Plaster Ceilings, Plaster Walls & Plaster Type Identification in buildings

Plaster & plaster lath ceiling types, history, age determination
- Plaster System identification and history of use
- Photo guide to split wood lath, pit-sawn lath, circular blade sawn wood lath, expanded metal lath, "rock lath" or plasterboard, drywall, & tainted Chinese drywall
- Photo guide to plaster coatings, cracks, hazards
- Plaster ceiling collapse hazards & photographs
Questions & Answers about how to identify different types of interior wall & ceiling plaster installation methods &
References

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Types of plaster walls & ceilings: here we provide a photo guide to identifying types of plaster ceilings and walls installed in buildings, using building ceilings as a photo and investigation guide. 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.

Guide to Plaster Ceiling & Wall Covering Systems in buildings

Photo Guide to Types Interior Plaster: split wood lath, sawn wood lath, expanded metal lath, "rock lath" or plasterboard, drywall, & tainted Chinese drywall

See Plaster & Beaverboard & Drywall where we include photographs of non-plaster interior wall and ceiling coverings including drywall, beaverboard, and paneling. Also see drywall identification photos at CHINESE DRYWALL HAZARDS. For plaster type surfaces used on building exteriors, see STUCCO WALL METHODS & INSTALLATION.

Plaster Ceilings & Walls Applied over Wood Lath

Hand Split Wood Lath Based Plaster Ceilings & Walls

Photograph of hand-split wood lath and plaster wall, from the wall-cavity side. Ca 1800. Hand split wood lath will vary in width as you see in our photo (left).

There are several generations of plaster and lath, plaster board, and drywall which have been used in buildings.

We name and illustrate these and discuss their periods of use below as an aid in finding out how old a building is and tracing its history. Examples:

Mud used as a plaster over split wood lath or woven wood lath

Horsehair mixed with plaster or cement for building exterior wall covering

Plaster of paris applied in at least two layers, a rough brown or scratch coat and a smooth white plaster top coat over hand split wood lath;

Sawn-Wood Lath Based Plaster Ceilings & Walls

Our photographs below show traditional sawn wood lath used as the supporting base for a typical three-coat plaster ceiling or wall system. As with the older split wood lath, plaster of paris was applied in at least two layers, usually three layers: a rough brown or scratch coat and a smooth white plaster top coat over sawn wood lath.

At left you can see the "ears" or "plaster ears" formed by the plaster base coat, or brown coat (the first plaster layer) applied onto the wood lath of this antique New York home.

You'll also notice that especially in older structures whose interior partition walls often used minimal and irregularly-spaced framing for interior walls and ceilings, the plasterer sometimes tacked up an extra wood scrap (the diagonal log in our photo at left) to improve support for plaster lath, or to provide a nailing surface to secure the ends of wood lath that otherwise did not reach a vertical wall stud.

Watch out: often the framing supporting plaster ceilings in homes built before 1900 was sized to be just strong enough to support the weight of the plaster itself. Such ceiling structures were not intended to support the weight of a curious home owner or home inspector.

Below (left) is a photo of an 1870's home in "the Bleachery" in Wappingers Falls, NY, restored by the author (DF). Most of the plaster ears had broken away and plaster was falling from the walls and ceilings in this home. Using a flat-bladed shovel we elected to remove all of the loose plaster.

Our second wood lath plaster photo (below right) is particularly interesting because at least one of the wood lath sections shows the vertical, but regularly-spaced saw kerf marks of a machine operated pits saw, a means of cutting wood used before circular saws were available and helping to date this building as pre 1840 in New York.

At left we show a mud-straw mix of plaster base coat used in a late 18th century New York home, ca 1785.

Plaster on Lath Coatings

Our plaster wall and ceiling photos below demonstrate the stages in constructing an traditional plaster on lath surface. Our photo at below left shows a common practice in roughly-finished attics: just a thin skim coat of plaster was applied directly to the wood lath - you can see the wood lath telegraphing through the plaster coating. Very often plaster cracking follows the lines of these lath strips.

