Lathing and Plastering (C-35) · Lesson 4 of 6

Exterior Stucco: Lath Fastening and Weep Screed Layout

"Exterior Stucco: Lath Fastening and Weep Screed Layout" is lesson 4 of 6 in the Lathing and Plastering (C-35) Learning Hub. It opens with "Lath Must Be Corrosion-Resistant and Rigidly Backed" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Lath Must Be Corrosion-Resistant and Rigidly Backed
  2. Fastener Type and Spacing on Wood Framing
  3. Furring Rules
  4. Weep Screed: Material, Height and Overlap
  5. Water-Resistive Barrier Behind the Plaster

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Nail spacing along each stud" through "Weep screed level".

What you'll be able to do

  • Explain the main idea of "Exterior Stucco: Lath Fastening and Weep Screed Layout" in plain language you can use on the exam.
  • Apply this step with confidence: "Furring Rules".
  • Apply this step with confidence: "Weep Screed: Material, Height and Overlap".
  • Apply this step with confidence: "Water-Resistive Barrier Behind the Plaster".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Exterior Stucco: Lath Fastening and Weep ScreedSECTION AT BOTTOM OF WALL (not to scale)foundationstudearth4 in minabove earthfoundation plate linelath + plaster endon screed flangeweep screedLATH FASTENING (CRC R703.7.1)1 1/2 in long, 11-ga nails, 7/16 in head,or 7/8 in long, 16-ga staplesMax 7 in o.c. along studs or furringMax 24 in o.c. between framing or furringWEEP SCREED (CRC R703.7.2.1, CBC 2512.1.2)No. 26 gage (0.019 in) min; flange 3 1/2 in minAt or below the foundation plate lineMin 4 in above earth, 2 in above paved areasWater-resistive barrier laps the flangeLevel check (plate line = 100.00 ft)earth side: 99.00 + 4 in = 99.33 ftpaved side: 99.75 + 2 in = 99.92 ftScreed level: 99.92 to 100.00 ftMINIMUM NAIL COUNT: 8 ft STUDS, 24 ft WALL, STUDS 16 in o.c.Per stud: 96 in / 7 in = 13.7, round up to 14 spaces = 15 nails (both ends nailed)Studs: 24 ft x 12 / 16 = 18 spaces + 1 = 19 studs (16 in gaps are under the 24 in limit)19 studs x 15 nails = 285 nails minimum (staples at the same spacing)Source: 2025 CRC R703.7.1, R703.7.2.1; 2025 CBC §2512.1.2 (same weep screed numbers)CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Lath Must Be Corrosion-Resistant and Rigidly Backed

The 2025 California Building Code (CBC) 2510.4 says metal lath and lath attachments shall be of corrosion-resistant material, and 2510.5 says the backing or lath shall provide enough rigidity to permit plaster application. Where lath on a vertical surface runs between rafters or similar projecting members, CBC 2510.5.1 requires solid backing for the lath and its attachments. Wire backing is not required under expanded metal lath or paperbacked wire fabric lath (2510.5.3). Gypsum lath or gypsum wallboard is not allowed as the backing for cement plaster (2510.5.2.1), with an exception for self-furred metal lath or wire fabric lath over a water-resistive barrier on ceilings, roof soffits and interior walls.

Step 2: Fastener Type and Spacing on Wood Framing

The 2025 California Residential Code (CRC) R703.7.1 says lath is attached with 1 1/2-inch-long, 0.120-inch-diameter, 11-gage nails having a 7/16-inch head, or 7/8-inch-long, 16-gage staples. They are spaced not more than 7 inches on center along framing members or furring, and not more than 24 inches on center between framing members or furring, or as otherwise approved. Additional fastening between wood framing members is not prohibited. Where exterior plaster serves as wall bracing under Table R602.10.4, the lath is attached directly to framing. Lath attachment to cold-formed steel framing or to masonry, stone or concrete follows ASTM C1063.

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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