into two groups by how they work.

The two groups of clear masonry water repellents, and the forms they come in, are listed below.

• Penetrants: siloxanes, silanes, methyl siliconates, silicone resins and RTV silicone rubber.
• Film formers: acrylics, stearates, mineral gum waxes and urethanes.
• Forms: water-borne emulsions, solvent-borne solutions, and creams or gels.

Water Repellent, Sealer or Waterproofer: What the Labels Mean#

Masonry sealer, brick sealer, block sealer and clear water repellent are trade names for the same product family, and the label says nothing about whether a product penetrates or forms a film. The data sheet names the chemistry, and the chemistry decides vapor transmission, service life and where the product fits.

European standards use another word for concrete: EN 1504-2:2004 calls a pore-lining treatment a hydrophobic impregnation (H). A pigmented product labeled as a waterproofer or masonry paint is a film former. Concrete sealers for floors, slabs and driveways form a separate group, compared under concrete sealers.

How Does Water Get Into Brick, Block and Stone Walls?#

Water gets into above-grade masonry in three ways: wind-driven rain through cracks, open mortar joints and failed flashings, absorption through the face of porous units, and capillary rise from the ground, and a repellent addresses only the second. Each path has its own fix, and a treatment chosen before the path is found treats the wrong one.

Wind-Driven Rain, Cracks and Open Mortar Joints#

Rain leaks through brick walls at defects, not through sound brick: penetrating water repellents seldom stop water through cracks wider than 0.5 mm (0.02 in) or through incompletely filled joints (BIA Technical Note 6A, August 2008). Defects include cracked or open bed and head joints, cracks through units, and gaps at copings, sills, windows and flashings.

Copings, flashings and sealant joints come before any treatment, because a repellent neither bridges a gap nor carries out water that a flashing drains.

Salt Deposits on the Face as a Symptom of Water Entry#

White salt deposits on a wall are water made visible: soluble sulfates and carbonates of sodium, potassium, calcium, magnesium and aluminum travel with moisture and stay behind when it evaporates (BIA Technical Note 23A, June 2019). Chlorides come from calcium chloride accelerators, seawater or hydrochloric acid cleaning. Deposits grow through winter and decrease in spring, according to a Sika technical bulletin on efflorescence.

Cryptoflorescence forms 3 to 6 mm (1/8 to 1/4 in) below the surface behind low-permeability coatings and spalls the face (BIA Technical Note 23A). A breathable repellent goes on only after the salts are cleaned off and the water source is stopped, and never as the sole treatment.

Capillary Rise at the Base of the Wall#

Ground moisture that climbs a wall without a working damp-proof course is treated by injecting a water repellent into a mortar course, not by coating the face. The repellent diffuses through the damp wall and cures to a horizontal hydrophobic barrier against capillary rise. The Property Care Association groups the methods as hand insertion of thixotropic creams (the most common), low-pressure injection, gravity feed and high-pressure injection.

Diagnosis comes first, because tide marks and moisture-meter readings alone mislead, and hygroscopic salts in plaster absorb moisture from the air above about 75 % RH. In the UK, BS 6576:2005+A1:2012 is the code of practice for diagnosing rising damp and installing chemical damp-proof courses, and it excludes walls under water pressure, which fall under BS 8102.

Masonry Waterproofing Systems Component by Component#

A masonry waterproofing system runs in job sequence: repoint open joints, replace failed sealant and flashings, clean off salts, then apply a vapor-open penetrating repellent, or an opaque coating or render where the wall needs crack bridging. A chemical damp-proof course is added only where water rises from the ground. What can you seal bricks with? Sound brick takes a silane or siloxane repellent, and cracked or open-textured walls take an elastomeric coating or a render.

The table below compares the 8 steps of a masonry system in job order, with the document that governs each step and its limit.

Repairs Before Any Treatment: Mortar Joints, Sealant Joints and Flashings#

Repointing, joint sealing and flashing repair come before any repellent, and BIA advises waiting several months after repairs before deciding whether a treatment is still needed.

Repointing mortar is softer and more permeable than the units and no harder than the historic mortar (NPS Preservation Brief 2, October 1998). Preservation Brief 2 rakes joints to 2 to 2.5 times the joint width and gives approximate strengths from 17.2 MPa (2,500 psi) for type M down to 2.4 MPa (350 psi) for type O, the types that ASTM C270-26 specifies by proportion or property. What is a good waterproof sealant for masonry? At copings, openings and movement joints, it is an elastomeric joint sealant to ASTM C920-18(2024); a sealant seals the joint, not the face.

