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Cromar Exterior Water Seal is a clear, solvent-based water repellent treatment formulated to provide high-performance protection against moisture ingress on exterior porous surfaces.
Ready to use and designed for ease of application, it is suitable for use on brickwork, concrete, natural stone, paving slabs, asbestos cement and preservative-treated external timber. The product penetrates deeply into porous substrates, forming an effective barrier that repels water while allowing the surface to breathe.
Cromar Exterior Water Seal is not suitable for overpainting and should be considered a final protective finish.
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✔️ Solvent-based formula penetrates deeply to form an invisible water-repellent barrier without changing appearance.
✔️ Helps prevent moss, efflorescence, frost damage, spalling, and unsightly staining on porous surfaces.
✔️ Allows water vapour to escape while repelling rainwater, preserving breathability of treated materials.
✔️ Enhances thermal insulation and prolongs lifespan of exterior walls, paving, and stonework.
✔️ Ready to use with no dilution required, ideal for clean, dry, and absorbent masonry or timber surfaces.
Cromar Exterior Water Seal is a high-performance, solvent-based water repellent developed to safeguard exterior building materials from moisture ingress while preserving their natural appearance. Engineered for deep substrate penetration, this hydrophobic treatment forms an invisible yet effective barrier against water absorption, making it ideal for use on traditional brickwork, sandstone, concrete, paving, and other porous surfaces. Its ability to maintain the original aesthetic of the substrate while delivering robust protection makes it a preferred choice for both heritage buildings and modern constructions.
The formulation penetrates rapidly into porous materials, delivering long-lasting water repellency that helps prevent a host of common moisture-related issues. These include efflorescence, frost damage, surface spalling, biological growth such as moss and algae, and discolouration caused by persistent damp. By reducing the uptake of rainwater and environmental moisture, Cromar Exterior Water Seal not only preserves surface integrity but also supports better thermal performance by reducing damp-induced heat loss through walls.
Unlike surface films that can trap moisture and cause deterioration beneath the surface, Cromar Exterior Water Seal allows vapour to escape while actively repelling liquid water. This breathable formulation ensures that the treated surface remains dry and structurally sound without risking internal condensation or blistering. Its performance makes it especially suitable for use in damp-prone environments where materials must remain both protected and vapour-permeable.
Cromar Exterior Water Seal is suitable for a wide range of exterior applications, including domestic garden walls, patio paving, brick façades, and commercial masonry surfaces exposed to the elements. It is also compatible with preservative-treated timber, offering an additional moisture-repelling layer that contributes to the extended durability of wood in outdoor environments. However, due to its hydrophobic nature, the treatment is not intended for surfaces that require further finishing with decorative paints or renders, as these will not adhere properly.
Supplied in a convenient, ready-to-use formulation, Cromar Exterior Water Seal requires no dilution and delivers consistent results when applied to properly prepared surfaces. Its ease of application makes it suitable for professional contractors and maintenance teams as well as DIY users seeking dependable water repellence with minimal effort. Once cured, the treatment leaves no visible sheen or residue, ensuring a clean, natural finish that enhances and preserves the building’s original look.
By delivering effective moisture control without altering surface appearance, Cromar Exterior Water Seal provides a reliable long-term solution for the protection of exterior masonry and timber. Its low-maintenance benefits and resistance to environmental wear make it a practical investment for property preservation, contributing to the structural health, aesthetic value, and longevity of buildings across a broad spectrum of applications.
Deep Penetrating Water Repellence: Formulated to soak deeply into porous surfaces, the product forms an invisible barrier that repels water and prevents moisture absorption while allowing the surface to breathe naturally.
Suitable for Multiple Substrates: Cromar Exterior Water Seal is compatible with a broad range of external materials including brick, concrete, stone, asbestos cement, paving and preservative-treated timber, offering versatile use across domestic and commercial properties.
Solvent-Based for Superior Durability: Its solvent-based composition ensures better penetration, faster drying and longer-lasting protection compared to water-based equivalents, particularly in exposed conditions.
Invisible Finish: The clear formulation means it does not alter the colour or texture of the treated surface, making it ideal for preserving the original look of bricks, natural stone and decorative masonry.
Helps Prevent Frost and Damp Damage: By stopping water from entering the substrate, the product reduces the risk of frost-related expansion damage and the formation of moss, algae and stains caused by damp conditions.
Ready to Use – No Dilution Required: The product is supplied in its final form, eliminating the need for mixing or dilution on site, which reduces preparation time and ensures consistent performance.
