Building a stucco wall has proven to be one of the most enduring, versatile, and weather-resistant exterior wall finishes available. With its variety of colors and textures, stucco continues to be one of the most popular wall systems.
Stucco can be applied over standard, wood frame walls in a three-coat process and over masonry and poured concrete walls in a two-coat application. Before starting your project, check local building codes for wall assembly and moisture barrier requirements in your area.
A weather-resistant stucco wall requires the use of two layers of grade D waterproof building paper over the wall sheeting including plywood, OSB, exterior gypsum board and concrete board, before the application of the base coat stucco. When attaching the waterproof building paper, vertical seams should be overlapped by 6 inches or more and horizontal seams should be overlapped by 4 inches, in shingle fashion.
The building paper should also extend 16 inches around all corners. Once the water resistant building paper is in place, all trim accessories should be installed. Trim accessories can be cut to size using metal snips. Cut edges are often very sharp, so always wear gloves when working with these materials. A weep screed is a typical excess that will be required by code.
Weep screeds are installed along the bottom edges to allow any water that has entered the wall to escape. Casing beads should be installed to neatly terminate stucco at the end of the wall. Casing beads also act as a guide to help maintain a consistent stucco thickness. Casing beads, for a three coats system, should be three quarters of an inch thick.
Casing beads for use in a two-coat system over masonry or concrete should be 1/2 inch thick. Then, galvanized expanded metal lath or 1 inch woven wire stucco netting is installed over the entire surface, overlapping by one inch on the horizontal seams and two inches on the vertical seams. Galvanized nails or staples should be used every six inches, both vertically and horizontally.
Make sure that the nails or staples penetrate the studs a minimum of one inch. The lath or stucco netting should also extend 16 inches around all corners. If the base coat stucco is applied to a clean unpainted concrete or masonry surface, waterproof building paper and metal lath are not required.
Then, control joints should be placed to create wall panels no larger than 144 square feet, keeping the panels as square as possible. Stucco will shrink as it hardens and cures. Control joints help reduce the potential for shrinkage cracking. Expansion joints are required anywhere there are existing wall expansion joints and at inside corners and changes in substrate.
Expansion joints are designed to allow for the expansion and contraction of the stucco wall panels with changes in temperature. Corner trim should be used on all outside edges, to protect the exposed stucco and to provide clean finished lines. Now that the substrate is properly prepared, it is ready for the base coat stucco application. QUIKRETE Base Coat Stucco and QUIKRETE Base Coat Stucco with Water-Stop are recommended for use in a traditional three coats system over wood sheeting and as the base for a two coat application over masonry or concrete.
These pre-blended stuccos are extremely workable for hand applied stucco applications and have the high bond strength required for a successful project. Mix the base coat stucco to a workable consistency. The proper consistency is achieved when the stucco will hang on a trowel held at a 90 degree angle. Stucco that is mixed too wet will sag. Stucco that is mixed too dry will not adhere properly to the metal lath.
One bag of 80 pound base coat stucco will cover about twenty seven square feet at three-eighths of an inch thick. Using a square trowel, held at a 45 degree angle, apply the base coat stucco using firm trowel pressure to force the stucco into the lath. Work from the bottom of the wall up and apply at a thickness of about three-eighths of an inch over the entire area.
Then, using a straight edge or darby, screed the stucco to a uniform depth of 3/8 of an inch thick. Once the stucco has become thumb print hard, scratch horizontal grooves, 1/8 of an inch deep, into the base coat, across the entire area with a raking tool. This is why this step is commonly referred to as the scratch coat. Allow the scratch coat to cure for 24 to 48 hours.
Keep the surface of the stucco damp with a fine water mist. This step will help reduce shrinkage cracking, especially in hot dry conditions. Now, mix and apply another 3/8 inch layer of base coat stucco directly to the scratch coat. This step is called the brown coat. Using a straight board or darby, screed the brown coat surface to a true even 3/8 inch thickness.
Fill any surface boards with additional base coat. The total combined base coat depth should be three-quarters of an inch thick. As soon as the stucco has lost its sheen, float the surface uniformly. Then, cure the base coat with a fine water mist for 24 to 48 hours. For two-coat applications over masonry block walls and poured concrete walls, the scratch coat step is eliminated from the process. Simply dampen the wall.
