How to calculate coating and render material quantities

Step-by-step procedure

1. 1

   Measure gross area

   Take each elevation length × height from drawings and verify on site. Keep elevations separate so ordering matches the batching plan.

2. 2

   Adjust for openings

   Deduct openings larger than 2 m² only, and add reveal areas (perimeter × depth) back in. Small windows are treated as solid wall.

3. 3

   Pick the practical coverage rate

   Data sheets quote theoretical coverage on a smooth substrate. Reduce it by 10–25% for rough render, high-suction block or heavy texture. For textured coatings use kg/m² per grain size, not litres.

4. 4

   Multiply by coats

   Count every layer in the system: primer, basecoat, texture, topcoat. Each has its own coverage rate — calculate them as separate line items, not one blended figure.

5. 5

   Add wastage and a control batch

   Add 5% for roller, 10% for trowel, 15–20% for spray, plus scaffold losses. Order one extra pail of the same batch per colour and store it for later touch-ups.

6. 6

   Reconcile on site

   Record actual consumption per elevation against the calculation. Consumption far below plan usually means the film is too thin — a warranty risk, not a saving.

Worked example

A 400 m² facade with a 1.5 mm textured coating at a practical rate of 2.5 kg/m²: 400 × 2.5 = 1,000 kg, plus 10% trowel wastage = 1,100 kg. Primer at 8 m²/L for one coat: 400 ÷ 8 = 50 L, plus 5% = 53 L.

Order in whole batches

Round up to full pails and, for coloured products, ask for a single production batch per elevation. Mixing batches mid-wall is a common cause of visible shade differences.