External corner reinforcement for Portland cement plaster may be fabricated from:

External corner reinforcement for Portland cement plaster may be fabricated from:

• A. Expanded metal lath with large openings
• B. Woven wire
• C. Wood lath
• D. Plastic mesh

Answer: (A)

External corners in Portland cement plaster need a stiff, bonded reinforcement that can hold the edge true and resist cracking and movement. Expanded metal lath with large openings is designed to provide that rigidity and a good key for the plaster on both sides of the corner. The large openings let the plaster grab onto the metal and lock in, creating a strong, durable corner. Woven wire is more flexible and doesn’t give the same rigid edge, so it isn’t as effective for a clean, crack-resistant corner. Wood lath is not suitable for modern Portland cement plaster because it can deteriorate and doesn’t provide the needed rigidity. Plastic mesh lacks the stiffness required for exterior corners and can deform or crack under weather and movement.

External corners in Portland cement plaster need a stiff, bonded reinforcement that can hold the edge true and resist cracking and movement. Expanded metal lath with large openings is designed to provide that rigidity and a good key for the plaster on both sides of the corner. The large openings let the plaster grab onto the metal and lock in, creating a strong, durable corner.

Woven wire is more flexible and doesn’t give the same rigid edge, so it isn’t as effective for a clean, crack-resistant corner. Wood lath is not suitable for modern Portland cement plaster because it can deteriorate and doesn’t provide the needed rigidity. Plastic mesh lacks the stiffness required for exterior corners and can deform or crack under weather and movement.