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Expanded mesh metal lath for plaster walls and ceilings © Daniel Friedman Expanded Metal Lath Systems
Interior Plaster & Exterior Stucco

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Installing plaster on expanded metal lath:

This article provides a photo guide to identifying and installing types of plaster support systems: metal lath, wire lath, etc. that are installed in buildings. We use building ceilings and walls as a photo and investigation guide to plaster and mortar lath systems.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

In this article series we describe and discuss the identification and history of older interior building surface materials such plaster, plaster board, split wood lath, sawn lath, and expanded metal lath, Beaverboard, and Drywall - materials that were used to form the (usually) non-structural surface of building interior ceilings and walls.

Expanded Mesh Metal Lath for Plaster Walls & Ceilings

Plaster lath board © Daniel FriedmanExpanded metal lath has been widely used to support both interior plaster in buildings and exterior building wall stucco systems.

This article explains plaster systems based on metal lath in building interiors.

Also see STUCCO WALL METHODS & INSTALLATION for a discussion of exterior uses of stucco and metal lath.

[Click to enlarge any image]

Plaster of the same general formula as discussed in the two wood lath based installations above was later applied over expanded metal lath.

Our photo shows expanded mesh metal lath used as plaster lath support for ceilings and walls; this material was also used on building exterior walls to support a stucco finish.

Metal lath was on occasion used also to support poured concrete ceilings (shown here) - unlikely to provide adequate strength for a thick pour unless additional reinforcement was used.

Depending on building age we may find a mixture of multiple types of plaster support, wood lath, gypsum board lath, and metal lath.

Wall or ceiling or stucco crack patterns may follow the borders of metal lath segments, especially if the lath was not securely nailed.

Van Den Branden and Hartsell explain that metal lath for plaster systems is divided into four groups with different properties for different applications:

Diamond mesh lath stacked for sale (C) Daniel Friedman InspectApedia.com

Photo above: diamond pattern expanded metal lath stacked for sale at a building supply store.

  1. Expanded metal lath - diamond mesh plaster lath, formed from sheet metal cut into a diamond pattern, pulled to an expanded shape.

Wire mesh lath used as a plaster base (C) Daniel Friedman InspectApedia.com

Photo above: expanded rib lath with stiffening ribs.

Modern diamond mesh lath is sold in a variety of metals including galvanized, stainless steel, finished to ASTM 653, and in a remarkable range of pre-formed shapes including

  1. Expanded rib lath - similar to diamond mesh but with stiffening ribs added

    Rib lath is used for installation of stone and tile on walls or plaster on interior ceilings. Heavier gauges of rib lath permit installation over spans of 19" o.c. instead of the stndard 16" o.c.

    Rib lath is sold currently as 1/8" flat rib lath and 3/8 High-Rib Lath used for ceilings and soffits and conforming to ASTM C1063.
  2. Wire lath (woven wire or welded wire - aka "chicken wire")

Perforated sheet lath used as a base for exterior stucco (C) Daniel Friedman at InspectApedia.com

Photo above: perforated sheet lath

  1. Sheet lath (popular early in the history of use of metal lathing, with a resurgence of use when shot or gun-applied plaster or cement mortars became widespread, often in commercial projects)
  2. Spray Lath:

    Spray Lath is used primarily on the West coast [of the U.S.], where stucco is spray applied to the surface of the lath to build stucco thickness.

    The Kraft paper is factory applied to prevent over spray of stucco. The spaces between the strips of Kraft paper allow for the visual alignment of the sheet for mechanical attachment of the ribs to the substrate.

    Rib Lath is often attached directly to the vertical framing members without a solid board substrate included.
    (AMICO 2019 cited below)

Properties of Diamond Mesh Metal Lath

Illustrated by our photo: diamond mesh metal lath from the wall cavity side, in a bathroom plumbing access wall cutout, provided by an InspectApedia.com reader.

A reader asked if the material shown in the plumbing access cutout photo here was asbestos. Our OPINON was that there is not likely to be a measurable asbestos hazard from this cement or plaster material, even if it contains asbestos, as long as it's left un-disturbed.

See details at ASBESTOS in PLASTER

Properties of Metal Rib Lath

Properties of Wire Mesh Lath

Properties of Sheet Lath - Perforated Sheet Metal Lath

Perforated sheet lath used as a base for exterior stucco (C) Daniel Friedman at InspectApedia.com

The photographs of sheet metal lath shown above and below illustrate perforated sheet metal lath that was used as a base for exterior stucco on a Poughkeepsie New York home inspected by the author.

Perforated sheet lath used as a base for exterior stucco (C) Daniel Friedman at InspectApedia.comAs you can see in these photographs, once water gets behind exterior stucco, especially in a northern climate subject to freezing temperatures, the action of water and frost break the mechanical bond that held the stucco cement to the metal lath.