Our plaster scratch coat or "brown coat" photo (below right) shows how this surface was sometimes scarified to provide better adhesion of the top coats of plaster. However often the brown coat was simply applied roughly without gouging, as we show in this extra plaster rough coat photo.

Gypsum Board Lath Sheets Used for Plaster Walls & Ceilings = Rock Lath, Plaster Lath, or Rock Lathe

Our photo (above left) shows perforated gypsum board panels that were used as plaster lath. Solid gypsum board (above right, without holes) was also used as a support for a plaster finish coat. Often this material was applied in two-foot widths - a feature that the inspector may spot by noticing scalloped ceilings and walls or even cracks that appear regularly on 24" centers.

Gypsum board lath: Plasterboard with round holes punched at regular intervals substituted for the plaster scratch coat, nailed to wall studs, eliminating the wood lath requirement. A top coat of plaster was applied to the plaster board. "Ears" of oozing plaster pushed through the round holes helped hold the plaster top coat in place

Our wall cross section cutaway photograph of gypsum board lath installed on a New York home (photo at left) shows how these walls are constructed, and you can see quite clearly the top coats of plaster that were applied over the gypsum board itself. [Click any image for an enlarged, detailed view.]

Here is another photograph of a plaster wall test cut that shows a closeup of the layers of plaster board and top coats that make up the wall surface in a 1930's-built home whose plaster-board lath included wood fiber reinforcing materials.

Contemporary gypsum lath products include GoldBond® brand gypsum board products including Kal-Kore brand plaster base panels sold by National Gypsum Corporation. Kal-Kore plaster base panels are designed as a base for veneer plaster, but these can also be used as basecoat plasters for Gypsolite, Two-Way Hardwall (National Gypsum products) or other conventional plasters.

Kal-Kore plaster base is sold in 4' and 8' widths and in 8' to 16' lengths - considerably larger than the older plaster-board lath systems shown above and just below where we describe regular rectangular bulges in plaster ceilings and walls.

Board lath and how it is applied are described in Plastering Skills, F. Van Den Branden, Thomas L. Hartsell, and in US Gypsum's Gypsum Construction Handbook as well as other publications. VanDenBranden/Hartsell explain the popularity of board lath as a plaster base [paraphrasing]:

Board lath is rigid, strong, stable, and reduces the possibility of dirt filtering through the mortar to stain the surface
Board lath is insulating, strengthens the framework of the structure, and the gypsum board is fire resistant
Board lath requires the least amount of mortar to cover the surface

Gypsum Board Lath is provided in a variety of sizes, thicknesses, and types, most commonly 3/8" x 16" x 48" in dimension, solid or perforated with 3/4" diameter round holes punched 4" o.c. to provide mechanical keys, improving adhesion and fire rating of the surface. Our photo (above) shows mortar passing through the holes in perforated board lath.

Watch out: only gypsum mortar can be applied over gypsum lath. Never apply lime mortar, portland cement, any other kind of binding agent to gypsum lath. [See PLASTER BULGES & PILLOWS]. Also, perforated board lath should not be used on ceilings where it is supported only at edges, because the perforations weaken the lath.

Gypsum lath board cross section (C) D Friedman

Insulating gypsum lath plaster boards are similar to the gypsum board lath discussed above, but include aluminum foil laminated to the wall or ceiling cavity side of the board. Installed with a 3/4" air space before any ensuing insulation, this material adds about the same R-value as 1/2" insulating board.

Our photo (left) shows a cross section test plug we cut from a finished interior wall in an older home. Oldest materials are on the right side of the plug. From left to right we see

Modern drywall (at leftmost side in the photo)
Insulating gypsum lath board, including
A layer of wood or paper fiber insulating board bonded to the plaster layer

But this is not the only type of plaster lath board or gypsum lath board found in homes. Above left the product includes an insulating layer of up to 1/2" of wood or paper fiber insulating board on its innermost layer. That layer is placed against the wall studs or in a masonry building against the masonry wall.

