EWI-748 Lime Basecoat NHL 5 is a high-performance, lime-based bonding mortar designed to act as both an adhesive and reinforced basecoat within breathable external wall insulation systems, including mineral wool and wood fibre boards. The basecoat must be reinforced with alkali-resistant fibreglass mesh to provide structural strength, impact resistance and crack control within the system.

Formulated using natural hydraulic lime (NHL 5), fine natural pozzolans and carefully selected additives, it offers excellent adhesion, extended workability and long-term durability.

Its micro-porous structure allows moisture to pass through the wall and evaporate naturally, helping buildings regulate moisture effectively. Compared to cement-based alternatives, EWI-748 supports lower wall conductivity, improved thermal performance and a healthier internal environment.

Intended Uses

EWI-748 Lime Basecoat is suitable for internal and external applications across new build and renovation projects, including:

• Adhesion and reinforcement mortar for mineral wool and wood fibre insulation boards within breathable EWI systems
• Reinforced base layer over insulation prior to decorative lime finishes
• Basecoat requiring reinforcement with alkali-resistant fibreglass mesh

It is designed specifically for breathable insulation systems and should not be used as a basecoat beneath EWI-747 render. Once cured, EWI-748 should be protected with breathable finishes such as lime wash or lime paint or may be finished internally with EWI-749 Fine Finish Lime Plaster where specified.

Key Benefits

• Natural hydraulic lime binder (NHL 5) for strength and durability
• Designed specifically for mineral wool and wood fibre insulation systems
• Highly breathable, supporting natural moisture movement
• Excellent adhesion to insulation boards
• Extended working time for improved on-site usability
• Resistant to acid rain and salts
• Micro-porous structure promotes rapid vapour evaporation
• Helps reduce thermal conductivity compared to cement-based mortars
• Reinforced with alkali-resistant fibreglass mesh
• Eco-conscious formulation that absorbs CO₂ during carbonation

Compatible Products

EWI-748 Lime Basecoat is designed for use within breathable insulation systems only.

Wood Fibre & Mineral Wool Insulation

EWI-748 acts as both the adhesive and reinforced basecoat for wood fibre and mineral wool insulation boards, creating a fully breathable EWI build-up when reinforced with fibreglass mesh.

EWI-707 Lime Wash

Provides breathable protection once EWI-748 has cured, helping regulate carbonation while maintaining vapour permeability.

EWI-705 Lime Paint

Can be applied once fully cured to provide a decorative and protective breathable finish.

EWI-749 Fine Finish Lime Plaster

For internal applications requiring a refined finish, EWI-749 may be applied over cured and properly prepared EWI-748.

Substrate Preparation

Substrates must be firm, clean and sound, free from dust, grease, oils, salts, efflorescence, biological growth or loose material that could impair adhesion.

Where required, substrates should first be flattened and regularised using EWI-747 Lime Render NHL 3.5 before insulation boards are installed.

All backgrounds should be pre-dampened with clean water, ensuring they are moist but not saturated. This helps prevent rapid dehydration and promotes correct curing.

Product Preparation

Mix EWI-748 with clean water only, at a ratio of 4.5-5 litres per 21 kg bag.

• Pour water into a clean container
• Gradually add the powder while mixing
• Mix for 3-5 minutes until a smooth, lump-free consistency is achieved

Do not add excess water, as this may reduce mechanical strength.

Application

Adhesion of Insulation Boards

• Ensure the substrate is flat and regularised
• Apply EWI-748 to the back of the insulation board
• Use a 10 × 10 mm notched trowel to create a full-surface keyed adhesive layer
• Press the board firmly into position

Full-surface coverage is required to ensure stability and vapour continuity.

Reinforcement

• Allow boards to set before reinforcing
• Apply a 6–8 mm layer of EWI-748
• Embed alkali-resistant fibreglass mesh into the fresh mortar
• Cover and regularise without flattening the mesh

The reinforcement mesh must be 100% fibreglass, alkali-resistant, with a minimum mesh size of 5 × 4 mm and a weight of 160 g/m².

Typical basecoat thickness: 6–8 mm
Maximum thickness per coat: 8 mm

Learn how to install EWI-748 Lime Basecoat NHL 5

Technical Data

 Storage Conditions

Store in original, unopened packaging in a cool, dry location, protected from moisture and frost. Avoid water ingress. Shelf life is up to 12 months from the date of manufacture when stored correctly.