Applying stucco in your home is actually a simple process that requires the right tools and background. Stucco homes come with a lot of benefits like having a sturdy, weather-resistant covering for unfurnished or less attractive surfaces like concrete blocks or clay bricks.
Below are the steps professionals follow in applying exterior stucco over a steel or wooden base or over a solid wall.
Stucco over a concrete wall or masonry
Prepare the surface of the wall where you want to apply stucco. If the wall surface has a rough texture and absorbent, you can directly apply the stucco over these solid or rigid surface. Otherwise, if the wall is not absorbent, you can moist the surface with water. If you see any visible contamination, wash the surface thoroughly. Also, is the wall is too smooth like those that are covered by paint or sealer, you can apply the following treatments:
- Acid etching
- Bush hammer or roughing
- Apply bond agent
If unsure if the wall can support stucco, apply the stucco using the same process that you apply stucco over a stud wall. Attach a metal lath and plastering over it.
Make the wall surface wet. In order to improve the suction bond and lessen the amount of moisture the wall absorbs from the plaster, wet the wall surface before the stucco application. You may use a fog spray to do this. Just make sure to damp the surface and not fully soak Also, if you felt that the temperature is extreme – either very hot or cold, suspend the application as extreme weather could interfere with the curing process.
Prepare the scratch coat by mixing it. The coat must be a mixture of 1 part cement (includes lime) and 2 ¼ to 4 parts sand. Plastic cement is already pre-mixed with lime, making it the easiest to use and mix. Mix it with a dry material like plaster sand.
Apply the scratch coat. Trowel a layer of ¼ inch (6.4 mm) thick and apply this with shallow, horizontal lines. Keep the notched trowel perpendicular to the wall as you apply so that the next coat bond on the surface properly.
Wait for a few hours before applying the brown coat. But if you’re using a modern cement, you can apply the brown coat immediately. No need for a scratch coat to totally cure. Once the first layer of brown coat solidifies, normally after 4 to 5 hours, trowel on the second layer.
Maintain the proper moisture as the brown coat cures. It is important to keep the stucco moist while it’s curing, usually over the next 48 hours preceding the application.
Apply the finishing coat. This consists of the mix of 1 part cement materials and 1 ½ to 3 parts sand. You also have an option to add some colors. You can use a texture roller if you are inexperienced at applying with textured finishes.
Stucco over a stud wall
Check if the weather is ideal for applying stucco in a stud wall. The ideal weather should be between temperatures of 50 degrees to 50 to 60ºF (10–16ºC). Postpone the working the temperature rises above 90ºF (32ºC) or drop below 40ºF (4ºC).
Place the sheathing materials. The most common surfaces for stucco are oriented strand board, cement board, exterior grade gypsum sheathing, and plywood.
Cover the plywood with any of the following – building paper, draining house wrap, or rain screen. You can also use a 15 lb per 100 square foot roofing felt or some kinds of house wrap except a plastic one because it is not designed for stucco. Lay the cover by at least 4 inches (10 cm) and secure them using roofing nails. Take note that most building codes need at least two layers of Grade D building paper or any water-resistant barrier.
Place the casing bead and weep screeds. At the corners of doors and windows, apply the casing bead as a plaster base. Meanwhile, place the weep screed at the base wall.
Fasten the metal lath. This is better done by an experienced contractor. However, you can also do it on your own. Nail the lath to the studs at not less than 7-inch intervals. Overlap the lath by at least t ½ inch (1.25 cm) on the side and inch (2.5 cm) at the end.
Install control joints wherever two different walls meet. Separate the wall into rectangular panels using control joints, with a space between them less than 18 ft (5.5 m) apart, to minimize cracking.
Combine and mix the scratch coat. Mix from 1 part cement material and 2 ¼ to 4 parts plaster sand. You need to add a hydrated lime if you are using type 1 Portland cement. Mix with sufficient water that you can trowel the stucco. Having excess water makes it prone to sagging or falling off.
Trowel the scratch coat into the lath. Put the scratch coat using a square trowel while steadily pressing it into the lath. The thickness of this layer should be ⅜ inches.
Score the scratch coat lightly. Scratch coat refers to the first coat that ensures a strong bond with the next coat.
Allow the scratch coat to cure for at least 48 hours while keeping it moist. During this stage, it is necessary to protect the stucco from being dry. That’s why sprinkling water or misting the stucco twice a day is recommended unless relative humidity is above 70%. You may also protect the wall with a sunshade if needed.
Mix the brown coat using 1 part cement and 3 to 5 parts brown coat. Apply another ⅜ inch layer of stucco and screed.
Let it cure for at least 7 days while keeping the moisture up. Note that the first 48 hours are the most important in maintaining the right moisture level. But it doesn’t mean that you won’t continue misting afterward.
Apply the finishing coat. This is the final coat that has a ⅛ inch layer. This defines the texture of your stucco wall.