CSLB C-33 Painting & DecoratingCoating ApplicationMedium
A painting contractor is applying a two-part epoxy coating to a concrete floor in a commercial kitchen. The manufacturer's instructions state a mixing ratio of 4:1 by volume (Part A: Part B) and a pot life of 60 minutes at 75°F. The contractor has mixed 4 gallons of Part A. How much of Part B should be added, and what is the maximum time the mixed material should be used if the ambient temperature is 75°F?
- A1 gallon of Part B; 60 minutes working time.
- B1.25 gallons of Part B; 60 minutes working time.
- C1.25 gallons of Part B; 90 minutes working time.
- D1 gallon of Part B; 30 minutes working time.
Show answer & explanationAnswer & explanation
Correct answer: A. 1 gallon of Part B; 60 minutes working time.
For a 4:1 ratio (Part A: Part B) and 4 gallons of Part A, 1 gallon of Part B is required (4 gallons / 4 = 1 gallon). The pot life, which is the maximum working time, is explicitly stated as 60 minutes at 75°F. Therefore, the contractor has 60 minutes to use the mixed material.
Why the other options are wrong
- B. Incorrect calculation for Part B. 1.25 gallons would be a 3.2:1 ratio (4/1.25).
- C. Incorrect calculation for Part B and incorrect pot life. Pot life is 60 minutes, not 90.
- D. Incorrect pot life. The pot life is given as 60 minutes.
Two-Part Coating Mixing & Pot Life
Two-part (2K) coatings require precise mixing ratios of base and activator, and once combined, they have a limited 'pot life' (working time) due to chemical reactions.
- Mixing ratio is critical for proper curing and performance.
- Pot life is temperature-dependent; higher temperatures reduce working time.
- Exceeding pot life leads to gelation, poor adhesion, and coating failure.
Memory trick: Mix the parts right, then race the clock before it sets too tight.