Our next gyp-lath photo at left illustrates a simpler product installed on interior walls where no insulating layer was desired.

The gypsum-lath board (at left in the photo is made of gypsum covered on both sides by paper - there is no insulating board layer. You can see the thin layer of finish-coat plaster on the right side of this gyp-lath board.

Van Den Branden and Hartsell list ten gypsum board lath products, here we provide the full list

Gypsum lath board - discussed above
Long length insulating gypsum lath
Veneer plaster gypsum lath
Radiant heat gypsum lath plaster base
Gypsum wallboards
Gypsum backer boards
Coreboard
Gypsum studs
Gypsum sound-deadening backer board
Insulating lath board - discussed above

Bulging Plaster Hazards

For a discussion of rectangular bulges, shadow effects, or scalloping in plaster ceilings or walls see PLASTER BULGES & PILLOWS
Watch out: See PLASTER, LOOSE FALL HAZARDS for examples of bulged plaster that may be danger signs, including an example of a collapse of an expanded wire lath ceiling that had been improperly installed.

If you shine a flashlight along, rather than directly at a wall surfaces, both regular details (such as regular, rectangular bulges in a plaster wall or ceiling) as well as irregular surfaces and defects are easily observed.

Details and more examples of this phenomenon are at PLASTER BULGES & PILLOWS

Expanded Diamond 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.

Details about metal lath are found at PLASTER LATH, METAL.

Details about exterior stucco and metal lath are at STUCCO WALL METHODS & INSTALLATION.

Expanded mesh metal lath for plaster walls and ceilings (C) Daniel Friedman

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.

Also see Loose Plaster is Unsafe for an example of a collapse of an expanded wire lath ceiling that had been improperly installed.

Masonry Surfaces as a Plaster Base

Stucco and adobe in Mexico (C) D Friedman S Goldstein

As Van Den Branden and Hartsell detail, "masonry walls are about the oldest form of plaster base known.". Thick coats of lime-based mortar were applied to very rough surfaces to plaster or "stucco" the building exterior or interior surfaces for many centuries before anyone thought of foam-board based EIFS type systems (see SIDING EIFS & STUCCO).

The authors continue to explain that because modern masonry wall exteriors are much more smooth (picture brick or concrete block walls), thinner coatings of mortar are used. The authors define three types of masonry bases for plaster, whether indoors or outside:

Our photo (above left, courtesy of Steve Goldstein) shows both rough and smooth brick and adobe surfaces on buildings in Guanajuato, Mexico.

Wall test cut shows construction (C) D Friedman

And our next plaster lath photo (left) illustrates use of an insulating plaster board applied over a concrete block structure. The masonry block is at left, with a wood frame insert (to hold window trim in this case) followed by (left to right) an insulating board and plaster lath board, finish coats of plaster, all later covered over by modern drywall.

These masonry surfaces are regularly plastered or stuccoed with lime based cement mixtures and should be considered high suction masonry bases as we describe below.

Low suction masonry bases for plaster: glazed tile, hard burnt brick surfaces, road or paving bricks, hard stone such as granite
Medium or average "suction" masonry bases: "cinder block", concrete block, face brick, medium-hard brick, hard clay partition tile, better grades of common brick, and some softer stone surfaces.
High suction masonry bases: soft common brick, soft clay partition tile, gypsum partition tile, some highly porous tile surfaces.

For completeness one should add a fourth plaster surface type:
Concrete surfaces as a plaster base: these surfaces provide special problems for plaster application and need to be specially prepared (scratched), or must be plastered using a special high-adhesive bonding plaster, or coated with a primer that is approved for bonding the plaster to the concrete

See STUCCO WALL METHODS & INSTALLATION for details about exterior stucco wall systems.

