Lath and Plaster Explained: What It Is and How to Price It

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.

SimplyWise Cost Estimator turns a photo of the wall into an itemized estimate in about 6 seconds.

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.

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 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.