Practice

Natural plaster

Also known as: Earth plaster, Lime plaster, Clay plaster

Wall and surface finishes made from earthen materials (clay, lime, sand, fiber, sometimes pigment) — without Portland cement or synthetic additives. Used historically across nearly every culture; revived alongside the natural-building movement as the appropriate finish for straw-bale, cob, earthbag, and other natural-wall systems. Provides breathability (allowing walls to manage moisture), beauty (warm-toned natural pigments and textures), low embodied carbon, and indoor-air-quality benefits. Three primary types: earth (clay-based), lime, and gypsum.

Three primary types

Earth plaster — clay + sand + fiber + water. Different recipes for base coat (more clay, more fiber, longer fiber), middle coat (intermediate), and finish coat (less clay, finer sand, finer fiber). Can be tinted with iron-oxide pigments. Soft to scratch but resilient; remoistens and self-heals minor damage.

[[lime-plaster|Lime plaster]] — slaked lime (calcium hydroxide) + sand + fiber. More durable than earth plaster; sets through carbonation (CO₂ absorption) over months. Variants include lime putty plaster, [[lime-binder|hydraulic lime]] plaster, and tadelakt (Moroccan lime+soap technique for water-resistant finishes).

Gypsum plaster — calcium sulfate-based; also natural; common in conventional finishes. Less moisture-resilient than lime or earth.

Why natural plasters matter

Breathability — allow walls to absorb and release moisture; critical for natural-wall systems where modern vapor barriers would trap moisture and rot the wall
Beauty — natural pigments produce warm, varied, alive surfaces; finger-marked, tooled, polished, or smooth-finished
Indoor air quality — no off-gassing; clay particularly is documented to absorb humidity and some indoor pollutants
Carbon — much lower embodied carbon than cement-based plaster
Repairability — earth plaster patches with rewetting; [[lime-plaster|lime plaster]] can be patched with matching mix; both vastly more repairable than synthetic finishes

Application

Hand-applied with hawk and trowel; finishes vary widely:

Float finish — smoothed with wood or sponge float; matte texture
Trowel finish — burnished smooth with steel trowel; polished sheen
Stamped or pressed finish — using leaves, fabric, or tools for relief
Rubbed finish — worked with rubbing stones for very smooth surface
Tadelakt finish — Moroccan technique; [[lime-plaster|lime plaster]] polished with smooth stones and sealed with olive-soap; produces water-resistant smooth finish for bathrooms

Sources

The Natural Plaster Book, Cedar Rose Guelberth and Dan Chiras (New Society, 2003)
Building with Cob, Adam Weismann and Katy Bryce — extensive plaster sections
Multiple natural-building technical publications

Rooted in life.

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