AR GP Gypsum & Plaster Contractor
Exam Questions and Correct Answers
(Verified Answers) Plus Rationale 2027
Q&A| Instant Download Pdf
Section 1: Gypsum and Plaster Materials
1. What is the primary ingredient in conventional gypsum plaster?
A. Portland cement
B. Hydrated lime
C. Calcium sulfate hemihydrate
D. Silica sand
Rationale: Calcium sulfate hemihydrate is the principal ingredient in
gypsum plaster. When mixed with water, it rehydrates to form calcium
,sulfate dihydrate, creating a hardened crystalline structure. This process
allows gypsum plaster to set without relying on cement hydration.
2. What happens chemically when gypsum plaster sets?
A. The plaster undergoes carbonation.
B. Calcium sulfate hemihydrate reacts with water to form calcium
sulfate dihydrate.
C. The plaster absorbs carbon dioxide to form calcium carbonate.
D. The plaster undergoes polymerization.
Rationale: Gypsum plaster sets through a hydration reaction in which
calcium sulfate hemihydrate combines with water and forms calcium
sulfate dihydrate crystals. These crystals interlock and provide strength.
This chemical reaction is distinct from the carbonation process
associated with traditional lime plaster.
3. Which material is commonly added to gypsum plaster to improve
workability and control setting characteristics?
A. Coarse gravel
B. Retarders and other formulation additives
C. Roofing tar
D. Reinforcing steel
,Rationale: Gypsum plaster formulations may contain retarders,
plasticizers, air-entraining agents, and other additives. Retarders slow
the setting reaction, providing additional working time. The appropriate
additive depends on the product formulation and the manufacturer's
instructions.
4. What is the primary purpose of using clean water when mixing
gypsum plaster?
A. To increase the plaster's weight
B. To prevent all shrinkage
C. To eliminate the need for curing
D. To avoid contamination that could interfere with setting and finish
quality
Rationale: Clean mixing water helps maintain predictable setting
behavior and plaster quality. Contaminants, including residues from
previously set plaster, may alter setting times or produce inconsistent
results. Clean water also reduces the risk of staining and other surface
defects.
5. Which condition generally causes gypsum plaster to set more
rapidly?
A. Using contaminated tools only
, B. Increasing the amount of clean water without limit
C. Using warmer mixing water within the product's permitted
temperature range
D. Applying plaster over a frozen substrate
Rationale: Warmer water can accelerate the hydration and setting
reaction of gypsum plaster. The actual effect depends on the product
formulation and temperature. Excessive heat or temperatures outside
the manufacturer's permitted range can cause application problems, so
specified mixing conditions must be followed.
6. What is the main purpose of a plaster bonding agent?
A. To waterproof every plastered surface
B. To replace the plaster itself
C. To eliminate the need for surface preparation
D. To improve adhesion between plaster and a suitable substrate
Rationale: Bonding agents help plaster adhere to surfaces that may
otherwise provide insufficient mechanical or chemical bonding. They are
commonly used on suitable smooth or dense substrates. The selected
agent must be compatible with the plaster and applied according to the
manufacturer's instructions.
Exam Questions and Correct Answers
(Verified Answers) Plus Rationale 2027
Q&A| Instant Download Pdf
Section 1: Gypsum and Plaster Materials
1. What is the primary ingredient in conventional gypsum plaster?
A. Portland cement
B. Hydrated lime
C. Calcium sulfate hemihydrate
D. Silica sand
Rationale: Calcium sulfate hemihydrate is the principal ingredient in
gypsum plaster. When mixed with water, it rehydrates to form calcium
,sulfate dihydrate, creating a hardened crystalline structure. This process
allows gypsum plaster to set without relying on cement hydration.
2. What happens chemically when gypsum plaster sets?
A. The plaster undergoes carbonation.
B. Calcium sulfate hemihydrate reacts with water to form calcium
sulfate dihydrate.
C. The plaster absorbs carbon dioxide to form calcium carbonate.
D. The plaster undergoes polymerization.
Rationale: Gypsum plaster sets through a hydration reaction in which
calcium sulfate hemihydrate combines with water and forms calcium
sulfate dihydrate crystals. These crystals interlock and provide strength.
This chemical reaction is distinct from the carbonation process
associated with traditional lime plaster.
3. Which material is commonly added to gypsum plaster to improve
workability and control setting characteristics?
A. Coarse gravel
B. Retarders and other formulation additives
C. Roofing tar
D. Reinforcing steel
,Rationale: Gypsum plaster formulations may contain retarders,
plasticizers, air-entraining agents, and other additives. Retarders slow
the setting reaction, providing additional working time. The appropriate
additive depends on the product formulation and the manufacturer's
instructions.
4. What is the primary purpose of using clean water when mixing
gypsum plaster?
A. To increase the plaster's weight
B. To prevent all shrinkage
C. To eliminate the need for curing
D. To avoid contamination that could interfere with setting and finish
quality
Rationale: Clean mixing water helps maintain predictable setting
behavior and plaster quality. Contaminants, including residues from
previously set plaster, may alter setting times or produce inconsistent
results. Clean water also reduces the risk of staining and other surface
defects.
5. Which condition generally causes gypsum plaster to set more
rapidly?
A. Using contaminated tools only
, B. Increasing the amount of clean water without limit
C. Using warmer mixing water within the product's permitted
temperature range
D. Applying plaster over a frozen substrate
Rationale: Warmer water can accelerate the hydration and setting
reaction of gypsum plaster. The actual effect depends on the product
formulation and temperature. Excessive heat or temperatures outside
the manufacturer's permitted range can cause application problems, so
specified mixing conditions must be followed.
6. What is the main purpose of a plaster bonding agent?
A. To waterproof every plastered surface
B. To replace the plaster itself
C. To eliminate the need for surface preparation
D. To improve adhesion between plaster and a suitable substrate
Rationale: Bonding agents help plaster adhere to surfaces that may
otherwise provide insufficient mechanical or chemical bonding. They are
commonly used on suitable smooth or dense substrates. The selected
agent must be compatible with the plaster and applied according to the
manufacturer's instructions.
