InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
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
Expanded 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.
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)
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.
Produced by stamping or perforating a metal sheet, then expanding the holes by pulling its edges apart
Mesh size 5/16" x 9/16" diamond pattern - interior plastering, or larger mesh sizes for stucco work or as a support for loose fill rock wool or similar insulations
Self-furring: dimples into the surface hold the lath 1/4" away from the attaching surface, used for fireproofing structural columns
Paper-backed diamond mesh lath: waterproofed paper backing glued to the back to act as a moisture barrier and to reduce the amount of plaster consumed in applying the brown coat
2.5 or 3.4 pounds per square yard
Sheet size: 27" x 96", packed in 10 sheet bundles to cover 20 square yards
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.
Similar to Diamond Mesh Metal Lath above, with the addition of metal ribs formed lengthwise in the lath to add stiffness
Ribs are 1/8", 3/8" or 3/4" high.
Rib lath sheet sizes: 27" x 96" for 1/8", 3/8" ribs, 29" wide & 5', 10', & 12' lengths for 3/4" rib sizes
2.75, 3.4, & 4.0 pounds per square yard
A similar rib lath was produced by welding steel rods to the back surface of standard diamond mesh metal lath
Properties of Wire Mesh Lath
1" mesh: Constructed of galvanized woven wire (looks like "chicken wire") with 1" hexagonal openings, 20-gauge wire, sold in rolls, used over gypsum & fiber insulating lath board as reinforcement and for cornerite and stripite, used often as a stucco mesh over felt paper on open stud construction or over building sheathing
2" mesh: 16 gauge wire interwoven with fibrous absorbent paper backing secured by a 17 gauge wire corrugated every 4 3/8" to form a plaster key, in sheets 30 1/2 " x 49", in cartons of 44 sheets, 50 sq. yds., also used for stucco and open-stud construction.
Gun Lath: Welded wire lath, also referred to as "gun lath" suitable for machine applied (sprayed) mortars.
Properties of Sheet Lath - Perforated Sheet Metal Lath
Stiff metal sheet with perforations punched through the metal as slits, crosses, and ridges.
Self-furring design, mortar pushed through the slits forms necessary plaster ears or keys
4.5 lb /sq.yd.
27" x 96" sheets or 24" x 96" sheets
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.
As 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
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.
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.
The stucco bulges out from the wall
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.
Exterior Stucco Applications using Metal Lath
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:
Use of a covering of all exterior surfaces with a waterproof building paper or plastic,
Use of heavier gauge metal lath with larger mesh openings
Lath is not applied in direct contact with the background or base, by using furring nails that hold the lath out 1/4" to 3/8" from the base or framing
[this permits plaster to penetrate the lath and form securing keys]
Use of protective flashings and details to keep water from passing behind the lath (and stucco surface)
Use of control joints
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.
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
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:
Metal Lath Standards, Installation, History & Dates for Use as a Plaster Base
In 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.
Amico, METAL LATH and ACCESSORIES, [PDF] Alabama Metal Industries Corporation
3245 Fayette Avenue, Birmingham, AL 35208 USA Tel:(205) 787-2611 (800) 366-2642 Website: www.amico-lath.com Email: email@example.com Amico is a Gibraltar Industries company.
Amico has offices throughouth the U.S. and Canada as well as in the United Kingdom and Germany.
Clark Dietrich, BEST PRACTICES for SELECTION & INSTALLATION of EXPANDED METAL LATH PRODUCTS [PDF], (2014) ClarkDietrich™ Building Systems, 9050 Centre Pointe Drive, Suite 400
West Chester, OH 45069 USA, Tel:(513) 870-1100 Website: https://www.clarkdietrich.com, E-mail: firstname.lastname@example.org
retrieved 2019/01/12, original source: https://www.clarkdietrich.com/sites/default/files/imce/pdf/WhitePapers/2014_Jan_Lath/CD_WP_Expanded_Metal_Lath-Jan2014.pdf
ASTM C 842 - 05 (2015) Standard Specification for Application of Interior Gypsum Plaster, available from ASTM at https://www.astm.org/Standards/C842.htm
This specification covers the minimum requirements for full-thickness interior gypsum plastering on gypsum, metal, masonry, or monolithic concrete bases designed or prepared to receive gypsum plaster.