Cannot Be Overpainted: As it forms a hydrophobic surface, Cromar Exterior Water Seal is designed to be used as a final treatment layer only and will not accept decorative coatings applied on top.
Brickwork and Masonry: Ideal for treating exposed facing bricks and blockwork on external walls, helping to reduce water ingress and preserve structural integrity while retaining a natural appearance.
Natural Stone and Concrete: Used to protect sandstone, limestone, granite, and concrete paving slabs from staining and erosion due to water absorption, making it suitable for patios, pathways and driveways.
Asbestos Cement: Provides water resistance to asbestos cement sheets commonly used in older roofing and cladding, helping to minimise moisture retention and associated degradation.
External Paving and Patios: Effectively reduces algae and moss growth on paving surfaces by preventing water accumulation, improving both the appearance and safety of outdoor surfaces.
Preservative-Treated Timber: Enhances water repellence on external wood surfaces such as garden fences, gates and outbuildings that have already been treated with a timber preservative, increasing their lifespan.
Garden Walls and Boundary Structures: Protects decorative and structural garden walls from water-related deterioration while maintaining their natural appearance and finish.
When applying Cromar Exterior Water Seal, appropriate personal protective equipment should be worn at all times. This includes gloves, eye protection, and suitable workwear to prevent skin and eye contact.
The application should take place in a well-ventilated area, and care must be taken to avoid inhalation of any vapour or spray mist. Do not smoke, eat, or drink during application. Ensure that windows, glazed surfaces, painted joinery, and any decorative features that may be sensitive to solvents are masked off prior to application.
Should any splashes occur on glass or unsuitable surfaces, these must be wiped away immediately using white spirit. Always read the product label and refer to the safety data sheet before use.
Cromar Exterior Water Seal is suitable for application to a variety of external porous surfaces, including brickwork, stone, concrete, paving, asbestos cement and preservative-treated timber.
It is important to note that this product is designed solely for materials suitable for external exposure. It should not be used on internal surfaces or on materials that are not designed for external applications. Surfaces that are painted or sealed with non-breathable coatings may prevent absorption of the treatment and compromise its effectiveness.
Before applying Cromar Exterior Water Seal, all surfaces must be completely dry and free from dirt, dust, oil, grease, algae, lichen, moss, or other organic contamination.
Where necessary, surfaces may be washed down using clean water; however, no detergents, soaps, or cleaning chemicals should be used as residues may interfere with penetration. It is essential to allow the substrate to dry thoroughly after washing. Do not apply this product for at least two to three days following rainfall.
Any damaged or defective mortar should be cut out and repointed using a suitable mix prior to treatment. Ensure joints and cracks are sound to prevent water ingress behind treated surfaces.
Cromar Exterior Water Seal is supplied ready to use and must not be diluted. Shake the container well before and during use to ensure even distribution of active ingredients.
The product should be applied generously using either a soft-bristled brush or low-pressure airless spray equipment with a coarse nozzle, ensuring a continuous, even application without atomisation or misting. On vertical surfaces, begin application at the top and work downwards to ensure full coverage.
For most masonry surfaces, one liberal coat is sufficient. However, highly porous substrates may require a second application, which should be applied as soon as the first coat is touch dry. When treating external timber, two coats are required for optimal performance.
As Cromar Exterior Water Seal forms a hydrophobic barrier, it must be used as a final protective treatment and should not be overpainted. The presence of the water-repellent coating may impair the adhesion of future decorative or protective coatings.
Coverage will vary depending on the porosity and surface texture of the material being treated. As a general guideline, one litre of product will cover approximately 2 to 4m² per coat. On highly porous surfaces, expect lower coverage rates and consider a second coat to ensure full saturation and water-repelling efficacy.
Drying times will be influenced by ambient temperature, humidity, and the type of surface being treated. Under normal conditions, surfaces treated with Cromar Exterior Water Seal will become touch dry within a few hours.
A second coat, if required, should be applied only after the first coat has sufficiently dried to avoid saturation run-off. Final curing will occur over the following 24 to 48 hours, depending on environmental conditions.
All tools, brushes, and spray equipment must be cleaned immediately after use with white spirit. Ensure any excess product is returned to the container with the lid tightly sealed to prevent evaporation and contamination. Do not dispose of cleaning residues or waste product into drains, watercourses or unapproved waste systems.
Store Cromar Exterior Water Seal in a tightly closed original container in a cool, dry place at temperatures between 8°C and 25°C. Avoid exposure to direct sunlight and protect from frost. If water or condensation enters the container, the product may gel and become unusable, so containers must be kept sealed when not in use.