Penetrating Silane and Siloxane Repellents#

Penetrating repellents line the pores of brick, block and stone and turn capillary suction into repellency without filling the pores, so the wall stays vapor-open.

BIA Technical Note 6A gives penetration of up to 10 mm (3/8 in) and solids of 5 to 40 % by weight, with siloxanes at 5 to 12 % and silanes at 20 % or more. Silanes and some siloxanes tolerate slightly damp substrates, and silanes and siloxanes bond to unprotected glass, so windows are masked before application. Three limits apply: efficiency is reduced on pure limestone, siliconates are not alkali resistant and fail on concrete, and salts can crystallize behind the treated zone on salt-loaded masonry. The chemistry of silanes and siloxanes is set out on its material page.

Film-Forming Clear Sealers and Masonry Paints#

Film formers such as acrylics, urethanes, stearates and mineral gum waxes leave a surface layer that bridges hairline cracks but cuts vapor transmission and can trap salts and moisture behind it. Acrylics need thoroughly dry substrates, and film formers cloud when applied to damp walls.

BIA advises against film formers in freeze-thaw climates. A paint sealer for concrete block is a pigmented film former, judged by the same vapor and salt limits as a clear film, with its vapor transmission measured to ASTM E96.

Opaque Wall Coatings and Renders Over Masonry#

Where a block or stucco wall has hairline cracks, an elastomeric wall coating, a high-build film with a low glass transition that stays rubbery, bridges them while remaining vapor-permeable. IIBEC guidance puts the glass transition of the class at about -40 to -10 °C (-40 to 14 °F) and classes a film below 1.0 perm as a vapor retarder rather than a breathing coating. ASTM D6904-03(2022) wets coated block under water spray and air pressure equal to a 158 km/h (98 mph) wind for a recommended 24 hours and sets no pass/fail value. Renovation render (type R to EN 998-1:2016) is the type for damp, salt-loaded masonry, where salts crystallize behind a dense render. IBC 2021 Section 2512 calls for two plaster coats over masonry or concrete, with application covered by ASTM C926-26.

How to Choose a Masonry Waterproofing System#

The right masonry waterproofing system follows the wall: the unit, the climate, the condition of joints and cracks, and whether salts or rising moisture are present, and a specification should name the test criteria, not a brand. Cracks wider than 0.5 mm (0.02 in) should be repaired before any product is chosen.

The table below matches 8 wall conditions with the first fix, the treatment and what to avoid.

Clay Brick, Concrete Block and Natural Stone#

Clay brick and natural stone take a clear penetrating repellent when joints are sound, while open-textured concrete block can need an opaque elastomeric coating because its pores and hairline cracks exceed what a repellent bridges. Brick drainage walls in new construction need no coating at all, according to BIA Technical Note 6A.

Natural stone should get a trial area first, since penetrant efficiency is reduced on pure limestone. Concrete block should not receive a siliconate, which is not alkali resistant.

Freeze-Thaw Climates, Historic Walls and Salt-Loaded Masonry#

In freeze-thaw climates, on historic walls and on salt-loaded masonry, the treatment should stay vapor-open, because water and salts trapped behind a film crystallize or freeze below the face. Historic walls should be repointed with lime mortar no harder than the original, per NPS Preservation Brief 2 (October 1998), before any repellent is considered.

On salt-loaded masonry, salts crystallize behind a treated zone as well as behind a film, so the salt source should be stopped first. A renovation render to EN 998-1:2016 type R, or a chemical damp-proof course where moisture rises from the ground, deals with the cause, while a dense film or render on top traps it.

Masonry Water Repellent Standards: EN 1504-2:2004, BIA Technical Note 6A and SCAQMD Rule 1113#

Three documents judge masonry water repellents: EN 1504-2:2004 classes hydrophobic impregnations for concrete, BIA Technical Note 6A (August 2008) recommends US criteria for brick, and SCAQMD Rule 1113 sets criteria for reactive penetrating sealers. The first is a standard requirement, the second an industry recommendation and the third a condition of a VOC category.

The table lists each threshold with what it governs and the edition it comes from.

EN 1504-2 Hydrophobic Impregnation Classes#

EN 1504-2:2004 sorts hydrophobic impregnations into Class I with a penetration depth below 10 mm (0.39 in) and Class II at 10 mm or more. The same table sets an absorption ratio below 7.5 % of the untreated value, and below 10 % after alkali immersion, measured to EN 13580. The drying rate coefficient exceeds 30 % for Class I and 10 % for Class II (EN 13579).

