Stucco enhances the appearance of exterior walls. The technique is widely used in the American West and Southwest for a Mediterranean or Spanish look. The thickly applied cement-based plaster covers defects in the substrate wall and provides visual interest with different types of textures. Stucco wall finishing is easily done over plywood and is a project well within the capabilities of most handyman homeowners. Stucco application requires a few simple tools and minimal construction skills.
Build an exterior wall with only the straightest 2 by 4s for studs to avoid wall ripples and later cracked stucco. Screw or nail sheets of plywood onto the wall as underlay to support up to 7/8 inches or more of stucco. Keep the plywood dry during construction. Space the fasteners at 4 inches apart on the ends, 8 inches on the studs. Leave a 1/8-inch gap around the wood panel's edges to accommodate expansion and contraction.
Cover the panels with heavy-duty, water-resistant Grade D kraft building paper or #15 asphalt impregnated felt to protect them from moisture. Staple the paper or felt firmly onto the wooden sheathing. Repair any tears or perforations in the covering. Use two layers of covering in areas prone to heavy rainfalls. Overlap the paper as flashing around windows and doors to keep water out. Install stucco mesh or netting over the covered panels. Take care not to rip the covering.
Buy stucco pre-bagged and mix according to the manufacturer's directions. Make your own stucco by mixing 1 cubic-foot of Portland or masonry cement , 3 cubic-feet of coarse plaster sand and 4 to 7 gallons of water. Blend the mixture until there are no clumps left, in a cement mixer filled to 70 percent capacity. Put the water in the mixer first, followed by the cement and the sand. Add hydrated lime, fly-ash or chemical plasticizer to help the stucco adhere to the plywood substrate.
Mix the stucco to the consistency of toothpaste. Test the stucco and adjust the water and mix levels if the stucco is too runny or thick. If it runs off a trowel held at less than 40 degrees, it's too soupy. Transfer the stucco to wheelbarrows and wheel it over to the wall. Put the water for the next batch in the mixer between loads to prevent dried and caked stucco.
Load up a finishing pan or palette-like hawk tool with 2 to 3 quarts of stucco. Slather the stucco onto the wall in thick layers with a trowel or 12-inch finishing knife. Smooth out the stucco with long, even strokes. Press down hard to compress the stucco to remove air bubbles and fill voids in the substrate. Put pressure on the trowel and hold the upper edge 2 inches above the wall. Use decorative curved strokes or experiment with different textures to suit your tastes.