Roof Waterproofing Coatings · an Amrize brandBleed-blocking base coat for asphalt and bituminous substrates — locks in the oils that would otherwise bleed through silicone and stain it brown.
The jobs this product is specified for, day in day out.
Locks in the oils in weathered bituminous felt before a silicone top coat.
The substrate most likely to bleed brown through a pale coating in summer heat.
Required on warranted work over SBS — the bleed risk is highest here.
What the data sheet actually gives you on site.
Asphalt oils migrate up through silicone in warm weather. The bleed trap locks them in so a white roof stays white.
Specified on warranted installations over SBS felt — skip it and the warranty position changes.
Around 9.3 m² per 3.78 L per coat at a continuous 6 mil (0.15 mm) dry film — a small cost against a re-coat.
Weathered bitumen over two years old may not need it. We will tell you when it does.
The facts that matter, straight from the product data.
| Type | Single-component bleed-trap primer / base coat |
| Applied at | Continuous 6 mil (0.15 mm) dry film |
| Coverage | Approx. 9.3 m² per 3.78 L per coat (Gaco PDS) |
| When required | New bituminous roofing or asphalt-rich felts that bleed oil under heat; weathered bitumen over 2 years old — test first |
Type your area and we’ll do the maths — derivation shown, nothing hidden.
Everything from the manufacturer’s literature — open the part you need.
Specialised Oil Encapsulation – Effectively locks in oils and prevents them from migrating to the surface, ensuring a clean and uniform finish for topcoats.
Enhanced Substrate Compatibility – Proven adhesion to MOD BIT, BUR, asphaltic membranes, galvanised steel, polyurethane foam, and concrete (adhesion testing advised on all single-ply membranes).
Performance-Driven Acrylic Film – Delivers excellent tensile strength, elongation, and tear resistance, creating a robust foundation for long-term waterproofing systems.
Low-VOC, Environmentally Compliant – Water-based formula with VOC content below 50 g/L for safer handling and compliance with environmental standards.
Warranty Compliance – Required under Gaco’s warranty programme for SBS substrates and recommended for other asphaltic surfaces to ensure full system eligibility.
User-Friendly Application – Easy to mix and apply using brush, roller, or spray, with excellent workability in a wide range of site conditions.
GacoFlex A4271 Bleed Trap™ Base Coat is ideal for protecting existing felt and asphalt roof covers from oil bleed through which can damage the appearance of the Gaco S42 Silicone Roof Coating:
Asphaltic Roof Preparation – Creates a stable, sealed surface ready for Gaco silicone or acrylic topcoats.
Warrantable Roof Systems – Essential underlayer for Gaco warrantable SBS-modified bitumen installations.
Surface Stabilisation – Reduces risk of coating discolouration or failure due to oil migration.
Compatibility Layer – Provides a bonding surface for coatings over challenging bituminous substrates.
Surface Preparation: Ensure surface is clean, completely dry, and free of loose granules, dust, grease, or biological growth. Do not pressure wash asphalt surfaces.
Mixing: Stir until homogeneous before use.
Application Temperature: 50°F to 110°F (10°C to 43°C).
Application Method: Roller, brush, or airless sprayer (2,000–3,000 psi, tip size 0.025–0.040 in).
Coverage Rate: 1 gallon per 100 sq. ft. (3.8 L per 9.3 m²) per coat. Maintain continuous 6 mil dry film thickness for effective bleed blocking.
Dry Time: Minimum 4 hours at 75°F (24°C) and 50% RH. Longer in cooler or more humid conditions.
Topcoating:
S4200 & GacoRoof (S1600): May be applied directly once A4271 is fully cured (adhesion test recommended).
Proper surface preparation is critical for achieving maximum adhesion, ensuring effective oil encapsulation, and securing the long-term performance of the GacoFlex A4271 BleedTrap™ Base Coat. Bituminous substrates, in particular, require thorough cleaning to ensure the coating bonds correctly and fully blocks oil migration.
1. Inspection
Assess the roof for cracks, blisters, loose material, or signs of water damage, and complete necessary repairs before coating.
