Stonewool Insulation

External Wall Insulation System with Mineral Wool

Stonewool Insulation specifically for use with external wall insulation systems.


Wetherby Stonewool Insulation is a consistent density, high strength, rock Stonewool slab with a water-repellent additive specifically designed for use in external wall insulation systems. It is dimensioned to be easy to handle and fix to a substrate.

Stonewool fibres realign during manufacture to increase impact strength without dramatically reducing thermal performance – making an ideal product for use behind a render finish.

Stonewool is a consistent density slab. This ensures better long-term compressive strength, high impact resistance, better thermal performance and a thinner, lighter product compared to other high-strength insulation options.


EWI Slab is specifically for use with external wall insulation systems. The slabs can be either adhered and mechanically fixed or just mechanically fixed to the substrate then overlaid with a mesh and render system to the designers/system suppliers specification. The slabs offer a solid and robust supporting substrate for the render and no fire stops are required.


EWI Slab is made from non-combustible inorganic rock wool, defined as Stonewool in BS 3533: 1981 and is manufactured in accordance with BSI Quality Assurance Standard BS EN ISO 9001: 2000.
Thermal Performance

EWI Slab has a thermal conductivity of 0.038 W/mK.

Fire Performance

EWI Slab is classified as Euroclass A1 to BS EN ISO 13501-1.

EWI Slab can be used up to an operating temperature of 850°C. In the event of fire it will emit negligible quantities of smoke and fumes. The heat emission from the products is insignificant.


EWI Slab is non-hygroscopic and is treated to ensure its water repellency. It is odourless, rot proof, does not sustain vermin and will not encourage the growth of fungi, mould or bacteria.


EWI Slab is free from CFCs, HCFCs and any other material with ozone depletion potential in its manufacture and content and represents no known threat to the environment.

EWI Slab’s manufacture has a low impact on the environment and is classified as Zero ODP and Zero GWP.

Physical Qualities of Phenolic Insulation Moisture Resistance

EWI Slab contains a water repellent additive to ensure that no liquid water is able to pass through the slab and reach the existing masonry during installation and construction.

Handling and Storage

EWI Slab is easy to handle and install, being lightweight and easily cut to size.

EWI Slab is supplied in polythene packs, stacked on pallets for temporary protection during transit or on site. For longer term outside storage (stock or site) the pallets should be stored under a secure waterproof covering.

Product Data

Thickness (mm) Thermal conductivity (W/mK) Thermal resistance (m2K/W) Length  (mm) Width (mm)
150 0.038 3.90 1200 600
140 0.038 3.65 1200 600
120 0.038 3.15 1200 600
110 0.038 2.85 1200 600
100 0.038 2.60 1200 600
90 0.038 2.35 1200 600
80 0.038 2.10 1200 600
40 0.038 1.05 1200 600

All dimensions are nominal

bullet point  For NBS Plus Information, click here: NBS Plus



  • Offers solid support to render
  • Superior fire resistance properties
  • No fire stops required
  • Excellent thermal performance
  • Excellent acoustic insulation