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Calcimator

Natural Plaster Calculator

Lime, clay, or earthen plaster volume from wall area.

About this calculator

Total plaster volume is Wall Area times Coat Thickness times Number of Coats, so all three carry real weight, but they don't all move the same output: Number of Coats raises total material (more coats means more volume, obviously) while Coverage per Coat stays fixed at the full Wall Area, since every coat -- whether it's the first of one or the last of four -- is applied over the same whole wall. Going from the 2-coat default to 4 coats doubles Total Plaster (more passes over the same surface) while Coverage per Coat holds steady at 400 sq ft either way. Plaster Type is a coded 0/1/2 selector (clay, lime, gypsum) that changes the binder-to-sand ratio: clay uses a 30/70 split, lime a leaner 25/75, and gypsum the richest 40/60 -- switching from clay to gypsum at the same total volume raises binder volume by roughly a third (from 30% to 40% of the mix) while trimming sand volume by about a seventh (from 70% to 60%), because more of the mix becomes binder rather than aggregate.

At the default 400 sq ft wall with 0.75 in coats applied twice, that's 50 cu ft of total plaster, about 0.56 cu yd of clay binder, and 1.3 cu yd of sand. The calculator doesn't account for substrate preparation (scratch-coat keying into lath or masonry) or the extended cure time natural plasters need between coats.

Inputs

sq ft
in

Results

Total plaster (cu ft)

50

Binder (cu yd)0.56
Sand (cu yd)1.3
Coverage per coat (sq ft)400
How to Use This Calculator
  1. Enter Wall Area (sq ft) and Coat Thickness (in) per layer.
  2. Set the Number of Coats (scratch, brown, and finish coats).
  3. Select Plaster Type (clay, lime, or gypsum) to apply the correct binder ratio.
  4. Review Total Plaster (cu ft), Binder (cu yd), and Sand (cu yd) needed.
  5. Order materials in batches matching your mixing capacity to maintain consistent mix ratios.

How the result changes with Wall area (sq ft)

Wall area (sq ft)Total plaster (cu ft)
20025
30037.5
60075
1,000125

What each input means

Wall area (sq ft)
Total wall surface area to plaster.
Coat thickness (in)
Thickness of each plaster coat.
Number of coats
Scratch coat + finish coat (2 typical).
Plaster type (0=clay, 1=lime, 2=gypsum)
0 = clay plaster, 1 = lime plaster, 2 = gypsum/earthen blend.

What each result means

Total plaster (cu ft)
Total volume of plaster material for all coats.
Binder (cu yd)
Volume of clay, lime putty, or gypsum binder.
Sand (cu yd)
Volume of plastering sand.
Coverage per coat (sq ft)
Area covered by each application.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Wall area (sq ft) = 400, Coat thickness (in) = 0.75, Number of coats = 2, Plaster type (0=clay, 1=lime, 2=gypsum) = 0 = 4 input(s) provided
  2. Calculate Total plaster
    Total plaster = volPerCoat * numCoats
    50 = 50
  3. Calculate Binder
    Binder = round((totalVol * r.binder) / 27 * 100) / 100
    0.56 = 0.56
  4. Calculate Sand
    Sand = round((totalVol * r.sand) / 27 * 100) / 100
    1.3 = 1.3

Engine last updated . Checked against 4 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Is coverage-per-coat the same whether I apply one coat or four?

No. Coverage per Coat equals Wall Area regardless of Number of Coats -- every coat, whether it's coat 1 of 1 or coat 4 of 4, is applied over the full wall. What changes with more coats is Total Plaster (the total material volume across all coats), not the area any single coat covers.

What binder-to-sand ratio does each plaster type use?

Clay plaster mixes 30% binder to 70% sand, lime plaster a leaner 25% binder to 75% sand, and gypsum/earthen blend the richest at 40% binder to 60% sand -- switching types at the same total volume shifts material quantities between the binder and sand outputs without changing the total plaster volume itself.

What's a typical number of coats for natural plaster?

The calculator defaults to 2 coats (a scratch coat plus a finish coat), which is typical for many natural plaster systems, though some three-coat systems add a separate brown coat -- the input allows up to 4 coats for heavier or more textured applications.

Do coat thickness and wall area affect material volume in the same proportional way?

Yes -- Total Plaster is a direct product of Wall Area, Coat Thickness, and Number of Coats, so a given percentage increase in coat thickness raises total plaster volume by that same percentage, just as increasing wall area would.

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