Stucco is a mix of different concretes, applied in multiple layers to provide a strong, solid bond to the wall. It has a timeless appeal as it closely resembles mud and adobe. But stucco is so much more. It is waterproof, easy to maintain, and long-lasting. Some stucco types are also affordable, earthquake resistant, breathable in humid temperatures, and attractive whether by itself or in combination with other siding materials like clapboard and brick. However, the stucco application is quite challenging as it requires meticulous preparation of the substances as well as proper knowledge in its application methods.
Prepare the substance
If you are applying stucco over an existing wall, you have to check if there is any crack or damage first as these damages may affect the result of the stucco application. If you find any crack or damage, you need to immediately repair it with fresh mortar. Also before applying the stucco, wash the wall using a power washer or scrub it using a combination of water and trisodium phosphate solution.
Prepare your plywood, OSB, or cement board sheathing. To cover the surface of your stucco project, buy enough galvanized stucco lath and galvanized fasteners.
Step by step process on how to apply stucco:
- Hang a Double Layer of Building Paper
Begin by hanging the building paper at the bottom of the wall and overlay every successive layer at least 4 inches over the one below it. Make sure that the sheets overlap by at least 6 inches once you form vertical seams. Then expand the paper around corners for at least 16 inches. Once extended, using galvanized roofing nails or staples, fasten it in place.
- Install Trim Accessories
Prepare and fasten trim accessories, such as casing beads, with galvanized nails. The weep screed is one of the trim accessories that is very important to let moisture drain from behind the stucco.
- Apply Galvanized Lath or Netting
The netting should be attached to the wall using galvanized nails or staples which are long enough to reach the studs by at least 1 inch. Allow at least 6 inches of spaces in between fasteners. Overlap the vertical seams of the lath by 2 inches while the horizontal seams by 1 inch.
Applying the Stucco
You will need two different types of stucco regardless if you are applying the stucco in a two or three coat system- the base coat formulation which is suitable for undercoats and a lighter finish coat formulation which is great for the topcoat.
Just like mixing cement, mixing a stucco is straightforward. Simply pour the contents of a bag into a wheelbarrow or mixing trough, then add water as you mix. The proper consistency is very important. Check this by trowelling your wet stucco mix and hold the trowel sideways. If the stucco mix slides off, it means that there’s too much water in the stucco mix.
- Apply and spread the Scratch Coat. Using a square trowel held at a 45-degree angle apply the scratch coat to the lath or netting. Begin applying stucco from the bottom of the wall and work your way to the top. Apply it with enough pressure to push the substance into all gaps in the netting. If there are voids or spaces, apply more.
- Spread the substance using a straight back and forth movement to flatten with a uniform 3/8-inch thickness and straight border darby or a straightedge. Wait for it to solidify. Once the material is stiff, scratch the surface using a raking tool to draw ⅛ inch deep horizontal grooves. Let this scratch coat sit for 24 to 48 hours while maintaining its surface moisture level by misting water. This may avoid shrinkage and crack.
- Apply the Brown Coat
Apply another layer of base coat on the scratch coat to a depth of ⅜ inch. Scrape it using a darby to flatten. If you find any void spaces, fill it with the material to create a smooth, flat surface. The total thickness of the material on the wall should be now 3.4 inches. Allow the brown coat to harden for a few minutes then using a sponge masonry float, smooth the surface. Once again, let it sit for 24 to 48 hours while misting to keep the necessary moisture.
If you are applying it over masonry or brick, the brown coat is the first and only base coat.
Step 3: Finish With the Color Coat
Prepare the finish stucco coat by mixing it with water referring to the same texture consistency as the base coat. You may add some stucco colorant if desired. Spread the stucco to the wall using a trowel with ⅛ inch thickness. In order to give the stucco the desired texture, use ling strokers, knife swaths, and other similar techniques. When your stucco is stiff enough, you can use a sponge trowel to flatten the surface. Mist the surface for several days to avoid cracking while it cures.