Gypsum plaster applied to the interior side of exterior walls of masonry or concrete shall be isolated from the exterior wall. Gypsum plasters shall not be used in exterior locations or interior wet areas.
Plasters and other cementitious materials shall be kept dry until used; they shall be stored off the ground, under cover, and away from walls with condensation and other damp surfaces.
Metal products shall be protected, while stored, against rusting.
The surface preparations of plasters are presented in details. All plaster mixing shall be done by mechanical means unless hand mixing is specified. Plaster shall be applied by hand or machine as specified.
ASTM C 841 - 03 (2013) Standard Specification for Installation of Interior Lathing and Furring, available from ASTM at https://www.astm.org/Standards/C841.htm Abstract:
This specification covers the minimum requirements for, and the methods of application of, interior lathing and furring to receive gypsum plaster applied. Other materials are not prohibited from being used provided that their physical characteristics and durability under conditions of usage are at least equal in performance to those described.
All materials shall be kept dry, preferably by being stored inside.
Where necessary to be stored outside, materials shall be stacked off the ground, supported on a level platform, and protected from the weather and surface contamination. Materials shall be neatly stacked flat with care taken to avoid damage to edges, ends, or surfaces.
The materials to be used are the following: tie wire and hanger wire, gypsum lath, expanded metal lath, welded wire lath, woven wire lath, nails, screws, staples, paper, and accessories such as control joints, cornerite, channels, rod and flat hangers, clips, and striplath.
In general, during installation, the following shall be required: application of gypsum lath to supports, application of gypsum lath to wood supports, application of gypsum lath to metal supports, studless solid partitions (gypsum lath and plaster), application of metal plaster bases to framing members, studless solid partitions (metal lath and plaster), suspended and furred ceilings (metal lath and gypsum lath construction), main runners, cross furring, and metal furring for walls.
EMLA, GUIDE SPECIFICATIONS for EXPANDED METAL LATHING and FURRING [PDF] 5th Ed., (2009) NAAM EMLA 920-09 Expanded Metal Lath Association, NAAMM Headquarters 800 Roosevelt Rd. Bldg. C, Suite 312 Glen Ellyn, IL 60137 USA (630) 942-6591 phone email@example.com Website: NAAMM EMLA https://www.naamm.org/division/3
Retrieved 2019/01/12 original source https://www.naamm.org/content/uploads/products/emla_920-09.pdf
The Expand Metal Lath Association (EMLA) of the National Association of Architectural Metals Manufacturers (NAAMM) has run a comprehensive testing program to determine the minimum acceptable load for expanded metal lath for transverse loading with a traditional 3-coat stucco wall system.
The third party test results proved these types of wall systems perform exceptionally well in high-wind zone environments. The stucco tests were performed in August, 2011 at Smith-Emery Laboratories in Los Angeles, CA, following the ICC’s – Acceptance Criteria (AC) 191 – Acceptance Criteria for Metal Plaster Bases (Lath) – using Code-Compliant Lath & fasteners, studs, weather-barrier and sheathings.
The test frames were constructed in accordance with AC191 and the lath plaster were installed according to ASTM C-1063 – Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster and ASTM C-926 Standard Specification for Application of Portland Cement-Based Plaster.
LATH & PLASTER SYSTEMS, 092300/NGC, [PDF] National Gypsum Lath and Plaster Systems, National Gypsum Corporation, 800-628-4662 describing National Gypsum's Kal-Kore brand plaster base
Gypsum Construction Guide, National Gypsum Corporation
Home Depot Stores, HOW to INSTALL METAL LATH [PDF], retrieved 2019/01/12, original source: Home Depot Stores, https://images.homedepot-static.com/catalog/pdfImages/0a/0afff321-4174-47da-96bc-768e2f52d66d.pdf
Minnesota Lath & Plaster Bureau, LATH INSPECTION RESOURCE MANUAL [PDF], 2nd. Ed., Minnesota Lath & Plaster Bureau, Minnesota Lath and Plaster Bureau
10600 University Avenue NW Suite 3 Coon Rapids, MN 55448 USA Tel: 763-757-MLPB (6572) Email: firstname.lastname@example.org
retrieved 2019/01/12, original source: http://www.mnlath-plaster.com/library/documents/LathInspectionResourceManualUpdate2009.pdf
Website excerpt: The Minnesota Lath and Plaster Bureau has promoted the industry since 1953. It is
widely recognized as an education and technical spokesman for the industry. It provides services to architects, the construction community and the public on a variety of matters relating to the plastering trades.
