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Lime Stucco — Application Guide

How to mix, apply, and cure Lime Stucco Coarse and Fine exterior finishes over a PHL brown coat.

This Help Center article is a summary of the official Lime Stucco Application Guide. Download the full Lime Stucco Finishes Installation Guide (PDF).

Description

  • System: Part of the Earthaus BUILD (pozzolanic hydraulic lime / PHL) plaster system for natural and conventional wall assemblies.

  • Products: Lime Stucco Coarse Finish (1/4" coat, sponge-floated texture) and Lime Stucco Fine Finish (1/8" wet-on-wet, double-backed, troweled smooth).

  • Composition: Hydrated lime, pumice pozzolan, and carefully selected aggregates.

  • Purpose: Lightweight, high-performance, breathable, eco-friendly finish layers.

Safety Precautions

Hydrated lime is strongly alkaline and can cause severe injury. Follow these precautions:

  • Wear eye protection, gloves, long sleeves, and pants.

  • Wear a particle mask/respirator; do not wear contact lenses.

  • Eyes: Flush immediately with copious cold water; seek immediate medical attention.

  • Skin: Wash with cold water then mild soap; rinse with white vinegar if irritated.

  • Inhalation: Move to fresh air; stay away from dust until symptoms subside.

  • Ingestion: Do not ingest; seek medical attention immediately.

Project Planning & Preparation

Freeze/Thaw & Moisture Risk Mitigation:

  • Vulnerable zones: horizontal surfaces, the bottom ~2 ft near grade, and weather-exposed walls.

  • Optional Sealer: Apply Earthaus Breathable Sealer to reduce liquid water absorption while keeping breathability.

  • Ground clearance: Use stucco stops plus flashing to prevent wicking.

Substrate Preparation (Brown Coat Requirements):

  • Coarse Finish: The brown coat must be sponge-floated. Do not exceed 1/4" total.

  • Fine Finish: The brown coat must be sponge-floated then lightly smoothed (knock down protruding sand grains with a trowel; never leave the surface burnished or "slicked," which can cause loss of bond). Do not exceed 1/8" total.

  • Dampen the brown coat to control suction before application — dark from absorption but no visible standing water.

  • Important: Lime Stucco must not be used to fill or flatten uneven areas of the brown coat. Leveling is the brown coat's job. Applying Lime Stucco over the recommended thickness (1/4" coarse, 1/8" fine) can cause shrinkage cracking.

Mixing Guidelines

Batch Recipe: 1 bag Lime Stucco (32 lbs) + 2 gallons water (add more as needed for consistency). Add mineral pigment to the water and mix thoroughly before adding plaster; measure bulk pigment by digital gram scale.

Optimal Consistency: Soft-serve ice cream appearance — stands in a pile on the hawk and does not slide when tipped to ~30°. Avoid a runny mix; it is hard to fix.

Mortar Mixer (primary method, up to 8 bags):

Use a mortar mixer with a stationary drum and rotating paddles. A rotating-drum cement mixer is not adequate and will fail to mix Lime Stucco properly.

  1. Calculate materials: pigment = grams/bag × number of bags; water = 2 gal × number of bags.

  2. Add ~75% of the water to the mixer, then all the pigment (into the water, not on the paddles). Mix at idle ~1 minute.

  3. Increase to medium throttle and add the bags one at a time. Use a hose to wash plaster off the drum walls back into the mix — this constitutes the remaining ~25% of the water.

  4. Once consistency is soft-serve, run at full speed and mix 5 minutes.

  5. Let the mix rest 5 minutes to fully hydrate, then remix at high speed for 5 more minutes. Adjust water if needed.

5-Gallon Bucket (small batches, mixing drill):

  1. Add 2 gallons of water to a 5-gallon bucket.

  2. Add mineral pigment and mix 1 minute with a high-RPM drill.

  3. Add ~1/3 bag of Lime Stucco; mix and scrape the bucket sides. Repeat in thirds until fully incorporated.

  4. Mix 3 minutes for full pigment dispersion.

  5. Adjust with small amounts of water only if needed.

Application

Coarse Finish (~50 ft² per 32 lb bag):

  1. Dampen the brown coat.

  2. Apply a 1/4" coat evenly; maintain a wet edge; complete the entire wall at one time.

  3. Sponge float as the finish firms, using a circular motion with a clean stucco sponge float; rehydrate the float with clean water as needed.

  4. Result: a suede-like sandy texture.

Fine Finish (~100 ft² per 32 lb bag):

  1. Dampen the brown coat.

  2. Apply a wet-on-wet double-back: a first tight coat, then a second double-back coat as the first firms up (total max 1/8"). Maintain a wet edge and complete the whole wall at one time.

  3. Smooth with a clean trowel; a light mist assists. Do not over-trowel a too-dry surface ("burning" leaves black marks that are hard to remove).

  4. Allow to dry; the color lightens significantly when fully dry.

Curing

  • Keep Lime Stucco moist for at least 48 hours after application by misting. Mist morning and evening when walls are cool, once the stucco is thumbprint hard so the mist doesn't erode it.

  • In hot, sunny, dry, or windy conditions, shade with tarps and mist more often. In cool, humid conditions, misting may not be needed in the first 48 hours. Protect from direct rainfall with tarps.

  • Do not apply if temperatures could reach freezing within 72 hours of application.

Sealing

Sealing with Earthaus Breathable Sealer is optional.

  • Seal only after the Lime Stucco is fully cured (minimum 30 days). The surface must be clean, dry, and free of debris, oil, or coatings.

  • Apply with a low-pressure sprayer or roller in small areas to keep a wet edge. The sealer should be fully absorbed within ~10 minutes; avoid drips and runs.

  • Sealed stucco is dry to the touch in 1–3 hours and should be kept dry for 12 hours.

  • For very porous surfaces, a light second coat may help after 24 hours (test: water drops absorb within 3–5 minutes).

  • Avoid over-application, which can leave white residue (especially on darker finishes). It does not affect performance and dissipates over time.

Care & Maintenance

  • Cleaning: Lime Stucco is porous and may stain, especially if unsealed. Use soft brushes or microfiber cloths; for mildew or algae use a mild, pH-neutral soap diluted in water and rinse thoroughly. Avoid bleach, acids, or strong cleaners, and avoid high-pressure water — use a low-pressure rinse.

  • Inspection: Inspect annually (spring is ideal), paying attention to corners of windows, doors, and roof intersections. Hairline cracks under 1/16" are usually superficial; cracks over 1/16" may signal structural movement — address the underlying cause before patching.

  • Repairs: Minor holes, nicks, and cracks can be patched with a small batch of Lime Stucco finish, keeping the repair moist-cured for ~72 hours. Damage that extends into the brown coat, or freeze-thaw damage (spalling, friability), should be evaluated and repaired by a professional.

Calculate How Much You Need

Estimate how much Lime Stucco you need with the Lime Stucco Fine Calculator or the Lime Stucco Coarse Calculator.

Customer Support

For product questions, email [email protected]. For project-specific guidance, schedule an Earthaus technical consultation.

© 2025 Earthaus Plaster LLC

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