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 Bulges & Shadow Effects in Plaster Ceilings & Walls - the "Shadow Effect"
- PLASTER BULGES & PILLOWS - 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 recognize & diagnose loose or bulged plaster ceilings or walls, causes, hazards, recommendations
- References
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Here we provide a photo guide to identifying types of plaster 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. Page top photo provided courtesy of Minneapolis home inspector Roger Hankey.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
How to Identify & Diagnose Pillow Effect Bulging Found on Plasterboard Lath (Rock Lath) Ceilings & Walls
Also see PLASTER, LOOSE FALL HAZARDS, and see PLASTER TYPE IDENTIFICATION and 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. Also see BUILDING SAFETY HAZARDS GUIDE for more building hazards of particular concern to homeowners or building contractors, building inspectors, and home inspectors.
Shadowing bulged walls traced to gypsum lath installation: as our photos show, below, the wall in this New York home was bulged in a regular rectangular pattern. The building owners were concerned for possible exterior leaks into the wall cavity and a hidden mold problem.
Because the home had experienced leaks in other areas and had other mold problems we investigated further. But the bulged wall problem in this case was essentially a cosmetic one identified and described as plaster wall shadow effect discussed below.
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.
In this photo you can see the convex vertical plaster wall bulges and the indentations at the plaster lath-board points of nailing to the wall studs. More about using oblique light to find building conditions is at FLASHLIGHT HELPS FIND MOLD.
Minnesota inspection expert Roger Hankey has provided our next photograph, below, where the oblique light source was from a window at the right side of the picture. |
Shadow Effect in Bulged Plaster Ceilings
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ASHI home inspector Roger Hankey has provided us with the image of regularly-bulged rectangular plaster ceiling panels shown at left in a home built in 1947. Mr. Hankey includes the following explanation:
Here is the image for the "pillow effect" ceiling from the rock lathe panels. From the ASHI SmartTrack lesson on this topic Hankey quotes:
Shadow Effect A common problem with plaster applied over gypsum lath is the shadow or bulge effect. This was created when the plaster was applied too quickly. The finish coat was sometimes applied before the first coat dried completely. The moisture was driven back into the gypsum lath which sagged. The result is a pattern visible in the wall or ceiling that shows seams every sixteen inches in one direction. Sometimes seams are also visible perpendicular to these, at thirty-two or forty-eight inch intervals. |
Compare bulged pillowed plaster ceiling with sagged 16 x 32-inch ceiling tiles?
At ASBESTOS CEILING TILES - in the article FAQs section we discuss the possibility that the material shown at left, apparently 16" x 32" water-damaged ceiling tiles may contain asbestos and what to do about it.
The ceiling shown was found in home built in the 1940's. |
Doubts about plaster shadow sagging cause & a vote for bulging
 OPINION-DF: The SmartTrack explanation above leaves us a little unsure of the sagging plasterboard diagnosis even though we agree that visually, it's a "sag". Take another look at our bulged wall photograph above.
And check the Carson Dunlop Associates explanation of the shadow effect on building walls (left).
The identical bulging pattern appears on a vertical surface, with the convex side of the bulge facing into the room.
While it's natural to suspect weight-driven sagging on a bulged plaster ceiling, gravity cannot not explain the roomwards bulge of the same pattern in a gypsum-lath wall.
Indeed in their Gypsum Construction Handbook, 2d ed. p. 339, USG describes a cause of ceiling panel sagging but does not address the identical bulging in wall panels:
Panels - Board Sag:
a. Cause: too much weight from overlaid insulation; exposure to sustained high humidity; vapor retarder improperly installed or wetting causes ceiling panels to sag after installation. Also caused by installing board too thin for framing spacing.
Remedy: remove sagged board or fur ceiling using RC-1 Resilient Channels and apply another layer of board.
Prevention: ... proper frame spacing and application procedures
b. Cause: Water-based textures wet face paper and weaken gypsum core, causing ceiling panels to sag after installation
Remedy: same as above.
But these causes do not address wall bulging, nor are the remedies complete as cause and cure of excessive interior moisture are not addressed. Further not all mistakes that might cause bulging or failures in board-lath plaster walls and ceilings are addressed, for example use of portland cement based plaster on gypsum board lath, or using perforated board lath on ceilings - two mistakes we discuss at PLASTER TYPE IDENTIFICATION.
