BUILD Plaster System for exterior Cob

Earthaus BUILD is an innovative pozzolanic hydraulic lime (PHL) plaster system designed for application over cob construction. Earthaus BUILD Plasters are made with US-sourced natural materials and provide a high-performance, eco-friendly solution for breathable exterior and interior plaster finishes.

BUILD Plaster System for interior Cob

The Earthaus BUILD Plaster System is formulated to support the unique requirements of cob construction. BUILD plasters offer exceptional durability to protect cob walls, while maintaining breathability and allowing moisture to release, thus reducing the risk of mold and structural issues. In addition, the slow, steady strength gain of pozzolanic hydraulic lime can accommodate for early structural movement which reduces the potential for cracking.

The BUILD Plaster System for cob is standardized, yet versatile enough to be modified based on the specific needs of each project.

BUILD Plaster for Cob Guide

BUILD Materials

PHL Binder (Pozzolanic Hydraulic Lime)

Scratch + Brown Base Coats

Made with hydrated lime and pumice pozzolan, Earthaus PHL Binder creates a breathable and functional base coat plaster system that is strong yet flexible. The “pozzolan” in PHL Binder refers to the ancient Italian name for volcanic materials that react with lime to create a strong cementitious mix. PHL Binder requires the addition of locally sourced sand aggregate to improve structural integrity, increase its volume, and to reduce shrinkage during drying. Sand aggregate can be sourced at sand and gravel yards, landscape materials suppliers, and stucco and masonry supply yards. A thorough guide to sourcing local sand is provided in the PHL Binder Installation Guide.

BUILD | PHL Binder Installation Guide
BUILD | Tools & Equipment Guide

SCRATCH COAT | PHL Binder

The 3/8" PHL Binder scratch coat functions to create a mechanical bond to the substrate and give texture (tooth) for the brown coat. The scratch coat is horizontally scratched ¼” deep with a scarifier tool.

Size : 50 lbs / bag
Cost: $45 / bag
Coverage: 75 ft², may vary based on the condition of the substrate
Added Sand: Three 5-gallon buckets of sand aggregate to one bag of PHL Binder

BROWN COAT | PHL Binder

The 1/2" PHL Binder brown coat functions to build the plaster to a uniform level and create the final shape of the walls.

Size : 50 lbs / bag
Cost: $45 / bag
Coverage: 75 ft²
Added Sand: Five 5-gallon buckets of sand aggregate to one bag of PHL Binder

Go to the PHL Binder Calculator and enter Cob + project square footage to calculate the quantity of PHL Binder needed for a project. The calculator will show calculations for both scratch and brown coat quantities.

LIME STUCCO FINISHES (TWO TEXTURE OPTIONS)

Fine & Coarse Finishes

Earthaus Lime Stucco Finishes are made with hydrated lime, pumice pozzolan, and carefully selected aggregates. Lime Stucco requires the addition of water and mineral pigment color is optional. Lime Stucco Fine and Coarse Finishes are formulated to be applied over Earthaus PHL Lime Binder base coats, but may be used over other base coat systems.

BUILD | Lime Stucco Installation Guide
BUILD | Tools & Equipment Guide

FINE FINISH

Aesthetic: Smooth and refined texture, smooth from a distance

Application: Lime Stucco Fine Finish is applied as a ⅛” wet-on-wet, “double backed” coat and is troweled smooth to achieve a fine smooth texture. Lime Stucco Fine Finish can be pigmented in any Earthaus Palette or a Custom Color.

Size: 32 lb / bag
Cost: $50 / bag
Coverage: 100 ft²

COARSE FINISH

Aesthetic: Sandy texture, suede from a distance

Application: Lime Stucco Coarse Finish is applied in a single ¼” coat and typically finished with a sponge float to achieve the coarse sandy texture. Lime Stucco Coarse Finish can be pigmented in any Earthaus Palette or a Custom Color.

Size: 32 lb / bag
Cost: $45 / bag
Coverage: 50 ft²

Go to the Fine Finish Calculator or Coarse Finish Calculator, and enter your project square footage + color to calculate the quantity of Lime Stucco needed for your project.

PIGMENT OPTIONS

Bulk Mineral Pigment or Mineral Pigment Packs

Fine & Coarse Lime Stucco Finishes can be pigmented in any standard Earthaus Palette color or tinted in Custom Color

Color Palette
Custom Color

Bulk Mineral Pigment

Available by the pound, bulk mineral pigment is measured by weight. Color recipe is provided for a single bag of Lime Stucco.

Pigment names are different than Color Palette names. Click here to see a visual representation of our 12 Mineral Pigments.

Cost: $15 / pound

Mineral Pigment Pack

Mineral Pigment Packs are pre-measured packets of pigment and are mixed in, one per bag of Lime Stucco

Cost: $15 - $35, depending on the color

Both Bulk Pigment + Mineral Pigment options will show in Lime Stucco Finish Calculators.

Frequently Asked Questions

Breathability: Lime plaster allows moisture to evaporate, preventing water buildup and reducing the risk of mold and mildew. This breathability helps maintain the integrity of the cob walls.
Durability: Lime plaster provides a tough, long-lasting finish that can withstand weathering and physical wear. It hardens over time, becoming more resilient and durable.
Flexibility: Unlike some rigid materials, lime plaster is flexible enough to accommodate the natural expansion and contraction of adobe walls, reducing the risk of cracks and damage.

Water Resistance: Lime plaster acts as a protective barrier against rain and moisture. While it is not completely waterproof, it significantly reduces the amount of water that penetrates the adobe, preventing erosion and structural weakening.
Breathability: One of the most crucial properties of lime plaster is its breathability. It allows moisture that does enter the walls to evaporate, preventing water buildup inside the cob. This reduces the risk of mold, mildew, and structural damage caused by trapped moisture.
Flexibility and Movement Accommodation: Lime plaster can expand and contract with temperature changes and structural movements without cracking. This flexibility helps protect the cob from damage caused by thermal expansion and contraction or minor settling and shifting.
UV Protection: Lime plaster provides a degree of protection against ultraviolet (UV) rays. UV rays can degrade materials over time, but lime plaster helps shield the underlying cob from this damage, prolonging the life of the walls.
Thermal Regulation: Lime plaster adds to the thermal mass of cob walls, helping to regulate temperature changes. It absorbs heat during the day and releases it slowly at night, contributing to a more stable indoor climate and reducing the stress of extreme temperature fluctuations on the cob.
Resistance to Biological Growth: The high pH level of lime plaster makes it naturally resistant to the growth of mold, mildew, and fungi. This property helps maintain a healthier indoor environment and protects the structural integrity of the cob.
Wind and Erosion Protection: Lime plaster provides a durable outer layer that shields adobe walls from wind erosion and abrasion. This is particularly important in exposed locations where wind-driven particles can cause significant wear over time.