Things You'll Need
Cement fiber board
Soffit vents and covers
Stucco, three types
Rectangular mason's trowel
Garden hose or spray bottle
Stucco is a fireproof building material, which makes it an ideal coating for the horizontal soffits under eaves of a roof. Eaves are subject to catching flying embers from wildfires because windswept hot sparks are blown upward and lodge against the soffit. This is of particular concern in places such as California, where brush and wildfires often spread into residential areas. Stucco, a mixture of cement, sand and water, can be applied to the soffits of any house but obviously is best with houses that have stucco walls, a common building style in much of the Western United States.
Cover soffits with fiber cement board if they are open and not already sealed. Install soffit vents at the same time to allow air to escape from the attic. Remove soffit vent covers and staple waterproof membrane and metal lath over wood-sealed soffits. Use a construction stapler and hammer and galvanized nails to fasten these as a base for stucco.
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Spread a 3/8-inch thick layer of base or scratch coat stucco over metal lath with a rectangular mason's trowel and roughen the surface with the notched edge of the trowel. Buy a prepared brown coat stucco mix and add water according to package directions. It must be solid enough to hold in the lath, but fluid enough to spread easily. Let that coat cure 48 hours.
Put a second coat of stucco, using a prepared brown coat mix, over the scratch coat on metal lath or as a first coat on cement fiber. Run this right to the edges of the soffit and connect it to the wall stucco so no gaps exist between the soffit and wall. Smooth this coat with the straight edge of the trowel or with a board to fit between the wall and fascia or facing board on the outside of the soffit. Let this dry 24 hours.
Finish the soffit stucco -- for either lath or cement fiber -- with a final coat. Spread the final coat smooth or texture it to match the stucco on the house walls. Let it dry 24 hours and replace the soffit covers or install covers on new soffit vents.
Keep stucco moist during the curing process. Spray it lightly with water with a garden hose misting nozzle or spray bottle.