Every two-component cementitious coating system is defined by a ratio: the mass of dry powder (Part A) to the mass of liquid polymer emulsion (Part B). This ratio is not a suggestion. It is the formulator's calculated optimum — the precise balance at which the cement phase and the polymer phase each contribute their intended properties to the cured composite. Deviate from it, and the material becomes something other than what was designed.
Why the Ratio Matters
The powder-to-emulsion ratio controls three critical properties simultaneously. First, it determines the water-to-cement ratio — the parameter that governs cement hydration kinetics and ultimate compressive strength. Second, it determines the polymer-to-cement ratio — the parameter that governs flexibility, adhesion, and tensile strength. Third, it determines the rheology — the workability, viscosity, and open time of the freshly mixed material.
These three properties are coupled. Increasing the liquid proportion (more emulsion relative to powder) raises the water-to-cement ratio (reducing strength), increases the polymer-to-cement ratio (improving flexibility but reducing hardness), and reduces the viscosity (making the material more fluid but potentially more prone to sagging on vertical surfaces). The formulator's specified ratio represents the point at which all three properties are optimised for the system's intended application.
System-by-System Reference
The following mixing ratios are representative of the major cementitious coating system categories. Specific products may vary; always refer to the manufacturer's technical data sheet for the exact ratio.
Microcement — Fine Sand (wall systems): Powder-to-emulsion ratio of 4:1 by weight. This higher powder loading produces a stiffer paste suited to vertical application at thin film thickness (0.1mm per coat). Pot life is approximately thirty minutes at twenty-five degrees. The material should be mixed to a smooth, lump-free paste resembling thick yoghurt.
Microcement — Coarse Sand (floor systems): Powder-to-emulsion ratio of 4:1 by weight, identical to the fine sand system but with coarser aggregate producing a more textured, robust film. Application thickness is 0.15 to 0.20mm per coat. The coarser aggregate reduces the material's tendency to self-level, requiring the applicator to establish the surface profile with the trowel.
Liquid Granite — Pattern Coat: Powder-to-emulsion ratio of approximately 3:1 by weight. The lower ratio (more liquid relative to powder) produces a material with extended workability suited to the texture-building technique that defines the system. The higher polymer content contributes to the flexibility needed in a thick, textured layer. Pot life is approximately forty-five minutes at twenty-five degrees.
Liquid Polish — Main Paint: Supplied as a ready-mixed, single-component material that requires only thorough stirring before application. No emulsion is added. The formulation is pre-balanced at the factory, ensuring consistent properties regardless of operator practice. Pot life exceeds two hours, reflecting the material's high workability and extended open time.
Opus — Body Coat: Powder-to-emulsion ratio of approximately 3.5:1 by weight. This self-levelling system requires a balance between fluidity (for levelling) and body (for thickness control). The ratio is calibrated to produce a material that flows freely when poured but maintains its applied thickness without migration.
The mixing ratio is the recipe. The material is the dish. You would not double the salt in a master chef's recipe and expect the same result. The same principle applies to cementitious coatings.
Measuring Accurately
The specified ratio is given by weight, not by volume. This distinction is critical, because the bulk density of cementitious powder differs substantially from the density of the liquid emulsion. A volume-based measurement — scoops, cups, or visual estimation — will produce a different actual ratio than intended, with unpredictable consequences for the cured film properties.
The minimum equipment for accurate measurement is a digital scale with a capacity of at least twenty kilograms and a resolution of ten grams. The powder is weighed first, then the emulsion is added incrementally until the target ratio is achieved. Alternatively, many applicators pre-weigh component quantities for each batch before beginning the work day, ensuring consistency across multiple batches.
Common Errors and Their Consequences
Too much liquid: The material flows too easily, sags on vertical surfaces, and takes excessively long to cure. The cured film is soft, weak in compression, and prone to scuffing. In severe cases, the excess water prevents complete cement hydration, producing a permanently under-cured coating.
Too little liquid: The material is stiff, difficult to spread, and prone to tearing under the trowel. The dry mix cannot hydrate fully, leaving unhydrated cement particles that contribute to efflorescence and reduced adhesion. The cured film is brittle, crack-prone, and lacks the flexibility provided by the polymer phase.
Inconsistent ratios between batches: Even when each individual batch is within an acceptable range, variation between batches produces visible differences in colour intensity, surface texture, and sheen across the finished surface. Consistency — batch to batch, day to day — is the hallmark of professional application.
The Discipline of Precision
In an industry where many variables are difficult to control — substrate condition, ambient weather, supply chain logistics — the mixing ratio is one of the few parameters that is entirely within the applicator's control. It requires no special skill, no expensive equipment, and no environmental luck. It requires only discipline: the willingness to measure rather than estimate, every time, without exception.
That discipline, more than any other single factor, determines whether the coating system achieves its designed performance or falls short of it.