Monocouche Render Calculator — Bags, Cost & Beads

This calculator estimates all materials needed for a monocouche render system including render bags, reinforcing mesh, beads and primer. It supports three genuine one-coat monocouche renders (K Rend K Mono, Weber Pral M and Parex Monorex GF), whose datasheet coverage rates are close but not identical, so the calculator uses a separate rate for each.

Note: K Rend Silicone TC15/TC30 are notmonocouche renders. They are thin-coat textured topcoats (~5 m² per 25kg bag at roughly 3mm grain) applied over a separate basecoat and primer, so they are not included here. K Mono is K Rend’s genuine one-coat monocouche.

How it calculates

Net wall area= Gross wall area − (Windows × 1.2 m²) − (Doors × 1.8 m²)

Render bags= Net area ÷ Coverage rate × Wastage factor. A 25kg bag yields a fixed mortar volume, so coverage scales inversely with thickness. Thinner application (15mm) increases m² per bag proportionally.

Coverage rates at 20mm (per 25kg bag)

• K Rend K Mono: ~0.78 m² per bag (1.6 kg/m²/mm, k-rend.co.uk)
• Weber Pral M: ~0.75 m² per bag (~25 kg/m² at 15mm, Weber UK)
• Parex Monorex GF: ~0.80 m² per bag (1.0–1.1 m²/bag at 15mm, Sika PDS)

Accessories

• Mesh: 160g/m² alkali-resistant, factor of 1.15 for 100mm overlaps
• Bellcast beads: Along the base of all rendered walls (2.5m lengths)
• Corner beads: On all external corners, full building height (2.5m lengths)
• Stop beads: Around windows, doors and render terminations (2.5m lengths)
• Primer: ~5.5 m²/litre, applied to substrate before rendering

Estimating cost

Enter a price per 25kg bag to get a materials-only cost for the render. As a 2026 UK guide, bags are typically around £13–£15 each and a full supply-and-fitmonocouche job runs roughly £55–£75 per m² for standard colours (up to ~£90 per m² for bespoke colours or complex detailing). Of that, materials are usually only £8–£14 per m² and labour the larger share. These are indicative trade-cost-guide ranges, so always obtain itemised local quotes.

Thickness & standards

Monocouche conforms to BS EN 998-1:2016as a type ‘OC’ one-coat render for external use, applied to BS EN 13914-1:2016(external rendering code of practice). The nominal thickness is 15–25mm (20mm standard; minimum 15mm finished, built up in two passes). Re-rendering an existing wall is ‘renovation of a thermal element’ under Approved Document L Volume 1 (2021, incorporating 2023 amendments): if more than 50% of a wall (or more than 25% of the whole external envelope, a major renovation) is renovated, the wall should be upgraded toward the Table 4.3(b) limit of 0.30 W/(m²·K) where feasible, usually via external wall insulation behind the render.