A freeze-thaw-salt test to EN 13581 applies only where de-icing salts are used, and it requires mass loss to start at least 20 cycles later than on untreated concrete. The standard is written for concrete, so a masonry specification borrows its classes rather than citing it as a masonry product standard. Protection principles and the other two EN 1504-2 product types, impregnation and coating, are covered under EN 1504-2.

US Performance Criteria From BIA Technical Note 6A#

BIA Technical Note 6A recommends that a clear repellent cut the maximum leakage rate of three ASTM E514 test panels by 90 % and the damp area and collected water at 24 hours by 75 % against untreated panels. In the field, the note asks for at least 75 % less water loss in an ASTM C1601 test. In the lab, it allows no more than 10 % loss of vapor transmission by the ASTM E96 desiccant method.

These figures are industry recommendations, not code requirements, so a specification that wants them names them. The note prints the field method once as "C1602"; the method is ASTM C1601-22a.

How Is Water Penetration Through Masonry Tested? ASTM E514, ASTM C1601 and the RILEM Tube#

Water penetration through masonry is tested in three ways: ASTM E514/E514M-20 measures leakage through laboratory wall panels, ASTM C1601-22a measures surface water penetration on site, and the RILEM tube (Test II.4, 1980) measures absorption with no pass/fail value. Each test answers a different question. The pass values belong to BIA, not to ASTM or RILEM.

The table lists the five tests that apply to masonry treatments, where each runs and who owns the pass value.

Laboratory Wall Panels Under ASTM E514/E514M-20#

ASTM E514/E514M-20 builds wall panels, wets them with a water spray under air pressure and records leakage, damp area and collected water through the wall. The current edition is active and was last updated on 2020-12-22 by ASTM subcommittee C15.04.

The E514-09 edition's conditions are a chamber pressure of 500 Pa (10.4 psf), equal to a wind of about 28.5 m/s (64 mph), and a spray rate of 138 L/(m²·h) (3.4 gal/(ft²·h)). Pressure affects the results, so treated and untreated panels are compared under identical conditions.

Field Tests: The ASTM C1601-22a Chamber and the RILEM Tube#

ASTM C1601-22a measures water penetration of an existing masonry wall surface on site, and it is the field method behind BIA's 75 % criterion. First published in 2008, the method was last updated on 2022-06-20.

The RILEM tube, also called the Karsten tube, is a graduated tube sealed to the face and filled with water. The current tube reads 0 to 5 mL at a water head of about 120 mm (4.72 in); the 0 mL mark equals a wind of about 158 km/h (98 mph) and the 5 mL mark about 72 km/h (45 mph). Readings are taken at 5, 10, 15, 30 and 60 minutes. RILEM Test II.4 (1980) sets no pass/fail value and has no ASTM equivalent, and ASTM work item WK27132 proposes one. Its use is comparative: the same spots on a trial area, before and after treatment.

VOC and Safety Rules for Masonry Water Repellents#

VOC limits for masonry water repellents run from 100 g/L (0.83 lb/gal) for waterproofing concrete and masonry sealers in the South Coast air district to 600 g/L (5.01 lb/gal) for waterproofing sealers under the federal EPA rule. Solvent-borne silanes add flammability and skin-irritation rules on site. Limits attach to the product category and the place of sale, so one product can face 100, 400 or 600 g/L depending on where it is sold.

VOC Limits by Category and Jurisdiction#

The South Coast AQMD caps waterproofing concrete and masonry sealers at 100 g/L (0.83 lb/gal) under Rule 1113 (amended 2016-02-05) and allows reactive penetrating sealers 350 g/L (2.92 lb/gal) only for restricted uses. The restricted uses are reinforced concrete bridges within 8 km (5 mi) of the coast or above 1,219 m (4,000 ft), and registered historic buildings. The product must also show at least 80 % water repellency improvement by the rule's test methods and stay vapor-open to ASTM E96.

The table lists the VOC limits that apply to masonry water repellents in North America, by instrument, category and date.

A Proposed Amended Rule 1113 was still with its working group as of 2026-10-22, so every South Coast value here carries its 2016-02-05 amendment date. VOC limits for construction chemicals in the other categories, from curing compounds to roof coatings, are listed under VOC limits for construction chemicals.

