How to Apply Insulating Stucco to a Masonry Wall

Stucco adds life and texture to a surface's appearance.

A masonry wall, such as one made of brick, cement or concrete, is an ideal surface for stucco. Adding stucco to such a wall provides a number of advantages, hiding irregularities or bringing a new dimension to an otherwise flat wall. It can also add an extra layer of insulation on your walls that can help to keep the heat or cold of the weather out of your home. Every stucco application will be slightly different, as the actual work of texturing is up to the installer.

Things You'll Need

• Protective eyewear
• Protective footwear
• Long clothing
• Gloves
• Solvent cleaner
• Muriatic acid
• Wall patching material
• 3/8-inch-thick wooden boards
• Masonry screws
• Drill
• Portland cement
• Lime
• Sandblasting
• Wheelbarrow or mixer
• Hose
• Trowel
• Flat edge
• Float

Instructions

1. Clean the masonry surface with mineral spirits or a similar solvent cleaner. These cleaners will remove dirt and dust, as well as any grease, wax or oil buildup on the wall. If the masonry features efflorescence, a powdery white substance, clean it with a diluted muriatic acid solution.

2. Inspect the wall for damage. If you find cracks or holes larger than ¼ inch wide, patch them with concrete, cement or epoxy patches, available at hardware and home improvement stores. Follow patch instructions carefully, as some require you to chisel out the damage while others can be applied on the crack as is. Allow all repair work to dry fully before continuing.

3. Screw 3/8-inch-thick lengths of lumber to the top and bottom of the wall. If the wall is more than 6 or 7 feet tall, attach wood across the center as well. Use masonry screws to hold the wood pieces in place. These will serve as guidelines to help you achieve a smooth, level stucco surface.

4. Mix 1 part Portland cement, 1 part lime and 4 parts fine sand in a wheelbarrow or mixer. Combine this with enough water to create a consistency of softened butter.

5. Mist the masonry wall with a hose nozzle. The surface should be damp but not soaking or dripping.

6. Spread the stucco mixture onto the wall with a flat trowel, holding the trowel at an angle between 30 and 45 degrees to achieve an even spread. Press firmly against the wall to ensure the stucco fills in the small indentations and grooves in the masonry surface.

7. Fill in the wall until the stucco is even with the boards you installed; this will give you a base coat of 3/8-inch-thick stucco.

8. Scrape a flat-edge piece of metal or wood across the surface, scraping against the wooden boards to ensure that all areas are filled uniformly to the 3/8-inch level. This will flatten the surface. Touch up any areas that you disturb and level again, repeating until you achieve a completely level surface.

9. Detach the wooden pieces from the wall by removing the masonry screws. Try to move the boards as little as possible while you take them off so that you don't mess up the stucco surface.

10. Fill in the areas left uncovered by the boards. Fill to the same level as the rest of the wall. Allow the surface to dry for an hour or so, until the stucco has lost some of its shine but hasn't dried completely.

11. Run a wooden or foam float over the stucco surface in figure-eight or circular motions. This process helps to compact the stucco and make sure there won't be any cracking as it dries. Allow this first coat to dry overnight before continuing.

12. Spread a 1/8-inch to ¼-inch top layer of stucco material over the base coat. Because this layer is so thin, you shouldn't need wooden guide boards.

13. Texture the surface according to your preference with a sponge, paintbrush or trowel. Because the base coat is dry, you will only texture the top coat and don't have to worry about creating holes or gaps that will ruin your insulation. When texturing is complete, allow the wall to dry for 24 hours before exposing the surface to moisture.

Tips & Warnings

• Stucco bonds and cures best when applied at temperatures between 50 and 70 degrees Fahrenheit.

• Try mixing small batches of stucco material first to get the hang of proper consistency. You can also use a manufactured, premixed stucco material for the wall. If the stucco mix begins to dry as you work, add a little more water.

• Cement and lime are extremely caustic and can burn skin if left on it. Wear protective gloves, footwear, goggles and long clothing when working with stucco. If you get any of the materials on your skin, wash it away immediately.

References

• Ask the Builder: Applying Stucco
• Taylor Rental: Stucco Concrete Block