The product has an indefinite shelf life if stored correctly. Cromar Exterior Water Seal contains volatile organic compounds (VOCs) with a content of approximately 690 g/l, in compliance with the EU limit for this category of 750 g/l (2010) under category 2(h).
A) Cromar Exterior Water Seal is a clear, solvent-based water repellent specifically designed to protect external porous surfaces from moisture ingress. It works by deeply penetrating the surface and forming an invisible barrier that actively repels water while still allowing the substrate to breathe. This makes it ideal for use on external brickwork, concrete, natural stone, paving slabs, asbestos cement, and preservative-treated timber. By preventing water from soaking into these materials, the product helps to reduce surface erosion, staining, moss and algae growth, frost damage, and other moisture-related deterioration, thereby extending the life and appearance of exterior surfaces.
A) Cromar Exterior Water Seal is compatible with most porous exterior surfaces, including traditional brickwork, natural stone, concrete paving, asbestos cement sheeting, and timber that has already been treated with a wood preservative. However, it is not suitable for surfaces that have been painted, sealed with non-breathable coatings, or are intended to be painted in the future, as the hydrophobic barrier it creates can interfere with adhesion. The product is designed exclusively for exterior applications and should never be used on internal surfaces, polished stone, or non-porous materials.
A) Cromar Exterior Water Seal functions by penetrating deeply into porous materials where it reacts to form a water-repellent layer within the substrate. This hydrophobic barrier prevents liquid water from being absorbed while still allowing water vapour to escape. This breathability is crucial for maintaining the integrity of masonry, stone and timber, as it reduces the risk of trapped moisture, which can cause blistering, cracking or biological growth over time. Its protective layer helps avoid issues like frost damage, salt staining, and efflorescence caused by recurring dampness.
A) While Cromar Exterior Water Seal offers long-lasting protection, it is not considered a permanent treatment. The durability of the protection will vary depending on exposure to environmental conditions such as UV radiation, rainfall, and frost, as well as the porosity of the substrate. On average, treated surfaces can remain protected for several years, but highly exposed or weathered areas may require reapplication every 4 to 5 years to maintain peak water repellence. Surfaces should be monitored periodically for signs of water absorption or moss growth to determine when re-treatment is necessary.
A) No, Cromar Exterior Water Seal is designed to be a final protective finish and should not be overpainted. The hydrophobic layer it forms actively repels water and any additional coatings applied on top—such as paints, stains, or renders—are unlikely to adhere properly. This makes it unsuitable for use on surfaces where a decorative finish is planned. If a decorative finish is required, the surface should be treated with compatible primers and coatings, and Cromar Exterior Water Seal should not be used in that instance.
A) While Cromar Exterior Water Seal is safe to use in proximity to windows and metal fixtures, care must be taken during application to avoid accidental overspray or splashes onto glass, metal, or painted joinery. The product may leave smears or stains on non-porous or sensitive surfaces, especially glass, if not wiped away immediately. Masking off these areas before application is highly recommended. If contact does occur, affected surfaces should be cleaned immediately using white spirit before the product dries.
A) Proper surface preparation is essential to ensure maximum effectiveness. All surfaces must be completely dry and free from dirt, dust, oil, grease, moss, lichen, algae, or loose particles. If the surface requires cleaning, it should be done using clean water only, without detergents or soaps that could leave residues. Washed surfaces must be allowed to dry thoroughly for two to three days before applying the seal. Any cracked mortar joints or damaged pointing should be repaired in advance to prevent water ingress behind the treated surface.
A) Cromar Exterior Water Seal can be applied using a soft-bristled brush or a low-pressure spray system fitted with a coarse nozzle. Spraying is generally faster and more consistent for larger areas, but brushing may be more suitable for detailed work or awkward surfaces. Application should always be performed from top to bottom on vertical surfaces to ensure an even and continuous coat. Avoid fine misting, as atomised spray may reduce the effectiveness and lead to unnecessary loss of material through drift. Shake the container well before and during use.
A) In most cases, a single liberal coat of Cromar Exterior Water Seal is sufficient for masonry and stone surfaces, provided the substrate is of average porosity. Highly absorbent materials such as soft brick or sandstone may benefit from a second application. This second coat should be applied while the first is still tacky or just touch dry—usually within a few hours—to ensure full penetration and avoid layering. When applying to external timber, two coats are recommended to achieve optimal water repellency and durability.
