Lime Plaster Mix Calculator

How to use: Introduction: How this lime plaster mix calculator works

Lime plaster is commonly mixed from lime putty (or a lime binder), sand/aggregate, optional fiber (straw, hair, cellulose, etc.), and water for workability. This calculator converts your wall area and coat thickness into a required wet plaster volume, then splits that volume by your chosen volumetric “parts” ratio (e.g., 1 : 2 : 0.1 : 0.6).

1) Total wet plaster volume

Thickness is entered in centimeters and converted to meters:

V = A × t where A is area (m²) and t is thickness (m).

2) Split volume by mix “parts”

Your lime/sand/fiber/water inputs are treated as volume parts:

• Total parts = p_lime + p_sand + p_fiber + p_water
• Ingredient volume = V × (p_ingredient / Total parts)

3) Convert volumes to estimated masses (kg)

To give a practical shopping/handling estimate, the calculator applies typical bulk densities (these vary in real life):

Mass (kg) = ingredient volume (m³) × density (kg/m³).

Interpreting the results

• Total volume is the wet plaster volume needed for one coat at the specified thickness.
• Ingredient volumes help you measure by buckets/scoops (since “parts” are volumetric).
• Ingredient masses are estimates that help when buying materials by weight (bags) or checking handling loads.

If you plan multiple coats, run the calculator for each coat thickness (scratch/brown/finish) and add totals.

Worked example

Given: area A = 10 m², thickness = 2 cm (0.02 m), ratio = 1 lime : 2 sand : 0.1 fiber : 0.6 water.

1. Total volume: V = 10 × 0.02 = 0.20 m³
2. Total parts: 1 + 2 + 0.1 + 0.6 = 3.7
3. Lime volume: 0.20 × (1/3.7) = 0.054 m³ → mass ≈ 0.054 × 1400 = 76 kg
4. Sand volume: 0.20 × (2/3.7) = 0.108 m³ → mass ≈ 0.108 × 1600 = 173 kg
5. Fiber volume: 0.20 × (0.1/3.7) = 0.0054 m³ → mass ≈ 0.0054 × 50 = 0.27 kg
6. Water volume: 0.20 × (0.6/3.7) = 0.032 m³ → mass ≈ 0.032 × 1000 = 32 kg (~32 L)

Use these as starting points—especially water, which is typically adjusted during mixing to match sand moisture, suction, and desired consistency.

Typical ratios by coat (quick comparison)

These are not universal prescriptions—follow manufacturer guidance for NHL, hydrated lime, lime putty, and any pozzolans or additives you use.

Assumptions & limitations

• Volumetric parts: “Parts” are treated as volume parts, not weight parts.
• Typical densities: Mass estimates use generalized bulk densities; real values vary with sand grading, moisture, compaction, lime type, and fiber type.
• Water is not fixed: Water demand depends heavily on sand moisture, suction of the substrate, temperature, and desired workability. Treat water output as a starting estimate.
• Wastage not included: Spillage, remixing, uneven substrates, and tool losses can add 5–20% (or more). Consider adding a contingency in practice.
• One-coat volume: Results correspond to one coat at the specified thickness. Multi-coat systems should be calculated per coat and summed.
• Site conditions matter: Lime curing (carbonation) depends on humidity, temperature, and airflow. The calculator does not model curing time, shrinkage, or cracking risk.
• Safety note: Lime is alkaline—use appropriate PPE and follow product SDS guidance.

Formula: how the estimate is built

The result can be read as result = f(a, b, c), where those inputs represent Wall area (m²), Plaster thickness (cm), Lime parts. Keep money, time, distance, percentage, and count fields in the units requested by the form.