Effective 1-1-19 the office operations of the Minnesota Lath and Plaster Bureau were suspended.
Hayes G., "Metallic Lathing", U.S. Patent 420656, issued February 4, 1890
Excerpt: ... have invented a new and useful Metallic Lathing, of which the following is a specification.
My invention consists of a lathing of sheet metal having at intervals throughout tongued apertures of polygonal shape, the perimeter of each opening having more than four sides and with all its angles obtuse, the aperture made by cutting incisions and turning out ward the edge metal of the cuts outward until the proper size and shape of the opening are obtained.
The edge metal so turned outward is left projecting beyond the plane of one side of the sheet as tongues, hooks, or barbs to grasp plaster when applied thereto, all as hereinafter more fully specified, reference being had to the accompanying drawings, in which-
Figure 1 is a face view of a piece of the sheet-metal lathing, showing the tongued apertures of pentagonal shape arranged in direct lines. Fig. 2 is a face view of a piece of the lathing with pentagonal aperture arranged in diagonal line across the sheet.
Fig. 3 is a face view of a piece of the lathing having tongued apertures of hexagonal shape arranged in diagonal lines across the sheet.
Fig. i is a face view of a piece of the lathing having hexagonal apertures arranged in direct lines. Fig. 5 is a face View of a piece of the lathing with apertures of elongated hexagonal shape arranged in diagonal lines across the sheet.
... A sheet-metal lath having at intervals throughout apertures of polygonal shape whose perimeter consists of more than four sides and of which all angles are obtuse,
each aperture formed by cutting incisions radiating from centers and turning outward with a backward bend or roll, the pointed edge metal from between the cuts to stand at the verge of the aperturaprojecting beyond the plane of the sheet as tongues, hooks, or barbs to grasp plaster when applied thereto, as herein set forth.
Curtis, O.H., "Metal Lathing", U.S. Patent 460,850, issued 10 October 6, 1891
Excerpt:... have invented a new and useful Improvement in Metal Lathing, of which the following is a full, clear, and exact description.
This invention relates to that description of metal lathing which is constructed of sheet metal having cuts made in it forming openings for entry and clinching of the plaster and in which the cut portions remain attached and are bent to protrude beyond the surface of the sheet, which is made corrugated in addition, to give strength.
The object of my invention is to produce a simple, easily manufactured, and improved fire and vermin proof metal lath of this description, substantially as hereinafter described,and more particularly pointed out in the claims.
Ohl, G.A., "Machine for Making Metal Lathing", U.S. Patent 475,700 Issued 24 May 1892
Excerpt: ... have invented certain new and useful Improvements in Lath- Machines, fully described and representedin the following specification and the accompanying drawings, forming a part of the same.
The apparatus herein described is adapted to to form slots in a sheet of thin metal, with strips attached at both ends to the sheet behind the slot to form a metallic lath to retain plaster upon walls; and the improvement c011- sists in the particular construction of the rolls and strippers hereinafter described.
Eckstein, William, "Metallic Lathing", U.S. Patent 514313, issued 6 Februray 1894 previously patented in Great Britain in 1892.
Excerpt: Be it known that I, WIILLIAM ECKSTEIN, of 187 Union Street, London, S. E., in the county of Surrey, England, have invented a new and useful Improvement in Metallic Lathing, (for which I have obtained Letters Patent in Great Britain, No. 11,036, dated June 11, 1892,) of which the following is a full, clear, and exact description.
The invention relates to metallic lathing having means such as keys, loops, or spurs,
for causing the plaster when applied thereto, to be interlocked with such lathing.
Various forms of plaster-engaging devices have been provided, and the present invention has for its object to improve and make more efficient such plaster engaging devices, and at the same time greatly increase the rigidity of the plate.
