Waterproofing horizontal surfaces often forces a choice: build for robust concealment or for long-term exposure. Silcor 575 LB removes that dilemma. It delivers certified, high-performance waterproofing for both concealed horizontal areas and, when paired with Silcor Top Coat 75, provides a UV-stable and light foot trafficable finish. This single product simplifies specification and on-site logistics for critical horizontal applications.

Why this product exists

Silcor 575 LB is a one-part, high solids, polyurethane membrane developed for straightforward, cold application on horizontal substrates with falls. It cures via ambient humidity, forming a tough, flexible, and seamless elastomeric membrane. The formulation allows it to semi self-level, creating a smooth finish that is crucial for robust waterproofing in both non-exposed and, when overcoated with Silcor Top Coat 75, exposed horizontal areas.

The numbers that matter

• High Physical Properties: >5 MPa Tensile Strength and >800% Elongation. This exceeds Class III high extensibility requirements, providing a substantial safety margin for non-structural crack bridging and accommodating typical building movements without compromising the waterproof barrier. These numbers prevent callbacks from membrane failure due to substrate movement.
• Semi Self-Levelling: Its formulation allows for flow on horizontal substrates, resulting in a smooth, continuous film. This ensures full contact with the substrate, eliminating voids that could trap water or become stress points, critical for long-term performance on flat or gently sloped areas.
• Low VOC: <110g/L. This signifies a reduced environmental impact and improved site air quality. It minimises health and safety concerns for applicators and other trades, supporting safer working conditions on enclosed or semi-enclosed sites.
• Class III Certified: AS 4654.1 and AS/NZS 4858. This certification confirms the product meets Australian Standards for both external non-exposed and internal wet area waterproofing. It provides the necessary compliance for specifying critical horizontal areas like balconies, podiums, and wet area floors.

What it's like to use

Silcor 575 LB is applied cold with a roller or brush in two cross-directional coats. Substrates must be primed first with a compatible GCP primer, such as Silcor Primer BS for dry conditions or Epocote F100W for damp or green concrete. The membrane becomes tack-free in around four hours at 23°C/60% RH, with recoat possible after 12 hours. Full through-cure takes 48 hours, at which point it is ready for flood testing or topping. Clean application equipment immediately with xylene solvent.

Where this product excels

• Horizontal Roof Decks and Podium Slabs: Providing a seamless, fully bonded waterproof layer under screeds, pavers on pods, or landscaped areas. Its high elongation and tensile strength accommodate structural movement and bridge non-structural cracks.
• Balconies with Exposed Finishes: When overcoated with Silcor Top Coat 75, it offers a UV-stable, light foot trafficable finish. This ensures aesthetics and waterproofing integrity are maintained in exposed outdoor environments.
• Internal Wet Area Floors: Suitable for application either under or over screeds, providing robust waterproofing for bathrooms, laundries, and plant rooms. Its seamless application eliminates vulnerable joins.
• Green Roofs and Landscaped Decks: The membrane forms a durable barrier against water ingress. When protected with Protectoboard or Rapid-Drain, it withstands the pressures of soil loading and planting media, ensuring long-term performance in demanding environments.

How it fits in a real system

Silcor 575 LB is typically applied after detailing and priming, forming the primary waterproofing layer on horizontal surfaces. It requires a compatible GCP primer like Silcor Primer BS or Epocote F100W, selected based on substrate moisture conditions. For critical detailing, Silcor LM PU Sealant is used to form bond breaker fillets in internal corners and around penetrations, ensuring flexibility at stress points. Once cured, the membrane's protection strategy depends on the final finish: it can be covered by screeds with a tie coat (using an additional layer of Silcor 575 LB and blinded with aggregate), protected by Protectoboard or Rapid-Drain for backfilled or unbonded screed applications, or exposed to UV and light foot traffic when overcoated with Silcor Top Coat 75.

Choose this when

• When you need a single membrane for both concealed and exposed horizontal waterproofing. Silcor 575 LB provides the flexibility to perform in both scenarios with the appropriate top coat.
• When dealing with balconies, roof decks, podiums, or internal wet area floors. Its semi self-levelling properties ensure a smooth, continuous finish on horizontal substrates.
• When high movement capability is critical. Its >800% elongation bridges non-structural cracks and accommodates typical structural movements.
• When compliance with Australian waterproofing standards for Class III membranes is required. Silcor 575 LB is certified to AS 4654.1 and AS/NZS 4858.

Don't use this when

• Not for: heavy duty foot or vehicle traffic. Even with Silcor Top Coat 75, this membrane system is not designed for high-impact or vehicular loads. For trafficable applications, consider Silcor 580.
• Not for: vertical or ramped surfaces. Its semi self-levelling properties will cause it to run, making it unsuitable for non-horizontal applications.
• Not for: applications without an appropriate GCP primer. All Silcor membranes require a compatible primer for proper adhesion and system integrity.
• Not for: economical, non-exposed waterproofing where an exposed option is not required. For a lower-cost alternative focused solely on concealed applications, consider Silcor 560 HB Charcoal.

Silcor 575 LB vs. Silcor 560 HB Low VOC: Choosing the right horizontal membrane

While both Silcor 575 LB and Silcor 560 HB Low VOC are one-part, cold-applied polyurethane membranes from GCP, they are designed for different primary applications. Silcor 575 LB is specifically formulated for horizontal substrates, offering semi self-levelling properties that result in a smooth finish. This makes it ideal for areas like balconies and podiums where a high-quality aesthetic is desired, and crucially, it can be exposed to UV and light foot traffic when overcoated with Silcor Top Coat 75. In contrast, Silcor 560 HB Low VOC is a thixotropic (non-sag) membrane. This characteristic makes it more suited for vertical applications and detailing, but it must always be concealed as it is not UV stable. Choose Silcor 575 LB when your project requires a seamless, self-levelling horizontal membrane that offers the option of an exposed finish; opt for Silcor 560 HB Low VOC when a non-sag, concealed membrane is needed for vertical or detailed work.