Two-coat sand cement render systems

Traditional two-coat sand/cement render uses site-batched OPC (ordinary Portland cement) and clean washed plasticising sand mixed at the required ratio (typically 1:4 OPC to sand for scratch coat, 1:5 for float coat) with a small amount of hydrated lime for workability. Boral OPC and Brickies (plasticising) sand are the most widely used materials for site-batched render in the eastern Australian market. In Australian Class 2 strata facade remediation, site-batched sand/cement render is specified where cost is the primary driver and the substrate is suitable for traditional render (rough textured concrete or masonry with adequate absorption). The two-coat system — scratch coat (12–15mm) combed to provide key, then float coat (6–10mm) — provides a structurally adequate render that meets AS 3700 requirements. However, site-batched renders are susceptible to mix ratio variability if batching is not carefully controlled. Inconsistent cement content or excessive water addition produces weak, friable renders that chalk and crack prematurely. Polymer-modified pre-bagged renders are specified where consistent performance is critical. Confirm sand specification (clean, well-graded, free of clay) and cement grade with Boral before ordering.

BGC Cement is a major supplier of ordinary Portland cement (General Purpose) in Western Australia and nationally. BGC GP cement is used for site-batched sand/cement render mixes in the same 1:4 and 1:5 mix ratios as Boral cement. BGC also produces pre-bagged render and mortar mixes (under the BGC Concrete Products range) that provide factory-controlled mix ratios as an alternative to site batching. In Western Australian strata facade remediation, BGC cement is the dominant cement supply source. The pre-bagged BGC render mixes provide consistency advantages over site-batched OPC renders while remaining at a lower cost point than polymer-modified specialist products from Sika or Mapei. Confirm current product names, mix specifications, and pre-bagged render availability with BGC before ordering.

Pre-bagged sand/cement render mixes available through Parchem Construction Supplies and Haymes trade stores provide factory-blended OPC, sand, and lime in pre-mixed dry bags that require only the addition of water on site. These products eliminate the mix ratio variability of site batching while remaining at a lower cost than polymer-modified specialist renders. In Australian Class 2 strata facade remediation, pre-bagged sand/cement renders are used on lower-specification or budget-constrained projects where polymer-modified renders cannot be justified on cost. The pre-bagged format improves QA compared to site batching but does not provide the adhesion or crack resistance improvements of polymer modification. Confirm current product names, application rates, and substrate suitability with Parchem or Haymes before ordering.