Identify areas of heavy contamination such as grease, oil deposits, moss, or algae.
2. Cleaning with GacoWash
Clean all surfaces with GacoWash Concentrated Cleaner, diluted according to manufacturer’s instructions.
Apply with a low-pressure sprayer or brush, working the cleaner into the surface to loosen dirt, biological growth, and contaminants.
Allow the cleaner to dwell as directed, then thoroughly rinse off.
Do not pressure wash asphalt surfaces — use controlled rinsing to prevent moisture penetration into the substrate.
Areas with stubborn grease or contamination may require additional scrubbing or repeat cleaning.
3. Drying
Ensure the substrate is completely dry before applying A4271 BleedTrap™.
Avoid application after recent rainfall or during conditions of persistent high humidity.
4. Masking & Protection
Mask off areas not intended for coating, including roof edges, skylights, flashings, and adjacent walls.
Protect sensitive building materials, vehicles, and landscaping from overspray.
5. Adhesion Testing
Perform an adhesion test on all single-ply membranes and unfamiliar substrates.
Only proceed with full application once satisfactory adhesion results are confirmed.
The GacoFlex A4271 BleedTrap™ Base Coat is specifically formulated to work in direct combination with GacoFlex S42 High-Adhesion 100% Silicone Roof Coating. When applied over asphaltic substrates, A4271 encapsulates migrating oils, creating a clean, stable base that ensures S42 bonds seamlessly without the need for any additional primer.
Once A4271 has fully cured — typically a minimum of 4 hours at 75°F (24°C) and 50% RH — S42 can be applied directly. In cooler or humid conditions, allow extra curing time to ensure the base coat is completely dry before top coating.
This system is designed for maximum compatibility, delivering a uniform, bleed-free surface that enhances the appearance, durability, and long-term performance of the finished roof.
Safe handling of GacoFlex A4271 BleedTrap™ Base Coat is essential to protect applicators, building occupants, and the environment. Always read and follow the full Safety Data Sheet (SDS) before use.
1. Personal Protective Equipment (PPE)
Eye Protection: Wear safety glasses or chemical splash goggles.
Skin Protection: Use chemical-resistant gloves and protective clothing to avoid skin contact.
Respiratory Protection: When spraying or working in confined areas, use a properly fitted respirator suitable for water-based acrylic coatings.
Footwear: Wear safety footwear with slip-resistant soles when working on roof surfaces.
2. Work Area Safety
Ensure adequate ventilation during application and curing, particularly in enclosed or partially enclosed spaces.
Prevent access to the work area by untrained personnel during application.
Avoid working on wet, slippery, or unstable surfaces.
3. Safe Handling
Do not eat, drink, or smoke when handling the product.
Avoid breathing spray mist.
Wash hands, forearms, and any exposed skin thoroughly after handling.
4. Environmental Protection
Do not discharge product into drains, watercourses, or onto the ground.
Collect and dispose of waste material, empty containers, and wash water in accordance with local environmental regulations.
5. First Aid Measures
Eye Contact: Rinse cautiously with clean water for several minutes. Remove contact lenses if present and easy to do. Continue rinsing and seek medical advice if irritation persists.
Skin Contact: Wash with soap and water. Seek medical attention if irritation develops.
Inhalation: Move to fresh air and keep comfortable for breathing. Seek medical advice if symptoms persist.
Ingestion: Rinse mouth and do not induce vomiting. Seek medical attention immediately.
6. Fire Safety
Product has a flash point above 200°F (93°C) and is water-based; it is not classified as flammable.
In the event of a fire, use water spray, foam, dry chemical, or CO₂ to extinguish.
Available in: 19 litre pails
Shelf Life: 24 months in original, unopened containers when stored above freezing
Storage Conditions: Protect from freezing and excessive heat. Store in a dry, covered location.
Mixing: Stir thoroughly before each use to ensure a uniform product. Some separation may occur during extended storage — remix until homogenous.
These products are designed to work together — buying the full system is what qualifies the warranty.
Written by our technical team — free to download, no email required.
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