External corner reinforcement for Portland cement plaster may be fabricated from which material?

External corner reinforcement for Portland cement plaster may be fabricated from which material?

• A. Expanded metal lath with large openings
• B. Woven wire
• C. Plastic sheet
• D. Solid wood trim

Answer: (A)

External corner reinforcement in Portland cement plaster relies on a rigid metal mesh that grips the plaster at the corner to resist cracking and edge distortion. Expanded metal lath with large openings provides that strong, interlocking reinforcement because its stiff, perforated pattern wraps neatly around the corner and gives the plaster a solid key to bite into. The large openings also allow plaster to key through and bond effectively, helping to distribute stresses at the joint. Woven wire lath can serve as a base in some systems, but it doesn’t offer the same edge rigidity and form stability as expanded metal lath with large openings, which is why the latter is preferred for outside corners. Plastic sheets lack the stiffness and bonding characteristics needed for reinforcing cement plaster, and solid wood trim isn’t compatible with cement plaster systems and won’t provide the embedded reinforcement or durability required.

External corner reinforcement in Portland cement plaster relies on a rigid metal mesh that grips the plaster at the corner to resist cracking and edge distortion. Expanded metal lath with large openings provides that strong, interlocking reinforcement because its stiff, perforated pattern wraps neatly around the corner and gives the plaster a solid key to bite into. The large openings also allow plaster to key through and bond effectively, helping to distribute stresses at the joint.

Woven wire lath can serve as a base in some systems, but it doesn’t offer the same edge rigidity and form stability as expanded metal lath with large openings, which is why the latter is preferred for outside corners. Plastic sheets lack the stiffness and bonding characteristics needed for reinforcing cement plaster, and solid wood trim isn’t compatible with cement plaster systems and won’t provide the embedded reinforcement or durability required.