Contractor Exam Questions And

CA C35 Lathing And Plastering Contractor Exam Questions And Correct Answers (Verified Answers) Plus Rationale2026 Q&A| Instant Download Pdf

• What is the primary purpose of lath in plastering?
• To provide decoration
• To serve as a temporary support
• To provide a key for the plaster to adhere to
• To prevent moisture

Rationale: Lath provides a mechanical key that holds the plaster

firmly in place.

• Which type of plaster is typically used for exterior walls?
• Gypsum plaster
• Lime plaster
• Cement plaster
• Clay plaster

Rationale: Cement plaster is durable and resistant to weather,

making it suitable for exterior applications.

• What is the standard thickness for a single coat of interior plaster on

walls?

• 1/4 inch
• 1/2 inch
• 3/8 inch
• 1 inch

Rationale: A standard single coat is usually 3/8 inch to ensure proper

adhesion and finish. 1 / 3

• What is the function of a scratch coat in plastering?
• To provide a decorative finish
• To seal the surface
• To create a rough surface for the subsequent coat
• To waterproof the wall

Rationale: The scratch coat provides a textured surface that allows

the brown coat to bond effectively.

• Which material is commonly added to plaster to improve workability?
• Sand
• Water
• Paint
• Cement

Rationale: Water is added to achieve the correct consistency for

smooth application.

• How should lath be fastened to wood framing?
• With nails at 24-inch spacing
• With nails at 6–8 inch spacing
• With screws at 12-inch spacing
• With adhesive only

Rationale: Proper nailing spacing ensures the lath is secure and

provides adequate support for plaster.

• What is the main difference between gypsum plaster and lime plaster?
• Gypsum sets slower
• Lime plaster is non-adhesive
• Gypsum sets chemically; lime plaster sets by carbonation
• Lime plaster is only for ceilings

Rationale: Gypsum plaster sets through chemical hydration, while

lime plaster hardens through carbonation with CO₂.

• What type of lath is typically used for curved surfaces?
• Wood lath
• Metal lath
• Wire mesh lath
• Gypsum board

Rationale: Wire mesh lath is flexible and easily shaped around

curves.

• What is the recommended mixing ratio for a standard cement plaster

(cement:sand)? 2 / 3

A. 1:6

B. 1:2

C. 1:4

D. 2:1

Rationale: A 1:4 cement-to-sand ratio provides a balance of workability and strength.

• Why is it important to dampen a wall before applying plaster?
• To make plaster dry faster
• To prevent premature absorption of water from the plaster
• To reduce plaster adhesion
• To improve color

Rationale: Damping prevents the wall from sucking water out of the

plaster, which could weaken it.

• Which finish is smoother, suitable for painting?
• Scratch coat
• Finish coat
• Brown coat
• Base coat

Rationale: The finish coat provides the final smooth surface for

decoration or painting.

• What is the typical thickness of a brown coat?
• 1/8 inch
• 1/4 inch
• 1/2 inch
• 3/8 inch

Rationale: The brown coat usually provides the main body of plaster

at approximately 1/4 inch.

• Which plastering method is used on masonry block walls?
• Spray gypsum
• Scratch and brown coat
• Veneer plaster
• Clay plaster

Rationale: Masonry block walls typically require a scratch coat and

brown coat for adhesion and durability.

• What is the purpose of keying the scratch coat?
• To prevent cracking
• To smooth the wall
• / 3