This Help Center article is a summary of the official Earthaus Straw Bale Wall System Guide. Download the full Straw Bale Wall System Guide (PDF).
Overview
The Earthaus BUILD Pozzolanic Hydraulic Lime (PHL) Plaster System is designed for straw bale construction. It is standardized but versatile enough to be modified for project-specific needs.
Key Properties:
Specialized plaster formulas with high-plasticity lime and pumice pozzolan.
Breathable plaster system allows straw to release moisture, reducing mold and structural risks.
Slow, steady curing supports structural flexibility and lowers cracking probability.
Exterior System (Straw Bale Walls):
Layer | Product | Thickness | Coverage |
Scratch Coat | 3/8" (1 coat) | 65 ft² | |
Brown Coat | PHL Binder | 1/2" (1 coat) | 65 ft² |
Finish Option 1 | 1/4" (1 coat) | 50 ft² | |
Finish Option 2 | 1/8" (1 coat) | 100 ft² | |
Sealer (optional) | – | TBD |
Interior System (Straw Bale Walls):
Layer | Product | Thickness | Coverage |
Scratch Coat | PHL Binder | 3/8" (1 coat) | 65 ft² |
Brown Coat | PHL Binder | 1/2" (1 coat) | 65 ft² |
Finish Option 1 | 1/8" (1 coat) | 100 ft² | |
Finish Option 2 | 1/16" (1 coat) | 250 ft² | |
Sealer (optional) | – | 700 ft² |
Straw Bale Substrate Preparation
Bale Inspection and Adjustment — Walls must be stacked tightly, plumb, and straight. Pack voids with loose straw for uniform density. Even out undulating walls by applying additional plaster coats with 10 days of curing between each (not one thick pass).
Trimming and Shaping — Remove debris and use a chainsaw or weed trimmer to create an even surface.
Check Moisture Levels — Bales must be dry before plastering. Target moisture content: below 18%.
Dampen Before Plastering — Pre-dampen the straw with a fine mist; the goal is moist/darkened, not saturated.
Plaster Stops & Lath — Protect wood with felt paper plus expanded metal lath. Recommended: embed fiberglass reinforcing mesh in the brown coat to reduce cracking.
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: 1/2". Cure 10 days before applying finish coats.
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 [email protected]
Technical consultation: Earthaus technical consultation
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