Rendering — layer thickness, substrate and consumption

The geometric render quantity is simple: the area multiplied by the average layer thickness gives a volume. On an uneven substrate the layer thickness varies, so use a sensible average.

Example: 20 m² with 12 mm of render = 20 · 0.012 = 0.240 m³ ≈ 240 L of net layer volume. Add your own shrinkage/waste allowance for application and compaction.

• 01Absorbency: a highly absorbent substrate draws water out of the render and may require pre-wetting or priming.
• 02Adhesion: the substrate must be clean, sound and free of grease and loose particles.
• 03Layer build-up: some solutions are applied in several layers — each layer has its own thickness.

The volume is only a starting point. The actual consumption in kg or bags depends on the product's density and yield, which are given in the supplier's datasheet — typically stated as kg per m² per mm of layer thickness.

'Rendering' covers several surface techniques that differ in thickness, mortar and appearance. The choice follows the substrate and desired result — a smooth interior wall and a robust plinth are not the same work.

• 01Rough plaster — a load-bearing, levelling layer of mortar that corrects the substrate. Scraped off and felted or finished after.
• 02Fine render — a thin, fine-grained final coat on top of the rough render that gives the final smooth surface.
• 03Water scouring — a thin mortar layer scoured with a sponge/felt, so the stone structure is visible through. Common on brick as a tight, uniform façade.
• 04Repointing — a thin, covering coating brushed with a mortar brush; gives a light, uneven surface, widely used on older and heritage masonry.
• 05Floating — rough render/mortar is floated with a float board so the aggregate shows lightly in a matte rough surface.
• 06Sack finish — mortar is rubbed with a piece of sack/cloth, so the joints are filled and the stone is partially covered; a rustic, semi-opaque look.