Lathing and Plastering (C-35) · Lesson 1 of 6

Minimum Plaster Thickness by Base and the Cubic-Foot Takeoff

"Minimum Plaster Thickness by Base and the Cubic-Foot Takeoff" is lesson 1 of 6 in the Lathing and Plastering (C-35) Learning Hub. It opens with "Thickness Is Set by the Code, Not by the Crew" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Thickness Is Set by the Code, Not by the Crew
  2. Read the Row for Your Base
  3. Know Where the Footnotes Change the Number
  4. Turn Thickness Into Cubic Feet
  5. Check the Wall After the Second Coat

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Find the exterior area" through "Apply footnote a to the ceiling".

What you'll be able to do

  • Explain the main idea of "Minimum Plaster Thickness by Base and the Cubic-Foot Takeoff" in plain language you can use on the exam.
  • Apply this step with confidence: "Know Where the Footnotes Change the Number".
  • Apply this step with confidence: "Turn Thickness Into Cubic Feet".
  • Apply this step with confidence: "Check the Wall After the Second Coat".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Plaster Thickness: Measured From the Face of the LathWALL SECTION, PLAN VIEW (exterior at right)face of lathstudcementplaster7/8 in minimumTABLE R702.1(1): MIN. PLASTER THICKNESSBASEGYPSUMCEMENTExpanded metal lath5/85/8Wire lath5/83/4 int / 7/8 extGypsum lath1/23/4 intMasonry walls1/21/2Footnote a: measured from the back plane ofexpanded metal lath (ribs excluded) orself-furring lath: 3/4 in minimumConcrete: max 5/8 gypsum, 7/8 cement (walls)TAKEOFF AT CODE MINIMUM (cubic feet = sq ft x thickness in / 12)Exterior wall 40 ft x 9 ft = 360 sq ft, wire lath: 360 x (7/8 / 12) = 26.25 cu ft = 0.97 cu ydCeiling 600 sq ft, gypsum on expanded metal lath: 600 x (5/8 / 12) = 31.25 cu ft = 1.16 cu ydSame ceiling if measured from back plane of lath (fn a): 600 x (3/4 / 12) = 37.5 cu ft = 1.39 cu ydMinimum finished thickness only; add waste and lath fill yourself (not a code number)Source: 2025 CRC Table R702.1(1) and footnote a; 2025 CBC §2511.3, §719.1CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Thickness Is Set by the Code, Not by the Crew

Plaster is ordered and inspected by finished thickness, and the California codes print the minimum for each kind of base. The 2025 California Residential Code Table R702.1(1) is titled "Thickness of Plaster" and gives the "finished thickness of plaster from face of lath, masonry, concrete" in inches, one column for gypsum plaster and one for cement plaster. Where grounds are installed, the 2025 California Building Code (CBC) section 2511.3 says they must ensure the minimum thickness and that thickness is measured from the face of lath and other bases.

Step 2: Read the Row for Your Base

Find the base in the left column, then read across. Expanded metal lath: 5/8 inch minimum for gypsum and 5/8 inch minimum for cement. Wire lath: 5/8 inch for gypsum, and for cement 3/4 inch minimum interior or 7/8 inch minimum exterior. Gypsum lath: 1/2 inch for gypsum plaster, 3/4 inch minimum interior for cement plaster. Masonry walls: 1/2 inch minimum for both. The exterior-over-wire-lath figure, 7/8 inch, is the one most exterior stucco takeoffs start from.

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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