Mccall, William. "Metal-lath attachment and support." U.S. Patent 657,827, issued September 11, 1900.
Excerpt: The objects of my invention are to provide a means for rapidly attaching the sections of wire or expanded metal laths to the partitions, ceiling, or other portions where the lath and plastered surfaces are to be applied
Chester, Frank Stanley. "Metal lath." U.S. Patent 764,989, issued July 12, 1904.
Excerpt: ... a new and improved metal lathwhich can be economically manufactured and which will hold plaster securely in position on the surface of the lath and one which will economize in the quantity of plaster to be used.
Alschuler, Alfred S. "Metal-lath construction." U.S. Patent 802,727, issued October 24, 1905.
Scammell, Charles H. "Expanded metal lath." U.S. Patent 1,087,511, issued February 17, 1914.
Excerpt: ... new and useful Improvements in Expanded Metal Lath, fully described and represented in'the following specification and the accompanying drawings, forming a part of the same.
This invention relates ,to expanded "metal lath of that class formed by slitting the metal. and drawing out the strands to open the slits and turn the strands at an angle to the plane of the metal and which is used generally as lathing to hold plaster in building construction, althi'iugh applicable, also to other uses.
Scammell, Charles H. "Metal lath." U.S. Patent 1,210,849, issued January 2, 1917.
Dickinson, Clarence W. "Expanded-metal lath." U.S. Patent 1,372,741, issued March 29, 1921.
Sagendorph, Robert H. "Metal lath." U.S. Patent 1,701,125, issued February 5, 1929. Assigned to Eastern Expanded Metal Co.
Patent excerpt: This invention relates to metal lath, an object of the invention being to provide an improved lath formed by first slitting and then expanding a met-al sheet, and thereafter applying a coating material to the face of the slitted
and expanded sheeting such manner as to cover predetermined portions of the sheet so as to provide keyways or spaces of, considerable less total area than the area of the sheet for retaining the plaster when applied, thereby enablin a very considerable saving in the amount of plaster used.
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.
American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, www.apawood.org
Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on ASBESTOS, ITS INDUSTRIAL APPLICATIONS, ROSATO 1959, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print).
ASHI, American Society of Home Inspectors,® Inc., 932 Lee Street, Suite 101, Des Plaines, Illinois, 60016. The American Society of Home Inspectors is the first and leading national association of home inspectors in the U.S. Website: www.ashi.org
ASTM C 842
ASTM C 841 Metal Lath or gypsum lath installation
Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
How could homes be designed and built more efficiently?
What kinds of construction and production techniques worked well and which did not?
How did people use different kinds of spaces in their homes?
What roles did community planning, zoning, and interior design play in how neighborhoods worked?
Isham: "An Example of Colonial Paneling", Norman Morrison Isham, The Metropolitan Museum of Art Bulletin, Vol. 6, No. 5 (May, 1911), pp. 112-116, available by JSTOR.
Plastering, PM 5, Product & Systems Technology, US Gypsum, May 1998, web search 10.5.2010, original source: http://www.usg.com/rc/technical-articles/plaster/
United States Gypsum Company, 125 South Franklin ST., PO Box 806278, Chicago, IL 60680-4124,
Paraphrasing from this document: USG uses the term shadowing in this document in describing the visual effect over gypsum board joints caused by the lower moisture absorption rate (take-up) and lower capacity than gypsum base face paper. Shadowing at joints occurs where veneer plaster is applied over tape joints, requiring a second coat to completely hide the tape, providing a visually uniform surface. USG Advises: "This [second] cover coat must be allowed to harden and dry before plaster application is started.
Construction Handbook [purchase at Amazon.com] H17, Technical
Folder SA920 and PM2, PM3 and PM4, United States Gypsum Company, 125 South Franklin ST., PO Box 806278, Chicago, IL 60680-4124,
Plastering Skills, F. Van Den Branden, Thomas L. Hartsell, Amer Technical Pub (July 1, 1985), ISBN-10: 0826906575, ISBN-13: 978-0826906571 [purchase at Amazon.com]
Gypsum Construction Guide, National Gypsum Corporation
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones