Roof Waterproofing Coatings · an Amrize brandWater-based acrylic elastomeric roof coating — the lower-cost option for pitched commercial and industrial metal roofs that don't pond.
The jobs this product is specified for, day in day out.
Free-draining profiled metal where budget matters more than ponding resistance.
Large areas needing a reflective, cost-effective refurbishment.
Refreshing an ageing but intact acrylic system.
What the data sheet actually gives you on site.
A 15-year system at a materially lower price than silicone, where the roof drains properly.
When applied to specification as a two-coat system.
Cuts roof surface temperature on big south-facing spans.
If water stands on the roof, this is the wrong product — that is S42 territory, and we will say so.
The facts that matter, straight from the product data.
| Type | Water-based acrylic elastomeric coating |
| Warranty | 15 years when applied to specification |
| Use | Pitched commercial / industrial metal roofs without ponding |
| Finish | White (other colours by special order), two-coat system |
| Not suitable for | Substrates that pond water — use Gaco S42 silicone there |
Type your area and we’ll do the maths — derivation shown, nothing hidden.
Everything from the manufacturer’s literature — open the part you need.
Airless Spray Equipment – Recommended for fast, uniform coverage of the acrylic waterproof coating. Use a high-pressure airless sprayer capable of delivering sufficient volume and pressure for thick, elastomeric materials.
Quality Rollers (1″–1.25″ nap) – Suitable for smaller areas, detailing, and edges. Ideal when spray application isn’t possible or access is restricted.
Soft-Bristle Brushes – Used for precision work around penetrations, flashings, seams, terminations, and other intricate roof details.
Mixing Equipment – A slow-speed mechanical mixer is required to ensure the coating is thoroughly blended before application without introducing air bubbles.
Protective Spray Shields & Masking Materials – Helps prevent overspray on windows, walls, HVAC units, vehicles, or adjacent structures.
Wet Film Thickness Gauges – Essential for verifying correct application thickness to guarantee the acrylic waterproof coating performs as specified.
Cleaning Tools – As the product is water-based, standard cleaning materials (water, mild detergent, buckets, rags) support quick cleanup of tools and equipment.
Proper surface preparation is essential to ensure maximum adhesion and long-term performance of the acrylic waterproof coating. All roof surfaces must be clean, dry, structurally sound, and free from contaminants that could interfere with bonding. Remove dirt, grease, oil, biological growth, chalk, loose coatings, and weathered materials using approved cleaning methods such as pressure washing or mechanical abrasion. Any areas affected by algae, moss, or mildew must be treated with a suitable biocidal wash and thoroughly rinsed.
Inspect the roof substrate for damage, cracks, rust, blisters, or moisture entrapment. Repair defects using compatible patching materials, mastics, or primers recommended for the specific roof type. Metal surfaces must be free from active corrosion; treat rust as required before coating. Ensure all seams, penetrations, and terminations are properly sealed and reinforced. Allow surfaces to fully dry—standing water or damp substrates will compromise adhesion.
Primers may be required on certain substrates to optimise bonding; refer to the GacoFlex Roof Coating Guide for substrate-specific recommendations. Mask adjacent surfaces and protect sensitive areas from overspray. Only proceed with application when the weather conditions meet the required temperature and humidity ranges for an acrylic waterproof coating to cure correctly.
Primers
The choice of primer depends on the condition and type of substrate. While many surfaces allow direct application of the acrylic waterproof coating, certain roof systems require a primer to ensure optimum adhesion and long-term durability.
Metal Roofs: Use a corrosion-inhibiting metal primer where rust or oxidation is present to stabilise the surface and promote strong adhesion.
Modified Bitumen, BUR, and Asphaltic Roofs: Apply an asphalt-bleed blocking primer to prevent staining or discolouration migrating into the acrylic coating.
Concrete & Masonry: Highly porous or dusty substrates may require a penetrating primer to bind the surface and achieve uniform absorption.
Spray Polyurethane Foam (SPF): Generally compatible without primer, but weathered foam must be cleaned and re-primed if degraded or oxidised.
Always follow Gaco’s substrate-specific recommendations to ensure the primer matches the roof type and conditions.
Topcoats
For best performance, GacoFlex 127 Series should be applied in multiple coats to achieve the required dry film thickness. The second (topcoat) layer reinforces the waterproof membrane, increases UV resistance, and improves long-term durability.
