CO Plastering Contractor Exam
Questions And Correct Answers
(Verified Answers) Plus Rationale2026
Q&A| Instant Download Pdf
1. What is the primary purpose of plaster in construction?
A. Insulation
B. Decoration
C. Protection and surface finishing
D. Structural support
Rationale: Plaster is primarily used to protect walls and provide a
smooth surface for decoration, not as structural support.
2. Which type of plaster sets fastest?
A. Lime plaster
B. Gypsum plaster
C. Cement plaster
D. Clay plaster
Rationale: Gypsum plaster sets quickly due to its chemical reaction
with water, making it ideal for interior finishing.
3. What is the standard water-to-cement ratio for cement plaster?
A. 0.5
B. 0.6
C. 0.75
D. 1.0
Rationale: A water-to-cement ratio of 0.75 provides workability
without compromising strength.
4. Which aggregate is typically used in plaster?
A. Gravel
, B. Sand
C. Crushed stone
D. Pea gravel
Rationale: Sand provides a fine, workable texture for plaster and
ensures smooth application.
5. What is the recommended thickness for a single coat of cement plaster
on walls?
A. 3 mm
B. 5 mm
C. 10 mm
D. 20 mm
Rationale: A 10 mm coat is standard to ensure good adhesion and
durability.
6. What is “scratch coat” in plastering?
A. Final finishing layer
B. Protective primer
C. First rough coat to key subsequent layers
D. Decorative coat
Rationale: The scratch coat provides a rough surface that helps the
next plaster layer adhere.
7. What type of plaster is best suited for wet areas like bathrooms?
A. Lime plaster
B. Clay plaster
C. Cement plaster
D. Gypsum plaster
Rationale: Cement plaster is water-resistant and suitable for damp
areas.
8. Which tool is used to achieve a smooth plaster surface?
A. Hammer
B. Trowel
C. Float
D. Chisel
Rationale: A float is used to smooth plaster after it is applied.
9. How long should cement plaster cure before painting?
A. 1 day
B. 3 days
C. 7–14 days
, D. 1 month
Rationale: Proper curing allows the plaster to harden and avoid
cracking when painted.
10. What is the main disadvantage of gypsum plaster in wet areas?
A. Hardening time
B. Dissolves in water
C. Cost
D. Difficulty in application
Rationale: Gypsum plaster is not suitable for wet areas because it is
water-soluble.
11. Which additive can improve plaster workability?
A. Sand
B. Water
C. Plasticizer
D. Cement
Rationale: Plasticizers enhance workability without increasing water
content.
12. What is the main function of a bonding agent in plastering?
A. Add color
B. Improve adhesion to the substrate
C. Speed drying
D. Increase thickness
Rationale: Bonding agents help plaster adhere better to smooth or
non-porous surfaces.
13. What is the ideal temperature for plaster application?
A. Below 0°C
B. 10–30°C
C. 35–40°C
D. Above 45°C
Rationale: Plaster should be applied in moderate temperatures to
avoid rapid drying or freezing.
14. Which is a common defect in plastering?
A. Smooth surface
B. Cracking
C. Proper curing
D. Uniform thickness
Questions And Correct Answers
(Verified Answers) Plus Rationale2026
Q&A| Instant Download Pdf
1. What is the primary purpose of plaster in construction?
A. Insulation
B. Decoration
C. Protection and surface finishing
D. Structural support
Rationale: Plaster is primarily used to protect walls and provide a
smooth surface for decoration, not as structural support.
2. Which type of plaster sets fastest?
A. Lime plaster
B. Gypsum plaster
C. Cement plaster
D. Clay plaster
Rationale: Gypsum plaster sets quickly due to its chemical reaction
with water, making it ideal for interior finishing.
3. What is the standard water-to-cement ratio for cement plaster?
A. 0.5
B. 0.6
C. 0.75
D. 1.0
Rationale: A water-to-cement ratio of 0.75 provides workability
without compromising strength.
4. Which aggregate is typically used in plaster?
A. Gravel
, B. Sand
C. Crushed stone
D. Pea gravel
Rationale: Sand provides a fine, workable texture for plaster and
ensures smooth application.
5. What is the recommended thickness for a single coat of cement plaster
on walls?
A. 3 mm
B. 5 mm
C. 10 mm
D. 20 mm
Rationale: A 10 mm coat is standard to ensure good adhesion and
durability.
6. What is “scratch coat” in plastering?
A. Final finishing layer
B. Protective primer
C. First rough coat to key subsequent layers
D. Decorative coat
Rationale: The scratch coat provides a rough surface that helps the
next plaster layer adhere.
7. What type of plaster is best suited for wet areas like bathrooms?
A. Lime plaster
B. Clay plaster
C. Cement plaster
D. Gypsum plaster
Rationale: Cement plaster is water-resistant and suitable for damp
areas.
8. Which tool is used to achieve a smooth plaster surface?
A. Hammer
B. Trowel
C. Float
D. Chisel
Rationale: A float is used to smooth plaster after it is applied.
9. How long should cement plaster cure before painting?
A. 1 day
B. 3 days
C. 7–14 days
, D. 1 month
Rationale: Proper curing allows the plaster to harden and avoid
cracking when painted.
10. What is the main disadvantage of gypsum plaster in wet areas?
A. Hardening time
B. Dissolves in water
C. Cost
D. Difficulty in application
Rationale: Gypsum plaster is not suitable for wet areas because it is
water-soluble.
11. Which additive can improve plaster workability?
A. Sand
B. Water
C. Plasticizer
D. Cement
Rationale: Plasticizers enhance workability without increasing water
content.
12. What is the main function of a bonding agent in plastering?
A. Add color
B. Improve adhesion to the substrate
C. Speed drying
D. Increase thickness
Rationale: Bonding agents help plaster adhere better to smooth or
non-porous surfaces.
13. What is the ideal temperature for plaster application?
A. Below 0°C
B. 10–30°C
C. 35–40°C
D. Above 45°C
Rationale: Plaster should be applied in moderate temperatures to
avoid rapid drying or freezing.
14. Which is a common defect in plastering?
A. Smooth surface
B. Cracking
C. Proper curing
D. Uniform thickness