Stages in the deterioration of a leaky stucco wall proceed roughly in this order

  1. Loose stucco, still in place, but not firmly bonded to the wall. Often you can push the stucco in and it moves, or you can tap on it and it sounds more-hollow than surrounding secure stucco wall sections.
  2. Stains and water damage appear on the outer surface of the stucco, and spalling of the surface or paint loss begin if the stucco was painted.
  3. The stucco bulges out from the wall
  4. Sections of stucco fall away from the wall, increasing the rate of water penetration and accelerating the damage to the stucco surfaces.

Watch out: when you see any of these stucco damage signs there is a good chance of more-serious hidden damage in the wall or ceiling cavity such as rot, insect attack, or mold contamination.

Further investigation is in order.

Below, from a commercial building, we see collapsing ceiling plaster below an area of roof leaks.

Plaster on metal lath ceiling collapse due to roof leaks (C) InspectApedia.com

Exterior Stucco Applications using Metal Lath

Trim leaks and trim rot admitting water into the stucco on metal lath exterior of a Poughkeepsie home (C) Daniel Friedman at InspectApedia.com

An example of the cause of leaks behind and extensive damage to the stucco on metal lath covered home shown above is the extreme degree of water leakage and rotted trim shown in our photograph of a Poughkeepsie NY home.

Lack of maintenance of the building trim led to extensive wall leaks and costly damage to the building stucco, trim, and windows.

Van Den Branden and Hartsell continue to point out that metal lathing for exterior stucco is similar to interior installations, with these changes:

Perforated sheet lath used as a base for exterior stucco (C) Daniel Friedman at InspectApedia.com

Watch out: do not use interior-grade metal lath for exterior wall stucco applications.

Metal lath is supplied in most markets in hot dipped galvanized (G 60) for exterior applications, and in painted or some equivalent rust-inhibitive coating, such as electrogalvanizing, for interior applications.

I have included this element because some contractors have installed painted or electrogalvanized lath for exterior applications.

According to ASTM C 1063, only G-60 hot dipped galvanized lath is allowed to be used for exterior applications. (Maylon 1996) 

More photographs of plaster walls & ceilings built on metal lath:

Our ceiling cavity photograph of a plaster on metal lath system (below left) shows how plaster applied to metal lath has considerably more adhesion security than plaster applied over wood lath.

Below (a New York garage ceiling) the plaster coating was left quite thin; you can see rusting metal lath around the light fixture and at the upper right in our photograph.

Plaster lath board © Daniel Friedman

See LOOSE PLASTER is UNSAFE for an example of a collapse of an expanded wire lath ceiling that had been improperly installed.

Loose Plaster is Unsafe, Especially Loose, Falling Plaster Ceilings

Watch out: for loose plaster that can fall and injure building occupants.

If ceiling plaster is bulged and moves when you apply gentle pressure to it, chances are that the plaster keys, the protruding plaster that oozed between the plaster lath strips to mechanically secure the plaster surface in place, have broken off.

Expanded Metal Lath Plaster Ceiling Catastrophic Collapse Case

Plaster lath board © Daniel Friedman

As we discuss in detail at at PLASTER, LOOSE FALL HAZARDS, plaster ceilings in newer buildings are not immune from collapse either, as you'll see by the catastrophic ceiling collapse shown just below.

This plaster ceiling was applied on expanded metal lath.

The lath was wired to steel pipes or bars that in turn were hung from a smaller number of steel supports.

The final steel supports were hung from wire ties connected to fasteners that had been "pin-shot fasteners" shot into the sides of concrete ceiling joists.

The combination of several factors led to this ceiling collapse:

See DRYWALL, FIBERBOARD, PLASTER INTERIORS where we include photographs of non-plaster interior wall and ceiling coverings including drywall, beaverboard, and paneling

Plaster lath board © Daniel Friedman

For plaster type surfaces used on building exteriors,

see STUCCO WALL METHODS & INSTALLATION.

Metal Lath Standards, Installation, History & Dates for Use as a Plaster Base

Star punched metal lath patent disclosure, Hayes 1890  (C) InspectApedia.comIn North America metal lath was in popular use before 1890, and the term "expanded metal lath", appearing in McCall's 1900 patent, was in popular use by 1914.

You'll see from the Hayes 1890 patent that early forms of metal lath were punched but were not using the "expanded metal lath" technique.

Metal lath patent 1984 Eckstein (C) InspectApedia.com

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Continue reading at PLASTER, LOOSE FALL HAZARDS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see PLASTER LATH, METAL FAQs - questions and answers about metal lath posted originally on this page.

Or see this

Article Series Contents

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PLASTER LATH, METAL at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING INTERIORS

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