Painting and Decorating (C-33) · Lesson 6 of 6

Film Build: Checking Each Coat and the Total Against the Spec

"Film Build: Checking Each Coat and the Total Against the Spec" is lesson 6 of 6 in the Painting and Decorating (C-33) Learning Hub. It opens with "Film Thickness Is Measured in Mils" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Film Thickness Is Measured in Mils
  2. A Water-Borne System Table
  3. Add the Ranges as a Check
  4. Other Coat Thicknesses the Specification Prints
  5. Pass or Fail

The worked example in the course applies this lesson to a realistic job in 6 steps, starting with "Corrective action".

What you'll be able to do

  • Explain the main idea of "Film Build: Checking Each Coat and the Total Against the Spec" in plain language you can use on the exam.
  • Apply this step with confidence: "Add the Ranges as a Check".
  • Apply this step with confidence: "Other Coat Thicknesses the Specification Prints".
  • Apply this step with confidence: "Pass or Fail".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Film Build: Each Coat and the TotalBARE METAL SYSTEM (§59-2.01C(4)(c))1st undercoat (145): 2-3 mils2nd undercoat (146): 2-3 mils1st finish (181): 1.5-3 mils2nd finish (182): 1.5-3 milsTotal, all coats: 7-12 milsOTHER LIMITS PRINTEDExisting painted: 146, 181, 182Total of new coats: 5-9 milsGalvanized (§59-3.03):each finish at least 2 milsall coats 4-8 milsITEM 1: BARE METAL2.4 + 2.8 + 1.6 + 1.2= 8.0 total (7-12 OK)2nd finish 1.2 isunder the 1.5 minimumFAILITEM 2: TOPCOAT ONLY2.5 + 1.5 + 1.5= 5.5 total (5-9 OK)Every coat is in rangePASSITEM 3: GALVANIZED1.8 + 2.5= 4.3 total (4-8 OK)1st finish 1.8 is underthe 2 mil minimumFAILCheck every coat AND the total: a good total can hide one thin coatSource: 2025 Caltrans Standard Specifications §59-2.01C(4)(c), §59-3.03CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Film Thickness Is Measured in Mils

Dry film thickness (DFT) is the thickness of the cured coating, measured in mils; 1 mil is 0.001 inch. The 2025 Caltrans Standard Specifications give DFT as a range for each coat and for the whole system, and a coating can fail on the total even when every coat is in range, or on one coat even when the total is fine. §59-1.01D says DFT is measured with a calibrated Type 2 magnetic film thickness gauge under SSPC-PA 2, except that the Engineer may ask for any number of additional spot measurements (the Specification refers to the SSPC procedure; it does not print it).

Step 2: A Water-Borne System Table

§59-2.01C(4)(c), State Specification Paint Waterborne Coating System for existing structural steel. Surfaces cleaned to bare metal (includes spot blast locations): 1st undercoat (State spec 145) 2-3 mils; 2nd undercoat (146) 2-3; 1st finish coat (181) 1.5-3; 2nd finish coat (182) 1.5-3; total thickness, all coats 7-12 mils. Existing painted surfaces to be topcoated: undercoat (146) 2-3; 1st finish (181) 1.5-3; 2nd finish (182) 1.5-3; total of the new coats 5-9 mils. Allow at least 12 hours of drying before the next coat unless otherwise authorized.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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