Monocouche Render Calculator — Bags, Cost & Beads

Monocouche (meaning 'one coat' in French) is a factory-mixed render applied in a single 15-25mm coat, compared to traditional sand and cement which requires 2-3 coats. Monocouche render comes pre-coloured in a wide range of colours, so no painting is needed. It is more expensive per m² than sand and cement but saves significant labour time. Popular UK brands include K Rend, Weber and Parex. For traditional sand and cement rendering, use our Rendering Calculator.

A genuine one-coat monocouche covers roughly 0.75–0.80 m² per 25kg bag at the standard 20mm application thickness, so you need about 1.25–1.35 bags per m² of wall. The exact rate is per-product: K Rend K Mono ~0.78 m²/bag (1.6 kg/m²/mm), Weber Pral M ~0.75 m²/bag (~25 kg/m² at 15mm), Parex Monorex GF ~0.80 m²/bag. Always add 10% wastage for cutting, corners and application losses. Note that K Rend Silicone TC15/TC30 are thin-coat topcoats (~5 m²/bag at ~3mm over a separate basecoat), not monocouche, so they cover far more per bag, so use K Mono for a one-coat monocouche job.

Reinforcing mesh (160g/m² alkali-resistant glass fibre) is recommended at all junctions between different substrates (e.g. block to concrete, or over EWI joints), around window and door openings, and in areas prone to cracking. Many specifiers now require mesh over the entire wall area for belt-and-braces protection. The mesh is embedded into the first pass of render. Allow 15% extra for overlaps (minimum 100mm overlap at joints).

Essential accessories include: bellcast/drip beads along the base of all rendered walls (to prevent water tracking underneath), corner beads on all external corners (for protection and a clean edge), and stop beads where the render terminates (around windows, doors, and at abutments). All beads should be stainless steel or PVC for longevity. A primer or stabiliser (e.g. K Rend R7 Acrylic Primer) is applied to high-suction or difficult substrates before rendering to control suction. (Note: K Rend HP12 is a polymer base coat, not a primer. Confirm the correct preparation product for your substrate against the manufacturer's system specification.)

Monocouche render should not be applied in temperatures below 5°C or above 30°C, or in direct strong sunlight. Initial set takes 4-8 hours, after which the surface can be scraped back to create a textured finish. Full curing takes approximately 28 days. The render should be protected from rain for the first 24-48 hours. Do not apply if frost is forecast within 24 hours. For painting over older render, see our Masonry Paint Calculator.

As a 2026 supply-and-fit guide, monocouche rendering typically costs around £55–£75 per m² for standard colours, rising to roughly £90 per m² for bespoke colours or complex detailing. Budget jobs in plain colours can start nearer £35–£45 per m². Of that, materials are usually only about £8–£14 per m² (a 25kg bag is around £13–£15 and covers roughly 0.75–0.8 m² at 20mm). Most of that cost is labour at about £35–£60 per m², plus £5–£10 per m² for beads and mesh and £3–£6 per m² for primer or basecoat. A two-person team renders roughly 15–25 m² per day. These are indicative trade-cost-guide ranges, not a fixed price, so always get itemised local quotes. Enter your bag price in the calculator above for a materials-only cost estimate.

Working from typical 2026 supply-and-fit rates of about £55–£75 per m², a small 2-bed bungalow (around 100 m² of wall) is commonly in the £4,000–£7,500 region, a 3-bed semi (around 120–150 m²) roughly £6,500–£11,000, and a larger 4-bed detached (200 m²+) from around £11,000 upwards. This depends on access, scaffolding, substrate condition, number of openings and colour choice. Premium or bespoke colours, heavy detailing and difficult access push costs toward the upper end. These are guide figures from UK trade cost surveys, so get at least three itemised quotes. Use the calculator above to estimate the number of render bags so you can sense-check the materials portion of a quote.

Yes, re-rendering an external wall can be controllable work under the Building Regulations. Approved Document L Volume 1 (2021 edition, incorporating 2023 amendments) defines ‘renovation of a thermal element’ to include providing a new render layer on the external surface of a wall (paragraph 11.2). If more than 50% of an individual wall’s surface is renovated, or the work is a ‘major renovation’ (more than 25% of the whole external building envelope), then under paragraph 11.3 the whole wall should be improved to meet the U-value in Table 4.3 column (b): 0.30 W/(m²·K) for a wall upgraded with internal or external insulation. This does not apply if that is not technically/functionally feasible or cannot achieve a 15-year payback. In practice this usually means adding external wall insulation behind the render. Patch repairs and re-rendering smaller areas generally fall below these triggers. Monocouche over an existing wall does not normally need planning permission as it is usually permitted development, but listed buildings and conservation areas are exceptions, so check with your local authority and confirm the latest requirements on gov.uk. To size the insulation, see our U-Value Calculator.

Monocouche is a single-coat render applied at a nominal 15–25mm, with 20mm the usual standard. The minimum finished thickness after scraping back is generally 15mm, and it is built up in two passes rather than one thin layer. For more exposed walls, manufacturers and the code of practice favour the thicker end of the range: roughly 16mm for sheltered to moderate exposure and around 20mm for severe exposure. Always follow the specific product data sheet, since maximum thickness per pass is limited. The relevant standards are BS EN 13914-1:2016 (Design, preparation and application of external rendering — code of practice) and BS EN 998-1:2016, under which monocouche is a type ‘OC’ one-coat render for external use, classified for capillary water absorption (classes W0/W1/W2); a more weather-resistant class should be specified for exposed elevations. The calculator’s thickness selector adjusts the bag count automatically, as a fixed bag volume covers more m² at 15mm than at 25mm.