A) Under normal conditions, Cromar Exterior Water Seal will become touch dry within a few hours of application. However, drying times can vary depending on ambient temperature, humidity, and the porosity of the surface. Full curing of the product generally takes 24 to 48 hours. During this curing period, it is important to protect treated surfaces from rainfall, condensation, or foot traffic to allow the water-repellent barrier to fully develop. Once cured, the treatment becomes invisible and water repellent.
A) The coverage of Cromar Exterior Water Seal depends on the porosity and surface texture of the material being treated. As a general guide, 1 litre of product will cover approximately 2 to 4 square metres per coat. Rough, highly absorbent surfaces such as sandstone or aged brickwork may require more product and could fall toward the lower end of this range. For smooth or lightly porous materials, coverage will be higher. Always ensure full saturation of the surface to achieve effective protection.
A) Cromar Exterior Water Seal must only be applied to dry surfaces in dry weather conditions. The product will not bond effectively to damp or waterlogged materials, and applying it during wet or frosty conditions can lead to poor performance or surface whitening. Ideally, the product should be applied when temperatures are between 8°C and 25°C, with no rain forecast for at least 24 hours. Application should be avoided for two to three days following heavy rainfall to ensure surfaces are completely dry.
A) All tools and application equipment used with Cromar Exterior Water Seal must be cleaned immediately after use with white spirit. If the product is allowed to dry on brushes or spray tools, it may be difficult to remove. Dispose of any cleaning residues responsibly and do not pour them into drains or watercourses. Always seal the container tightly after use to prevent solvent evaporation and contamination of the remaining product.
A) Yes, Cromar Exterior Water Seal is suitable for both professional contractors and DIY users. It is supplied ready to use, with no dilution or mixing required, and can be applied with basic tools such as a brush or garden sprayer. Clear application guidelines and ease of use make it accessible to homeowners looking to protect brickwork, patios, garden walls or outbuildings. Users should always follow health and safety instructions, including wearing gloves and eye protection, and avoid using the product in enclosed or poorly ventilated spaces.
A) Cromar Exterior Water Seal offers several key benefits. It penetrates deeply into porous materials to provide long-lasting water repellence without altering the surface appearance. It helps prevent common moisture-related problems such as efflorescence, frost damage, biological growth, and surface staining. The product allows the surface to remain breathable, reducing condensation risk. It is easy to apply, fast drying, and requires minimal maintenance after application. Its solvent-based composition also provides more durable protection compared to many water-based alternatives.
A) Yes, Cromar Exterior Water Seal is suitable for use on both vertical and horizontal surfaces. It is commonly applied to brick façades, block walls, garden features, paving slabs, and patio stones. When using on horizontal surfaces, extra care should be taken to ensure thorough saturation, and the area should be protected from foot traffic during curing. Two coats may be beneficial for paving or walkways to provide a stronger barrier against water penetration and help prevent moss and algae build-up.
A) Cromar Exterior Water Seal is suitable for use on preservative-treated external timber such as fencing, gates, sheds, or timber cladding. It adds a layer of moisture repellence that complements the protection already offered by wood preservatives. Two coats are recommended for timber to ensure full coverage and durability. However, the product should not be used on untreated or freshly sawn timber that has not first been treated with an appropriate wood preservative.
A) Yes, by preventing water ingress and surface moisture retention, Cromar Exterior Water Seal helps reduce the conditions that support moss and algae growth. Surfaces treated with the product are less likely to retain dampness, making them less hospitable to biological growth. While the product is not a biocide and does not actively kill existing moss or algae, it serves as an excellent preventative measure. For areas with existing growth, surfaces should be cleaned beforehand using an appropriate moss or algae remover.
A) Cromar Exterior Water Seal is solvent-based and contains volatile organic compounds (VOCs), with a VOC content of approximately 690 g/l. This is within the EU regulatory limit of 750 g/l for its category, making it compliant for use across the UK and EU. While it is not classed as hazardous to the environment under normal use conditions, users should take care not to allow runoff or waste product to enter drains, watercourses, or soil. Empty containers and waste must be disposed of in accordance with local regulations.
A) Cromar Exterior Water Seal should be stored in its original, tightly sealed container in a cool, dry place, away from direct sunlight and sources of ignition. Storage temperatures should remain between 8°C and 25°C. The product must be protected from frost and moisture ingress. If water or condensation enters the container, the product may thicken or gel, making it unusable. When stored correctly, Cromar Exterior Water Seal has an indefinite shelf life, ensuring long-term usability for future applications.
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