# Lath and Plaster Explained: What It Is and How to Price It Canonical URL: https://www.simplywise.com/blog/lath-and-plaster/ Plain text: https://www.simplywise.com/blog/lath-and-plaster/llms.txt Publisher: SimplyWise, Inc. (https://www.simplywise.com) Published: September 21, 2026 Updated: October 5, 2026 Category: How to Estimate Summary: Lath and plaster explained: the historic wood lath wall, the modern ASTM C1063 and C926 assembly, the code coat counts, and the EPA lead rule. --- ## Lath and Plaster Explained: What It Is and How to Price It The old wall you just opened and the stucco wall you are bidding are both lath and plaster. At a glance 1. Lath is the base. Plaster is the wet material troweled over it in coats. 2. Cement plaster: C1063 for the lath, C926 for the plaster. Gypsum: C841 and C842. 3. The base sets the coat count: three over metal or wire lath, two over other bases the code permits. 4. Open plaster in a pre-1978 home and the EPA lead rule at 40 CFR 745 Subpart E applies. ## What is lath and plaster? Lath and plaster is a two part wall and ceiling assembly. The lath is a base fastened to the framing, made of narrow wood strips, expanded metal, wire fabric or gypsum board. The plaster is a wet gypsum or cementitious material troweled over that base in coats, squeezing through the openings and locking on as it sets. ## The historic wall you just opened The National Park Service documents the traditional assembly in Preservation Brief 21. Wood lath was nailed at right angles across the studs, and the plasterer pushed wet material through the gaps to form keys behind it. The coats had a fixed order. Scratch and brown were each about three eighths of an inch, the finish coat a mere one eighth. The material was lime plaster until gypsum took over near 1900. ## The standards behind modern lath and plaster ### ASTM C1063 covers the lath C1063 is the Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster. Fastener spacing, lap and furring live here. ### ASTM C926 covers the plaster C926 is the Standard Specification for Application of Portland Cement-Based Plaster. It covers full thickness plaster for exterior stucco and interior work, and holds the tables for mix proportions and thickness. ### Where the building code picks it up In the International Building Code, Chapter 25 covers plaster. Section 2507 is Lathing and Plastering, 2510 is Lathing and Furring for Cement Plaster, 2511 is Interior Plaster and 2512 is Exterior Plaster. Section 2510.3 says installation shall comply with ASTM C926 and C1063. The residential code puts interior plaster at R702.2 and exterior at R703.7.2. IBC 2511.1 puts interior plaster at not less than three coats over metal lath or wire fabric lath, and not less than two over other bases the chapter permits. Outside is not the same rule: IBC 2512.1 counts gypsum board backing into the three coat group and allows two only over masonry or concrete, while IRC R703.7.2 allows two over gypsum backing. Check which code your jurisdiction adopted. ## Lead and asbestos set your scope first The EPA Renovation, Repair and Painting rule sits at 40 CFR Part 745 Subpart E. Section 745.82 applies it to all renovations performed for compensation in target housing, meaning pre-1978 housing, and in child-occupied facilities. Section 745.83 exempts minor repair and maintenance, work disturbing six square feet or less of painted surface per room inside, or twenty outside. But that exemption is off the table if the work involves demolition of painted surface areas, so plaster removal is covered at any size. Work in the same room within thirty days counts as one job. Pre-1978 and for compensation means a certified renovator and the work practice standards at 745.85. Historic plaster can also contain asbestos. ## A worked example on one wall Take an interior wall twelve feet by eight feet, so 96 square feet. The base is metal lath over wood studs, so IBC 2511.1 puts you in three coat work. The occupation is Plasterers and Stucco Masons, SOC 47-2161. The May 2025 national median is $27.72 an hour, series OEUN000000000000047216108, against a $29.83 mean. Two plasterers spend six hours scratching and browning, then return three hours to finish. That is 18 worker hours. At the median, 18 times $27.72 is $498.96, or $5.20 a square foot in wage