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Bond Plaster — Installation Guide

How to install Earthaus Bond Plaster: compatible substrates, the Edge Pull adhesion test, coat thickness, mixing, and application.

Bond Plaster is a BUILD-system product designed to adhere to substrates that are typically unsuitable for direct plaster application. Its pozzolanic hydraulic lime (PHL) formula — hydrated lime, pumice, selected aggregates, and a small amount of acrylic modifier — needs only the addition of water. It enables the BUILD Plaster System and takes the place of the PHL Binder scratch coat.

This article summarizes the official Earthaus Bond Plaster Installation Guide. Download the full Bond Plaster Installation Guide (PDF).

Compatible Substrates

Bond Plaster works on a wide range of interior and exterior substrates (always confirm with the compatibility test below). Potential substrates include, but are not limited to:

  • Cementitious backer board

  • Fiber cement board

  • Formed concrete (above grade)

  • Gypsum sheathing

  • Magnesium oxide (MgO) boards

  • Painted or sealed surfaces

  • Stucco

  • Masonry: brick and concrete block

  • Wood fiber insulation board

  • XPS foam

Safety

Hydrated lime is strongly alkaline and can cause severe injury. Eye or skin contact can cause irritation and possible irreversible tissue damage, corrosion, chemical burns, and corneal damage.

Prevention: Wear eye protection, gloves, and long sleeves and pants to prevent skin contact. Inhaling dust can cause severe upper-respiratory irritation — wear a particle mask or respirator over the nose and mouth. Do not wear contact lenses when working with hydrated lime.

If exposure occurs:

  • Eyes: Immediately flush with copious amounts of cold water and get medical attention right away.

  • Skin: Wash with plenty of cold water, then mild soap and water. If irritated, rinse with white vinegar to neutralize. If irritation persists, see a physician.

  • Inhalation: Move to fresh air and stay away until coughing and other symptoms subside.

  • Ingestion: Not intended to be ingested. Get medical attention immediately due to the alkali content.

For complete handling and hazard information, see the Bond Plaster Safety Data Sheet (SDS) (PDF).

Determine Bond Coat Thickness

As a general rule, the Bond Plaster coat should be at least half the thickness of the subsequent lime plaster layer for sufficient mechanical key and adhesion. Bond Plaster has a medium aggregate size, so thickness also depends on substrate texture:

  • 1/8 inch minimum when there is no substrate texture.

  • 1/4 inch maximum when burying texture to create a flat, even, smooth surface.

Substrate Compatibility Test (Edge Pull Test)

Always test a sample on your intended substrate first, using the masking-tape Edge Pull Test:

  1. Prepare the test area. Choose a small, inconspicuous area (or a sample of the same material), at least 6 by 6 inches. Apply masking tape to define the area, pressing all four edges firmly for clean lines.

  2. Apply Bond Plaster. Apply one coat (see thickness above). While still wet, carefully peel the tape to leave a clean-edged test section.

  3. Cure. Let the plaster fully cure and dry for 24 hours.

  4. Check the bond. Following the full guide, confirm the cured Bond Plaster is firmly adhered to the substrate and does not lift at the edge.

Project Planning & Conditions

Weather: Apply in conditions with temperatures and airflow that allow steady, even drying. Do not apply if temperatures may reach freezing within 72 hours after application.

Application sequencing: Plan the order of work for the best curing conditions, and avoid direct sun and wind.

Curing: Bond Plaster must be completely cured and dry before applying subsequent coats — at least 24 hours, depending on conditions.

Working time: Mixed Bond Plaster can be stored and reused for up to 10 days. Keep it tightly covered at room temperature or cooler so it won't dry out; remix for about a minute (add a little water if needed) to restore working consistency.

Long-term storage: Unopened Bond Plaster keeps for one year from delivery in a cool, dry location. If it gets wet and becomes chunky, it is no longer usable.

Clean-up and disposal: Let excess plaster and tool residue dry fully in the container, then remove and dispose of it in the trash.

Mixing

Tools: 1200 RPM variable-speed drill, egg-beater mixing paddle, and a 5-gallon bucket.

  1. Read through all steps before starting.

  2. Add 2 gallons of water to the 5-gallon bucket.

  3. Add 1/3 of a bag of Bond Plaster to the water, mix well, and scrape powder from the sides.

  4. Add the next 1/3, mix, scrape, and repeat until the full bag is incorporated.

  5. Mix for 3 minutes to minimize unmixed particles. Add a little water if needed to reach a soft-serve ice cream consistency.

Application

Tools: hawk, trowel, scraping knife, and a notch trowel or stucco scarifier.

  1. Read through all steps before starting.

  2. Apply a coat of Bond Plaster with a hawk and trowel in an even layer (see Determine Bond Coat Thickness).

  3. Scarify the surface while the plaster is still wet — use a notched trowel (notch depth matching the coat thickness, 1/4 or 1/8 inch) or a stucco scarifier to create texture for strong adhesion of the next coat.

  4. Let it dry. Allow Bond Plaster to cure completely before applying subsequent coats — at least 24 hours, depending on ambient conditions.

Disclaimer

This guide is provided in good faith for information only and is not legally binding. It does not exempt the user from testing and verifying the product's suitability for the intended application. Earthaus offers no additional warranty, express or implied; the buyer must test the product for suitability and assumes all associated risk. See the full guide for complete warranty and legal terms.

Copyright 2024 Earthaus Plaster LLC.

Still have questions? Email [email protected] or text 1-800-917-2414.

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