Render & Monocouche Coverage Calculator
Calculate the number of bags of render or monocouche needed for any wall area, accounting for coat thickness and surface texture.
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Rendering Guide
What should I know about Coverage Rates for Render?
Coverage rates per 25kg bag (approximate): traditional sand/cement scratch coat at 12mm: approximately 0.9-1.0 m² per 25kg bag. Top coat at 6mm: approximately 2.0-2.2 m² per 25kg bag. Monocouche at 15mm (e.g. K-Rend, Weber One): approximately 0.7-0.8 m² per 25kg bag. Thin coat (1.5mm silicone/acrylic): approximately 6-7 m² per 25kg bag. Roughcast at 18mm: approximately 0.6-0.7 m² per 25kg bag. These rates vary with surface texture and application method — always check the manufacturer's specific product data sheet rather than relying on general coverage rates, since formulations vary between brands.
What's the key thing to understand about Preparation is Critical?
The render will only be as good as the background. Essential preparation: brush off all loose material, dust, and organic growth. Allow new blockwork to cure for at least 28 days. PVA/SBR bonding agent: apply to very smooth or low-absorption surfaces (dense concrete, glazed bricks) to improve adhesion. Allow to become tacky before applying render (not wet). Expanded metal lath (EML) or beads: fix stop beads at all reveals and edges. Use angle beads at external corners. Ensure all electrical and plumbing fittings are fitted with proper mounting boxes and covers before rendering, since retrofitting them afterwards means cutting back into the finished surface.
What's the difference between Monocouche and Traditional Render?
Monocouche (single-coat): factory-coloured through-coloured system. Scratch, fill, and finish in one pass. Faster application. More expensive per bag but fewer bags overall. Better crack resistance (flexible polymer additives). Self-cleaning properties on silicone systems. Traditional 2-coat: scratch coat (1:4 cement:sharp sand at 12mm). Fibrous undercoat or topcoat. Finish coat with texture/colour wash applied separately. Lower material cost. More skill-intensive. Paint required for colour. Both approaches can achieve a good, durable finish when applied correctly — the choice usually comes down to budget, desired texture, and the contractor's own preference and experience.
What do I need to know about Mixing and Application?
Traditional sand/cement render mix: 1 part cement : 4 parts sharp sand (scratch coat). 1 part cement : 5-6 parts sharp sand (top coat). Use a plasticiser (not washing up liquid) in the mix for workability. Mix ratio for water: approximately 0.4-0.5 litres per kg of dry material. Mix to a stiff but workable consistency — render should stay on an inverted trowel. Application: pre-dampen the surface. Apply scratch coat, press firmly, rule off to beads/guides. Score horizontally before it fully sets, if a scratch-coat key is needed for a subsequent finish coat to bond to.