OCR
Initialism of one coat render.
OCR: single-layer exterior wall finish
One coat render (OCR) is a factory-produced, pre-batched cementitious or polymer-modified coating applied in a single pass to exterior masonry, blockwork, or concrete. It combines the traditional render coat with integral finish in one operation, typically 12 to 20 millimetres thick, eliminating the need for a separate finish coat. The material arrives on site ready-mixed or in powder form requiring only water.
OCR saves labour and programme time on new build and remedial work. The binder is usually Portland cement, lime, or a blend with polymer additives that improve adhesion and crack resistance. Aggregates range from sharp sand for textured finishes to fine silica for smoother finishes. Colour and texture are added during manufacture, so site mixing is minimal and consistency across large areas is easier to control than traditional multi-coat systems.
Application and performance
OCR is typically applied by spray equipment (airless or piston pump) or hand trowel, depending on surface profile and site access. Coverage is around 1.5 to 2 kilograms per square metre per millimetre of thickness. It requires a sound, clean substrate with adequate suction; highly absorbent blockwork may need dampening beforehand to prevent premature drying and poor adhesion. Curing takes 7 to 28 days depending on formulation and weather.
The main risk is cracking due to rapid drying, thermal movement, or substrate movement. OCR is less forgiving than traditional render because there is no scratch coat to absorb minor movement. Products with higher polymer content show better crack and impact resistance but cost more. Uncoated OCR offers limited weather durability; many specifications include a topcoat of breathable masonry paint within 12 months.
OCR is now standard on low-rise residential and commercial work in the UK and Europe. It suits repetitive facades where texture consistency matters. It is less suitable for exposed coastal sites or where substrate settlement is expected, and should not be applied in freezing conditions or strong sunlight.