Apply the brown coat. Then, screed and float the surface to a uniform 3/8 inch thickness. Now that the base coat is complete, QUIKRETE Finish Coat Stucco can be used to provide numerous decorative color and texture options for your stucco wall. Finish Coat Stucco is available in both white and gray formulations and can be combined with more than 20 standard QUIKRETE Stucco & Mortar colors. Popular textures, such as heavy lace, light lace, dash, sand float and smooth finishes are easy to achieve with a little practice.
Working from the bottom of the wall to the top, apply a consistent 1/8 inch thick coating of Finish Coat Stucco. Then, use a whisk brush to lightly dash finish coat stucco onto the wall. Then, use a trowel to knock down and flatten the stucco. If you prefer a heavier texture, first spread the finish coat stucco in a thin application to achieve good color coverage, and then, double back with a heavier uneven application.
Once the heavy coat begins to harden knock the finish down with a trowel, creating a heavy lace finish. If a smooth finish is your preference, simply use a trowel or sponge float in a circular motion. It is important to complete the entire wall in one application. This will help limit any color inconsistencies from batch to batch. Then, keep the surface damp for several days by applying a fine water mist.
Attach two layers of Grade D, waterproof building paper using galvanized nails or staples in a shingled fashion over the wall sheathing extending 16 inches around all corners.
TIP: vertical seams should be overlapped by 6 inches and horizontal seams should be overlapped by 4 inches.
Install trim accessories.
TIP: trim accessories can be cut to size using metal snips but are often very sharp, so always wear gloves when working with these materials.
Install casing beads.
TIP: casing beads for a 3 coat system should be 3/4 inch thick; casing beads for a 1 or 2 coat system should be 1/2 inch thick.
Install a galvanized, self-furring, expanded metal lath or 1” woven wire stucco netting over the entire surface also extending 16 inches around all corners. The lath or stucco netting should over-lap by 1” on the horizontal seams and 2” on the vertical seams.
NOTE: galvanized nails or staples should be used every 6 inches both vertically and horizontally and should penetrate the studs a minimum of 1 inch.
Place control joints to create wall panels no larger than 144 square feet. Keep the panels as square as possible.
Place expansion joints anywhere there exists wall expansion joints.
Install corner trim on all outside edges to protect the exposed stucco and to provide clean finished lines.
Mix the base coat stucco to a workable consistency.
NOTE: the proper consistency is achieved when the stucco will “hang” on a trowel held at a 90 degree angle – stucco that is too wet will sag; stucco that is too dry will not adhere properly to the metal lath.
Apply the base coat stucco using a square trowel held at a 45 degree angle. Use firm trowel pressure to force the stucco into the lath. Work from the bottom of the wall up and apply at a thickness of about 3/8 inch over the entire area.
NOTE: for one coat stucco systems, apply QUIKRETE One Coat Fiberglass Reinforced Stucco in a single application at ½ inch thick.
Screed the stucco to a uniform depth of 3/8 inch using a straight edge.
Scratch 1/8 inch deep horizontal grooves into the base coat with a raking tool once the stucco has become thumb-print hard.
Cure the scratch coat for 24 to 48 hours.
Mix and apply another 3/8 inch layer of base coat stucco directly to the scratch coat.
Screed the surface using a straight board or darby to 3/8 inch thickness and fill any surface voids with additional base coat. The total combined basecoat depth should be 3/4 of an inch thick.
Float the surface uniformly once the stucco has lost its sheen using a wooden trowel and cure the base coat with a fine water mist for 24-48 hours.
Apply a 1/8 inch thick coating of QUIKRETE Finish Coat Stucco in the preferred application working from the bottom of the wall to the top. Complete the entire wall in one application.
NOTE: it is important to keep the surface damp for by applying a fine water mist over several days.
Fill all control joints, expansion joints and gaps with a backer rod and QUIKRETE non-sag Polyurethane Sealant.
For more project ideas just like this, visit QUIKRETE.com.
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