UL 790 / ASTM E108 Fire Rating:
The GacoFlex 127 Series acrylic waterproof coating meets Class A fire performance requirements when installed as part of approved roofing assemblies. This ensures compliance with industry-recognised fire safety standards for commercial and residential buildings.
FM Approved Roofing Assemblies:
Selected GacoFlex systems incorporating the 127 Series are approved by FM Global, demonstrating tested performance for wind uplift resistance, weatherability, and long-term roof protection.
Energy Efficiency & Reflectivity Standards:
The white formulation delivers high solar reflectance and thermal emittance, supporting compliance with energy-efficiency guidelines and contributing to reduced heat absorption on low-slope roofing systems.
VOC-Compliant & Environmentally Responsible:
As a water-based acrylic waterproof coating, GacoFlex 127 meets low-VOC requirements for use in occupied buildings and environmentally sensitive projects, aligning with modern sustainability practices.
Manufacturer Testing & Quality Assurance:
GacoFlex 127 is produced under stringent quality-control procedures, with performance validated through tensile strength, elongation, adhesion, and weathering tests to ensure reliable, long-term service life.
Personal Protective Equipment (PPE):
Applicators should wear suitable PPE including gloves, safety glasses, long sleeves, and, where spraying, a respirator rated for fine particulates. Skin and eye protection is essential when handling any acrylic waterproof coating.
Ventilation Requirements:
Although water-based and low odour, the product should be applied in well-ventilated areas. Avoid use in confined spaces without mechanical ventilation to prevent buildup of vapour and ensure safe working conditions.
Avoid Inhalation & Contact:
Prevent inhalation of spray mist and avoid prolonged skin contact. If contact occurs, wash thoroughly with soap and water. Seek medical attention if irritation persists.
Safe Handling & Storage:
Store the coating in its original sealed container between recommended temperatures. Protect from freezing and direct sunlight. Keep all materials away from open flames, sparks, and incompatible chemicals.
Spill & Cleanup Procedures:
Clean spills immediately using absorbent materials. As a water-based acrylic waterproof coating, cleanup is straightforward with soap and water before drying occurs. Prevent product from entering drains or waterways.
Environmental Considerations:
Dispose of empty containers and waste materials in accordance with local regulations. Do not pour unused material into drains or the environment.
Application Safety:
Ensure roofs are structurally safe and access equipment is properly secured. Use fall-arrest systems where required. Avoid application in wet or icy conditions to reduce slip hazards.
Weather Conditions Matter:
Apply the acrylic waterproof coating only when temperatures and humidity fall within the recommended range. Low temperatures, high humidity, or approaching rainfall can delay curing and affect adhesion.
Do Not Apply to Damp or Wet Surfaces:
Moisture trapped beneath the coating can cause blistering, poor adhesion, or premature failure. Ensure all substrates are completely dry before starting work.
Film Thickness Is Critical:
Achieving the correct wet and dry film thickness is essential for long-term waterproofing performance. Use a wet film gauge during application to verify coverage.
Stir, Don’t Shake:
Mix the product thoroughly with a slow-speed mechanical mixer. Shaking can introduce air, causing bubbles and an uneven finish.
Primers May Be Required:
Some substrates—such as aged asphalt, rusty metal, or highly porous surfaces—require specific primers to guarantee proper adhesion and long-term durability.
Avoid Application During High Winds:
Overspray from airless equipment can travel significant distances. Use spray shields and masking to protect nearby vehicles, buildings, and sensitive surfaces.
Foot Traffic Limitations:
Once cured, the coating tolerates light maintenance foot traffic but is not intended as a walkable surface. Install walk pads where regular access is required.
System Integration:
For best results, use only Gaco-approved primers, reinforcement tapes, mastics, and topcoats to create a compatible, warrantable roofing system.
Follow Manufacturer Guidelines:
Always refer to the official GacoFlex application instructions for substrate-specific guidance, cure times, and system requirements.
Tell us about the building and we’ll spec the job free — the right system, the right quantities, and trade rates if you’re buying for a contract.
Tell us about your building and we’ll recommend the right system — foam, waterproofing or both — surveyed, specified and quoted at no cost.
