Retrobase High Polymer Insulation Basecoat 25kg

Retrobase Basecoat is a polymer-modified composite mortar formulated for reinforcing and levelling with embedded mesh. It is vapour permeable and weather resistant, with an open time of 50–60 minutes at 20°C. Typical fresh mortar density is 1757g/l and water retention is 98%. The product achieves flexural strength >3.9N/mm2 and compressive strength >7.3N/mm2. Service temperature range is -20°C to +80°C.

Intended applications

The material is applied directly to insulation as part of SPS Envirowall External Wall Insulation systems and can also be applied to prepared masonry and blockwork as part of a render-only build-up. It is suitable for hand and spray application. Substrates explicitly listed include brick or block work and insulation types: mineral wool, phenolic, EPS and ICF.

Preparation

All substrates must be sound, clean, dry and free from anything that may impair adhesion. Do not apply to shiny surfaces. Scaffolding should be independently tied to permit uninterrupted application. Defects that could allow moisture penetration must be rectified. Mask adjacent areas and remove masking tape before the basecoat dries. Application should not proceed if substrate and ambient temperatures are below +5°C. Protect façades from rain, direct sun and wind; sheeting of the scaffold or façade is advised. Rendering should be avoided below DPC or within 150mm of ground level.

Mixing

Mix approximately 4.5 litres of clean water per 25kg bag using a suitable drill and whisk. Mix for 5 minutes, allow to stand for 2 minutes, then remix. Use as little water as necessary to achieve a workable consistency. The product may stiffen on standing; remix to restore workability. Do not add extra water. The product is also suitable for spray application.

Application — Adhesive bedding (where specified)

As an adhesive coat, work a thin, pressed trowelled coat across the full insulation board surface. Then comb Retrobase across the board with a 10x12mm notched trowel. Alternatively, apply in dabs ensuring even distribution and at least 60% coverage of the board surface. Dabs should not exceed 25mm thickness once the board is pressed to the substrate. Application temperature range is 5°C to 25°C.

Application — Reinforcing basecoat

Apply Retrobase to the prepared substrate with a stainless steel trowel, then comb with a 10x6 tooth trowel to achieve a consistent basecoat depth. Float the specified reinforcing mesh into the top of the wet basecoat, maintaining minimum 100mm horizontal and vertical overlaps. Reinforce corners at openings with 250x250mm mesh patches embedded diagonally into the wet basecoat. Allow the basecoat to set completely for at least 2–3 days before applying Envirowall acrylic or silicone finishes.

Coverage (guidance)

Approximate material usage (excluding wastage and dependent on substrate regularity) is:

• Adhesive coat: approx. 5–10kg/m2.

• Basecoat with armouring mesh on EWI systems: approx. 5–11kg/m2.

• Render-only to render carrier board with reinforcing mesh: approx. 5–11kg/m2.

• Render-only to brick/block work with reinforcing mesh: approx. 6–12kg/m2.
  Allowance should be made for uneven or misaligned substrates when ordering.
  
  

Limitations and weather

Do not apply if frost is forecast within 24 hours, in damp/wet conditions, in temperatures below 5°C or above 30°C, on elevations in direct sunlight, or to hot substrates. Surrounding elements (e.g., windows and sills) must be protected during application and early curing.

Compliance and reference standards

Specification clauses are available in NBS Section M20 Rendering. BS 5265 (Code of Practice for External Rendering) and BS 8000-10 should be followed. SPS Envirowall products are factory blended, tested and packaged under quality control procedures in accordance with BS EN ISO 9001 series.

Handling, packaging and storage

Supplied in 25kg paper sacks, typically palletised in quantities of 40 and shrink wrapped. Store in dry conditions above 5°C. Shelf life is 12 months from manufacture when stored correctly. Do not mix with other binders or additives. Dispose of material in accordance with local requirements; do not empty into the ground, watercourses or drains. Empty containers (including lids and wire handles) are recyclable.

Health & safety

Refer to the product health and safety data sheet for detailed guidance on safe handling and disposal.

Technical Data