How to Put Plaster on Straw Bale Walls

Using mud plaster is earth friendly and efficient.

Straw bale building is sturdy, inexpensive and energy efficient. Coating the walls with earth plaster increases the strength, durability and efficiency of the structure. It is also a simpler, less costly alternative to traditional siding and drywall installation. Plaster is made of a combination of sand, clay, water and sometimes chopped straw. Lime is added to plaster to make it waterproof. Applying plaster to straw bale walls is a relatively simple process that nearly anyone can do. With a few helpers and some handy tips, applying plaster to straw bale walls can be a snap.

Things You'll Need

• Cement mixer
• Large sifter
• Trowels
• Plaster mix
• Shovel

Instructions

1. Purchase plaster mix from an adobe supplier or a home improvement store. Buy earth plaster, also called mud or clay plaster, for the majority of the interior walls, but be sure to use lime plaster for wet areas such as kitchens and bathrooms. Use lime plaster on exterior walls also.

2. Sift the mixture to remove large particles.

3. Shovel the sifted mixture into a cement mixer. Add several handfuls of chopped straw if desired. Mix thoroughly.

4. Add water according to package instructions. Mix thoroughly once more.

5. Use a trowel to apply 1 inch of plaster to the straw bales.

6. Repeat steps 2 to 4 as needed throughout the project.

7. Allow the first coat to dry. This may take several days, and the plaster should be hard to the touch when dry.

8. Apply a second coat of plaster to create a smoother surface. Let dry.

9. Apply a third coat of plaster if you wish to add color or texture. This coat should be quite thin, as it is purely for aesthetic purposes.

10. Let the final coat dry.

Tips & Warnings

• Natural pigments can be added to plaster to create a variety of colors.

• Earth plaster remains malleable for several days, giving you plenty of time to create your desired finish.

• Using lime plaster for all coats on exterior walls will ensure a completely water-resistant surface.

• Do not use earth plaster in bathroom or kitchen areas where water is likely to come into contact with the wall surface. Use a lime plaster in these areas instead.

• Check your local building code as some areas may require that wire netting be adhered to the bales prior to plastering.

References

• Building with Awareness: Earth Plaster, Mud Plaster, and Clay Plaster
• Straw Bale Home Basics

Resources

• YouTube: Breathable Plaster Exterior for Straw Bale Homes from BGTV