Cement-Lime Renders: Binder Basics

Cement-lime renders are among the oldest dry-mix products and still among the most sensitive to small changes in the binder package.

What Each Component Does

Lime improves workability, water retention and flexibility, and it lets the render accommodate slight movement. Cement provides strength and water resistance.

The polymer powder adds adhesion to the substrate and cohesion inside the render. Without it, a lime-rich mix dusts and a cement-rich mix shrinks.

Choosing the Grade

A hard grade suits renders that have to be painted or skimmed and need surface cohesion. A flexible grade suits renders over insulation or on substrates that move.

Water repellency is a separate decision. In exposed facades a hydrophobic grade or a silane additive earns its cost; in sheltered interior work it does not.

Application Variables

Thickness, curing and suction decide more of the outcome than the binder does. A render cured too fast never develops its full strength, whatever the formulation.

Two coats with a scratch key between them behave better than one thick coat, and both need damp curing in the first days.