Loose Plaster is Unsafe, Especially Loose, Falling Plaster Ceilings

For a discussion of rectangular bulges, shadow effects, or scalloping in plaster ceilings or walls see PLASTER BULGES & PILLOWS
Watch out: See PLASTER, LOOSE FALL HAZARDS for examples of bulged plaster that may be danger signs, including an example of a collapse of an expanded wire lath ceiling that had been improperly installed.

Frequently Asked Questions (FAQs) about plaster ceilings

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Questions & answers or comments about how to identify different types of interior wall & ceiling plaster installation methods & finishes: wood lath, expanded metal lath, plasterboard, & drywall.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - rhankey@hankeyandbrown.com. Mr. Hankey is a frequent contributor to InspectAPedia.com.
America's Favorite Homes, mail-order catalogues as a guide to popular early 20th-century houses, Robert Schweitzer, Michael W.R. Davis, 1990, Wayne State University Press ISBN 0814320066 (may be available from Wayne State University Press)
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, 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/
plastering-technical-guide-veneer-plaster-joint-reinforcement-systems-en-PM5.pdf
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.
Gypsum 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
Metal Lath Specifications, Specification for metal lath and accessories, Lath and Plaster from Amico, a lath and plaster accessory producer.
Lath & Plaster Systems, 092300/NGC, 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, 2001 Rexford Road, Charlotte, North Carolina 28211, Tel: 704-365-7300, Email: ng@nationalgypsum.com, Website: http://www.nationalgypsum.com
MSDS: Gold Bond® brand gypsum board products, plaster base, National Gypsum Corporation. Other drywall MSDS sheets are found at Drywall MSDS.
Metal Lath Specifications, Specification for metal lath and accessories, Lath and Plaster from Amico, 3245 Fayette Ave. P.O. Box 3928, Birmingham, AL 35208, (205) 787-2611, (800) 366-2642 and in Canada: 1080 Corporate Drive, Burlington, Ontario L7L 5R6, Canada, (905) 335-4474, (800) 663-4474. Amico is the largest metal lath producer in North America. Website: http://amico-lath.com/
Weaver: Beaver Board and Upson Board: Beaver Board and Upson Board: History and Conservation of Early Wallboard, Shelby Weaver, APT Bulletin, Vol. 28, No. 2/3 (1997), pp. 71-78, Association for Preservation Technology International (APT), available online at JSTOR.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

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.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

America's Favorite Homes, mail-order catalogues as a guide to popular early 20th-century houses, Robert Schweitzer, Michael W.R. Davis, 1990, Wayne State University Press ISBN 0814320066 (may be available from Wayne State University Press)
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, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print).
Asbestos Identification and Testing References

Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed the basis for current work by asbestos identification laboratories.
Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone

Brick nogging used as soundproofing is mentioned in this article on Popular Forest
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
Construction Drawings and Details, Rosemary Kilmer
"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.
Nogging: See this photo of exposed bricks on a building exterior on a building exterior in Canada. [Thanks to Carson Dunlop, Toronto - see References below].
Pergo AB, division of Perstorp AB, is a Swedish manufacturer or modern laminate flooring products. Information about the U.S. company can be found at http://www.pergo.com where we obtained historical data used in our discussion of the age of flooring materials in buildings.
Manufactured & Modular Homes: Modular Building Systems Association, MBSA, modularhousing.com, is a trade association promoting and providing links to contact modular builders in North America. Also see the Manufactured Home Owners Association, MHOAA, at www.mhoaa.us. The Manufactured Home Owners Association of America is a National Organization dedicated to the protection of the rights of all people living in Manufactured Housing in the United States.
What Style Is It?: A Guide to American Architecture, Rev., John C. Poppeliers, S. Allen Chambers, Wiley; Rev Sub edition (October 6, 2003), ISBN-10: 0471250368, ISBN-13: 978-0471250364
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