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Wood Fiberboard Interior Wall System Guide

Layer-by-layer specs, accessories, and substrate prep for finishing interior wood fiberboard panels with the Earthaus Bond Plaster system — a drywall replacement.

This Help Center article is a summary of the official Earthaus Wood Fiberboard Interior Wall System Guide. Download the full Wood Fiberboard Interior Wall System Guide (PDF).

Overview

This guide covers the Earthaus interior plaster system over wood fiberboard insulation panels (such as STEICO, GUTEX, TimberHP, or Hempitecture PlantPanel). The system applies Earthaus lime plaster finishes directly over the rigid wood fiber board, replacing traditional drywall finishing. The interior system is gauged thinner than the exterior Wood Fiberboard system and uses Sand Plaster and Stone Plaster finishes rather than Lime Stucco.

Key Properties:

  • Bond Plaster bonds mechanically and chemically to the wood fiber surface; alkali-resistant fiberglass mesh embedded across the full field reinforces the entire surface, including board joints.

  • A highly vapor-open system that preserves the breathability of the wood fiberboard, letting the wall assembly manage moisture rather than trap it.

  • Slow and steady curing allows flexibility during early structural movement and reduces cracking.

Interior System (Wood Fiberboard):

Layer

Product

Thickness

Coverage

Prep Coat (corners and fills)

Bond Plaster

Thin skim

–

Bond Coat (with fiberglass mesh)

Bond Plaster + fiberglass mesh

1/8" notch

100 ft²

Brown Coat

Sand Plaster (pigmented)

1/8"

100 ft² (one bag covers both Sand coats)

Finish option 1

Sand Plaster (pigmented)

1/32"

see Brown Coat

Finish option 2

Stone Plaster (pigmented)

1/16"

250 ft²

Sealer (Stone Finish)

Olive Oil Soap Sealer

1 coat

700 ft²

The brown coat is pigmented to match the finish color. Stone Finish is applied in place of the Sand Finish coat, directly over the brown coat. Total system thickness is approximately 1/4" with Sand Finish, 5/16" with Stone Finish. Sand Finish is matte, unsealed, and breathable; Stone Finish is low-sheen, wipeable, and soap-sealed. Neither finish is suitable for showers or wet areas.

Accessories

  • PVC mesh corner bead (outside corners) — a PVC nose with alkali-resistant fiberglass mesh wings provides impact resistance and a clean, straight edge. Example products: Trim-Tex 2209MESH (10' lengths, PVC with 4.5 oz fiberglass mesh wings) or Plastic Components via Warehouse Bay (Item 34-2209MESH, 8' lengths).

  • 4" fiberglass mesh tape (inside corners) — self-adhesive is not required; Bond Plaster provides adhesion. Example product: Saint-Gobain FibaTape (4" x 100' roll, 4.5 oz fiberglass mesh).

  • Fiberglass mesh (field) — alkali-resistant, minimum 4.5 oz/yd², embedded in the Bond Plaster field coat. Example product: EIFS Fiberglass Mesh, 4.5 oz., 38" x 150' (Warehouse Bay Item 94-38155).

  • No casing bead or weep screed — the interior system terminates by butting directly to adjacent materials (ceiling, trim, door frames).

Wood Fiberboard Substrate Preparation

  1. Inspect the Boards — Boards must be properly fastened to framing, structurally sound, clean, dry, and free of dust or contaminants. Wood fiberboard sheds fine fiber dust during cutting and handling: brush or vacuum thoroughly before plastering, as loose surface fiber under Bond Plaster is a debonding risk.

  2. Fill Cap Washer Divots — Where large cap washers are used to fasten boards to framing, fill divots flush with Bond Plaster so the surface is flat. Allow to dry fully before field coat application.

  3. Protect Surrounding Areas — Mask adjacent trim, flooring, and ceiling surfaces. Bond Plaster splatter is difficult to remove from porous adjacent materials.

Bond Plaster Installation Over Wood Fiberboard

See the Bond Plaster Installation Guide for additional reference.

  1. Install PVC Mesh Corner Bead (Outside Corners) — Apply a thin bed of Bond Plaster to outside corner areas. Press PVC mesh corner bead directly into the wet Bond Plaster. Embed and cover mesh wings completely by troweling from corner outward. No staples required. Use full-length pieces wherever possible; adjoin pieces by abutting PVC to PVC and overlapping mesh tails. Offset butt joints from substrate joints.

  2. Reinforce Inside Corners — Apply Bond Plaster to both sides of all inside corners. Fold and embed 4" fiberglass mesh tape into the wet Bond Plaster. Cover completely and create a clean inside corner.

  3. Fill Cap Washer Divots — If applicable, fill any remaining cap washer depressions flush with Bond Plaster. Allow all prep work (Steps 1–3) to dry completely before proceeding to the field coat.

  4. Apply Bond Plaster Field Coat — Using a 1/8" x 1/8" square notch trowel, work in vertical sections approximately 3 feet wide, corresponding to the width of the mesh. Apply Bond Plaster to one section in even passes. Coverage: approximately 100 ft² per bag.

  5. Embed Fiberglass Mesh — Immediately embed alkali-resistant fiberglass mesh (minimum 4.5 oz/yd²) into the wet section, then move on to the next section. Overlap field mesh joints minimum 2". At corners, lap the field mesh at least 1" onto the mesh wings of the corner bead and the inside-corner tape; do not carry mesh over the PVC nose itself.

  6. Finish Flat and Smooth — Trowel the surface flat and smooth. Unlike the exterior system, the interior Bond coat does not receive a second scarification pass. The finished surface should be even and free of ridges.

  7. Dry and Scrape — Allow the Bond coat to dry completely. Once dry, scrape any ridges or high spots. Clean up inside and outside corners. The goal is a smooth, clean surface for the Sand Plaster brown coat.

Brown Coat Installation

Apply Sand Plaster, pigmented to match the finish color, at 1/8" thickness over the dry Bond Plaster. No primer is needed; the Bond Plaster surface provides adequate adhesion. Apply in a single pass with hawk and trowel. Finish flat and smooth with as few trowel lines and blemishes as possible. This is critical: the thin finish coats will telegraph any imperfections in the brown coat surface. Allow the brown coat to dry completely before applying the finish coat. One bag of Sand Plaster covers approximately 100 ft² across both the brown coat and a Sand Finish coat.

Applying the Finish Coat

  • Sand Finish (matte, unsealed, breathable): apply pigmented Sand Plaster at 1/32" over the dried brown coat.

  • Stone Finish (low-sheen, wipeable, soap-sealed): apply pigmented Stone Plaster at 1/16" directly over the dried brown coat, wet-on-wet in a double-back application. No pigmented Sand Finish coat is applied beneath Stone. Seal with Earthaus Olive Oil Soap Sealer: 1 part Soap to 8 parts warm water, applied bottom-up, excess wiped with a clean cloth, additional coats for increased sheen.

Neither finish is suitable for showers or wet areas. See the Interior Sand & Stone Finishes application guide for complete mixing and application details.

Calculate How Much You Need

Quantities for this system are calculated per 100 ft² of wall area. Coverages may vary based on application of thicker or thinner coats and on the condition of the substrate.

  • Bond Plaster: 1 bag per 100 ft²

  • Sand Plaster: 1 bag per 100 ft² (covers the brown coat and a Sand Finish coat)

  • Stone Plaster (Stone Finish option): 1 bag per 250 ft²

  • Fiberglass mesh: wall area plus 10% for overlaps

Technical Support

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