Silane, Siloxane, Siliconate and Silica Rules for Applicators#

Isobutyltriethoxysilane carries a harmonized CLP classification of H315 (Annex VI index 014-007-00-1), octyltriethoxysilane has no Annex VI entry with a notified H315, and solvent-borne silane and siloxane products are flammable. The classification line reads: Isobutyltriethoxysilane: Harmonised CLP Annex VI (index 014-007-00-1): H315; octyltriethoxysilane: No Annex VI entry; ECHA C&L notified: H315. Hydrolysis of these ethoxysilanes releases ethanol, and methyl siliconates are alkaline; for any product, see the product SDS.

In the EU, the silanes themselves are not listed in REACH Annex XVII, but residual D4, D5 and D6 cyclic siloxanes, on the Candidate List since 2018-06-27, fall under entry 70 as replaced by Regulation (EU) 2024/1328. After 2026-06-06 they may not be placed on the market at 0.1 % w/w or more each, with derogations of up to 1 % each for silicone-polymer residues in adhesion, sealing, gluing and casting uses, and D4 at 0.5 % or D5 and D6 at 0.3 % in protective coatings. On US sites, raking out mortar joints before repointing creates respirable crystalline silica dust, regulated by OSHA 29 CFR 1926.1153 with a PEL of 50 µg/m³ as an 8-hour TWA and an action level of 25 µg/m³, effective 2016-06-23.

How Masonry Waterproofing Work Is Bought: Survey, Trial Area and Scope#

Masonry waterproofing is bought in three steps: a survey that finds where water enters, a trial area tested before and after treatment, and a written scope that lists repairs, cleaning, product, test criteria and access. BIA recommends contractors with at least five years' experience with the selected product.

The trial area is tested with a RILEM tube or an ASTM C1601-22a chamber before and after treatment, at the same spots, and the scope can name BIA's 75 % field reduction as its acceptance figure. The 6 items of a written scope are listed below.

1. Survey: water entry points, crack widths against 0.5 mm (0.02 in), joint condition, salts and any rising moisture.
2. Repairs: repointing with the mortar type, sealant joints, copings and flashings.
3. Cleaning: salt and dirt removal, then a drying period before treatment.
4. Product: chemistry, solids content and VOC category for the place of sale.
5. Test criteria: E514, C1601 or RILEM readings before and after treatment.
6. Access: scaffold or lifts, and masking of glass and adjacent surfaces.

No dated public price for repellent application exists, so quotes price the wall area in m² (ft²), the access, the repairs and cleaning, the number of coats and the trial testing as separate lines. Repointing is priced on its own, per m² (ft²) of wall.

What Is the Best Waterproofing for Masonry?#

No single product is the best waterproofing for masonry: a vapor-open penetrating repellent suits sound, well-jointed brick and stone, an elastomeric coating suits cracked block, and repairs come first on every wall.

The same rule of cause first runs through construction chemicals by application for every other structure, covered under construction chemicals by application.

The 6 sibling application hubs are listed below.

• roof waterproofing: flat roofs and terraces
• parking structure waterproofing: decks and traffic coatings
• bridges, tunnels and marine structures: waterproofing, repair and protection
• water-retaining structures: tanks, reservoirs and pools
• concrete crack repair: crack types, causes and repair methods
• concrete spalling: rebar corrosion and repair

Is sealing brick a good idea?#

Sealing brick is a good idea only after the joints, flashings and cracks are repaired, and only with a vapor-open product; a film over a damp or salt-loaded wall traps both.

What is the best sealer for a concrete block wall?#

Above grade, a concrete block wall takes either a penetrating silane or siloxane repellent or, where hairline cracks and open texture let water through, an elastomeric wall coating; below grade under water pressure, neither is the answer. Below-grade block walls need a waterproofing membrane system, named in the last row of the systems table.

Can you seal brickwork with PVA?#

No: PVA is a bonding agent whose film re-emulsifies when wet, so it is limited to interior dry service and does not repel rain. The film also hydrolyzes in alkaline moisture, and its standards, ASTM C932-06(2024) and C631-09(2020), cover bonding compounds for plaster, set out under PVA bonding agents.

How long does a masonry water repellent last?#

BIA Technical Note 6A gives 10 years or more for silanes and siloxanes, 5 to 10 for RTV silicone, 5 to 7 for acrylics, 1 to 3 for urethanes and about 1 year for stearates and silicone resins. These are service lives by chemistry, not product warranties.

Does a water repellent stop a leaking brick wall?#

No: a water repellent reduces absorption through the face but seldom stops water through cracks wider than 0.5 mm (0.02 in) or through open joints, which are repaired first.