This Help Center article is a summary of the official Earthaus Light Straw Clay Wall System Guide. Download the full Light Straw Clay Wall System Guide (PDF).

Overview

The Earthaus BUILD Pozzolanic Hydraulic Lime (PHL) Plaster System is designed for light straw clay construction. It is standardized but flexible for unique project requirements.

Key Properties:

Specialized formulas with high-plasticity lime and pumice pozzolan.
Breathable plaster system allows light straw clay to release moisture.
Slow and steady curing supports flexibility and reduces cracking.

Exterior System (Light Straw Clay Walls):

Layer	Product	Thickness	Coverage
Scratch Coat	PHL Binder	3/8" (1 coat)	65 ft²
Brown Coat	PHL Binder	3/8" (1 coat)	75 ft²
Finish Option 1	Lime Stucco Coarse	1/4" (1 coat)	50 ft²
Finish Option 2	Lime Stucco Fine	1/8" (1 coat)	100 ft²
Sealer (optional)	Breathable Sealer	–	TBD

Interior System (Light Straw Clay Walls):

Layer	Product	Thickness	Coverage
Scratch Coat	PHL Binder	1/4" (1 coat)	100 ft²
Brown Coat	PHL Binder	3/8" (1 coat)	75 ft²
Finish Option 1	Sand Finish	1/8" (1 coat)	100 ft²
Finish Option 2	Stone Finish	1/16" (1 coat)	250 ft²
Sealer (optional)	Olive Oil Soap Sealer	–	700 ft²

Substrate Preparation

Inspect the Walls — Check for cracks, holes, and uneven areas. The surface must be clean and dust-free.
Ensure Walls Are Fully Dry — Light straw clay must be completely dry before plastering.
Dampen Walls Before Plastering — Pre-dampen with a fine mist immediately before plastering; the goal is moist/darkened with no standing water.
Plaster Stops & Lath — Protect dissimilar materials with felt paper plus expanded metal lath. Recommended: embed fiberglass reinforcing mesh in the brown coat to reduce cracking.
Protect Surrounding Areas — Mask windows, doors, and non-plaster elements.

PHL Binder Installation

Scratch Coat:

Thickness: 3/8". Scarify horizontally 1/4" deep while wet.
Cure 10 days before applying the brown coat.

Brown Coat:

Thickness: 3/8". Cure 10 days before applying finish coats.

Sand Aggregate (Mandatory):

Scratch coat: 1 bag PHL Binder + 3 × 5-gal buckets sand.
Brown coat: 1 bag PHL Binder + 5 × 5-gal buckets sand.

Applying the Finish Coat

After the brown coat has cured (10 days), apply your selected finish from the system table above:

Exterior finishes (Lime Stucco Coarse or Fine): see the Lime Stucco — Application Guide.
Interior finishes (Sand or Stone): see the Interior Sand & Stone Finishes application guide.

Pigment color and optional sealer are listed in the system table above.

Calculate How Much You Need

Estimate the materials for your project with the Earthaus calculators:

PHL Binder (scratch & brown coats): PHL Binder Calculator — select your wall system in the calculator.
Exterior finish: Lime Stucco Fine Calculator or Lime Stucco Coarse Calculator.
Interior finish: BUILD Sand Finish Calculator or BUILD Stone Calculator.

Technical Support

Product questions: email support@earthausplaster.com
Technical consultation: Earthaus technical consultation