CSLB C-39 Roofing ContractorLow-Slope RoofingHard
A technician is preparing to apply an elastomeric roof coating early in the morning on a humid day. Manufacturer specifications require the substrate temperature to remain at least 5°F above the dew point during application and curing. If the current dew point is 58°F, what is the minimum acceptable substrate temperature for coating application?
- A53°F
- B63°F
- C58°F
- D68°F
Show answer & explanationAnswer & explanation
Correct answer: B. 63°F
The substrate temperature must be at least 5°F above the dew point to prevent condensation from forming on or within the coating during cure. 58°F (dew point) + 5°F = 63°F minimum substrate temperature.
Why the other options are wrong
- A. This is 5°F below the dew point, the opposite of the required margin.
- C. This equals the dew point exactly, with no safety margin against condensation.
- D. This adds too large a margin (10°F) beyond the specified requirement.
Dew Point Coating Application Rule
Roof coatings must be applied when the substrate temperature is a specified margin (commonly 5°F) above the dew point to prevent condensation from compromising adhesion and cure.
- Condensation on a cold substrate can cause coating defects and poor adhesion
- Dew point rises with humidity and falls with temperature drop
- Early morning and humid conditions increase risk of dew point violations
Memory trick: Stay 5 degrees clear of the dew, or the coating goes askew.