alone. The survey excludes the self employed, so treat it as a floor. ## Price the wall from a photo SimplyWise Cost Estimator turns a photo into an itemized estimate in about 6 seconds. Pricing is $29.99/mo or $239.99/yr, about $20/mo on annual, with a 7-day free trial. ## Where lath and plaster shows up on a job ### What the inspector looks at Lath attachment and lap first, because 2510.3 points straight at C1063. Then the water-resistive barrier under 2510.6 and the cure intervals in Table 2512.6. ### What it costs you to get wrong A missed lead determination on a pre-1978 house is federal enforcement exposure, not a punch item. Under 2510.5.2.1 gypsum lath is barred as a cement plaster backing outside, though the exception allows it on interior walls and ceiling soffits behind self-furred lath with a water-resistive barrier. ## Common mistakes on plaster scopes ### Merging two different materials Gypsum plaster and portland cement plaster answer to different standards. Gypsum takes ASTM C842 and C841, cement plaster C926 and C1063. ### Quoting a repair like drywall A plaster patch is a keyed, multi coat operation with cure time. Pricing it off a drywall installation cost (https://www.simplywise.com/blog/drywall-installation-cost/) number underbids the labor. ## Price a lath and plaster scope in four steps 1. Identify the base Wood, metal, wire fabric or rock lath. The base sets the coat count under IBC 2511.1. 2. Settle the year built Pre-1978 puts the job inside 40 CFR 745 Subpart E, and plaster demolition gets no six square foot pass. 3. Measure and count the coats Square footage times the coats the base requires, with cure intervals scheduled. 4. Build labor off a wage Start at the published median, then add burden, truck, material and margin. ## Keep reading - Construction Calculators (https://www.simplywise.com/blog/construction-calculators/) - Drywall Installation Cost (https://www.simplywise.com/blog/drywall-installation-cost/) - Painting Estimate Template (https://www.simplywise.com/blog/painting-estimate-template/) - Punch List (https://www.simplywise.com/blog/what-is-a-punch-list/) - SimplyWise Pricing (https://www.simplywise.com/blog/pricing/) ## Sources ### Standards - ASTM C1063-25 scope (https://store.astm.org/c1063-25.html) (2026-09-14). - ASTM C926-24 scope (https://store.astm.org/c0926-24.html) (2026-09-14). ### Code sections - IBC 2510, adopted text (https://up.codes/s/lathing-and-furring-for-cement-plaster-stucco) (2026-09-14). - IBC 2511 and IRC R702.2 (https://up.codes/s/interior-plaster) (2026-09-14). - IBC 2512, adopted text (https://up.codes/s/exterior-plaster) (2026-09-14). - IRC R703.7.2, adopted text (https://up.codes/s/plaster) (2026-09-14). ### Federal rule - 40 CFR 745 Subpart E, eCFR (https://www.ecfr.gov/current/title-40/chapter-I/subchapter-R/part-745/subpart-E) (2026-09-14). ### History and wages - NPS Preservation Brief 21 (https://www.nps.gov/orgs/1739/upload/preservation-brief-21-flat-plaster.pdf) (2026-09-14). - BLS OEWS 47-2161 (https://api.bls.gov/publicAPI/v2/timeseries/data/) (May 2025 national; 2026-09-14). ## Common questions about lath and plaster ### The assembly **What is lath and plaster?** Lath is a base fastened to the framing, made of wood strips, expanded metal, wire fabric or gypsum board. Plaster is the wet material troweled over it in coats, keying into the openings. **How many coats does plaster need?** The base decides. IBC 2511.1 requires not less than three coats over metal or wire fabric lath, and two over other permitted bases. ### Working on it **Is it safe to remove old plaster?** Not without checking the year built. In pre-1978 target housing, paid renovation falls under 40 CFR 745 Subpart E, and stripping plaster is demolition, so the six square foot exemption does not apply. **How old is lath and plaster construction?** Wood lath with lime plaster was standard until about 1900, when gypsum took over. Rock lath was almost universal in homes by the late 1930s. **What does a plasterer earn?** The May 2025 national median for Plasterers and Stucco Masons, SOC 47-2161, is $27.72 an hour against a mean of $29.83. --- ## About SimplyWise SimplyWise, Inc. (New York, NY) builds mobile apps for contractors, tradespeople, and small business owners. 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