K-Rend Render Calculator — Full Silicone System Materials

A complete K-Rend silicone render system consists of five layers: K Rend Primer TC applied to the substrate, a basecoat (typically K Rend HP12 Base Coat at a nominal 4-6mm), fibreglass reinforcing mesh embedded in the basecoat, a second thin basecoat layer over the mesh, and then the silicone topcoat finish. You also need corner beads and stop beads around all openings and external corners. For traditional sand and cement render, see our Rendering Calculator. For monocouche options, try our Monocouche Render Calculator.

Coverage depends on the finish type and grain size. Silicone Thin Coat and TC15 (1.5mm grain) use approximately 2.5 kg/m² — roughly 10 m² per 25kg bucket. TC30 (a coarser 3mm grain) uses about 5.0 kg/m², roughly 5 m² per 25kg bucket. A 2mm scraped finish (K Rend Mineral TC2) uses around 2-2.5 kg/m². A Dash Receiver is a thick 6-10mm receiving coat at 1.5 kg per mm per m² — roughly 12 kg/m² at 8mm. These are K Rend PDS-stated rates — always add 10% for wastage.

K-Rend can be applied over sound existing render, but the surface must be clean, stable, and free from loose material. You should carry out adhesion tests first. If the existing render is painted, you may need to mechanically key the surface. K Rend recommend priming with Primer TC (colour co-ordinated to the topcoat) before applying the silicone thin-coat finish.

Each window or door opening requires stop beads on three sides — the head (top) and two jambs (sides). The sill is typically left bead-free with a drip detail. Because beads are discrete lengths that cannot be shared between separate openings, this calculator allows roughly 2.0m per side (about 6m per opening), which rounds up to three 2.5m lengths per opening — a safe allowance for typical window and door sizes. Smaller windows may use fewer; offcuts can be reused where lengths permit.

Per the K Rend Silicone TC data sheet, a freshly applied render basecoat should be allowed a minimum of 14 days to cure before the silicone topcoat is applied. Primer TC is applied to the cured basecoat and allowed 24 hours drying time before the topcoat goes on. Drying may be prolonged by low temperatures or high humidity, and the substrate and air temperature must be at least 5°C. Never apply any coat if rain is forecast, and protect freshly applied render from rain while it dries.