Rocksilk® EWI Slab - Rock Mineral Wool - 90mm

Brand: Knauf
£27.59 Incl. VAT
£27.59 Incl. VAT (regular price)
Please note: This product has a slightly longer lead time. Our team wiil notify you with an estimated delivery date.

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    Rocksilk® EWI Slab is a high-performance rock mineral wool insulation solution designed specifically for external wall insulation (EWI) systems. Holding a BBA Agrément Certificate (24/7271), this slab is ideal for application to the exterior of masonry or concrete walls in both new build and retrofit projects. The slabs can be either adhered and mechanically fixed or solely mechanically fixed, offering flexibility in installation.

    With a Euroclass A1 reaction to fire rating, Rocksilk® EWI Slab is fully non-combustible, removing the need for fire barriers and ensuring peace of mind for specifiers and installers. Manufactured with a water-repellent additive, the slabs help prevent moisture ingress, while their mineral wool composition delivers excellent thermal and acoustic performance. Rocksilk® EWI Slab is compatible with both silicone and mineral render systems, providing versatile design options.

    Key Benefits:

    • BBA-certified (24/7271) for EWI use on external masonry/concrete walls in residential and commercial buildings

    • No fire breaks required thanks to Euroclass A1 fire rating

    • Also available in a denser, stronger version – Rocksilk® EWI Slab Plus

    • Compatible with silicone and mineral renders for flexible finish options

    • Water-repellent additive for superior moisture resistance

    • Excellent sound absorption and reduction properties

    Technical Data

    Product Code 264382
    Board Size 90mm x 600mm x 1200mm (0.72m²)
    Material Rock Mineral Wool
    Certification BBA Agrément Certificate 24/7271
    Material Extruded Polystyrene (XPS)
    Thermal Conductivity (λ) 0.036 W/mK
    Thermal Resistance (λ) 1.65 m2K/W
    Tensile Strength 10 kPa
    Compressive Strength 30 kPa
    Reaction to Fire (Euroclass) Euroclass A1 (non-combustible)
    Water Absorption (long-term) WL(P) < 3 kg/m² (per BS EN 12087)
    Water Vapour Resistance Vapour resistivity 5.00 MN·s/g·m (negligible resistance)
    Density ≈ 100 kg/m³
    Application External Wall Insulation – masonry or concrete substrates

    Frequently asked questions

    Rocksilk® EWI Slab is suitable for use on external masonry or concrete walls in both new build and refurbishment projects. It can be adhered and mechanically fixed or solely mechanically fixed, depending on the system.

    No. Thanks to its Euroclass A1 reaction to fire rating, Rocksilk® EWI Slab is non-combustible and removes the need for fire barriers within the insulation system.

    Yes, Rocksilk® EWI Slab is compatible with both silicone and mineral render systems, providing flexibility in the external finish and aesthetic.

    The Plus version is denser and has a higher compressive strength (50 kPa vs 30 kPa), making it ideal for areas requiring enhanced durability or mechanical performance.

    Yes. Rocksilk® EWI Slab is manufactured with a water-repellent additive to resist moisture ingress and has low water vapour resistance, allowing the wall to breathe effectively.

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