We offer an alternative explanation may explain the plaster pillow bulge, at least on walls: a too-wet, too thick, too-slow-drying second or finish coat of plaster applied over the gypsum board lath may have caused both softening (the sagging theory) and swelling-buckling away from the nailed edges (swelling-buckling theory). Wet, humid weather conditions at the time of installation may have been a factor.
A useful ingredient in understanding observations of anomalies or defects buildings is the recognition of the presence or absence of uniformity. We must ask, why is this particular wall or ceiling bulged and not that one? Were they built at the same time, using the same materials? Really identical materials? What is different in and out of the anomalous area? If we can understand completely all of the forces at work, individual building defects will no longer include an element of chance.
We also considered exposure to subsequent wetting events as a possible explanation for plaster sagging. The regular rectangular pattern surely has at its root the original panel size and the fact that panel edges were nailed to ceiling or wall joists or studs.
Modern plaster board joint shadowing
Buckled gypsum board products, including modern drywall, are often observed to have deformed when wet along with their refusal to return to a flat position when dry. Indeed shadowing is described in gypsum product manufacturer's literature such as USG's "Plastering", and shadowing remains a cosmetic concern at joints in modern gypsum-board based plaster systems. To avoid modern shadowing at plaster board joints, two coats of veneer plaster are required at the tape joints and must be allowed to harden and dry before the plaster application is started. But we think that applying this description to the bulged plaster board lath panels above may be an error.
An accurate understanding of the etiology of construction defects is important in forming a reliable opinion about their import as well as their cure or prevention. Many construction explanations mistake confidence for authority and expertise. We're researching this question and will post further results here - Ed.
Other Interior Wall "Shadowing"
US Gypsum in the Gypsum Construction Handbook (2d Ed. p. 339) provides a completely different definition of shadowing, quoting:
[Definition of] Finish-Shadowing:
Cause: Temperature differentials in outside walls or top-floor ceilings causes collection of airborne dust on colder spots of interior surface, resulting in photographing or shadowing over fasteners, furring, or framing. Most severe with great indoor-outdoor temperature variation.
Remedy: Wash painted surfaces, remove spots with wallpaper cleaner, or redecorate surfaces; change air filters regularly.
Prevention: Use double-layer application with adhesively applied face layer. Use separately framed free-standing interior wall surface and insulate in void to reduce temperature difference between steel or wood components and panels.
[This definition and explanation are incomplete, see THERMAL TRACKING Indicates Heat Loss for details - Ed.]
Watch out: although the ceiling in Mr. Hankey's photo (above) may be soundly secured, other cases of bulged plaster are unsafe. 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.
Details about exterior stucco and metal lath are at STUCCO WALL METHODS & INSTALLATION.
Also see
- ASTM C 842
- ASTM C 841 Metal Lath or gypsum lath installation
- 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]
- 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
- Metal Lath Specifications, Specification for metal lath and accessories, Lath and Plaster from Amico, a lath and plaster accessory producer.
Frequently Asked Questions (FAQs) about plaster ceilings, ceiling materials, and pillowing or sagging pattern diagnosis
Question: is it ok to plaster over "beaver board" ?
 Can I plaster over beaver board ? - Richard
Reply:
Richard, as our photo (above left) shows, people have indeed installed plaster directly over wood-fiber insulating boards, such as in the concrete building in our photo. But in general, I'd be concerned that the beaverboard may not not a good base for plaster finished walls or ceilings installed in a wood-framed structure for these reasons
- beaverboard is likely to be too flexible- leading to plaster cracking
- possibly you may also have bond strength problems; normally the plaster base coat depends on mechanical adhesion (plaster ears pushed through the lath or through holes in the plasterboard)
- you may find severe bleed-through and brown staining of the finish plaster surface
I'd consider installing a laminate of drywall over the beaverboard instead.
Also see
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.
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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?
"
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.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:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
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 Home Reference Book, a reference & inspection report product for building owners & inspectors.
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.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & 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.
- 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.
- 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.
- 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
 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.
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- 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
- 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
- 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.
- Piquet Wall Construction: See this photo of
piquet wall construction - involving timber-framed wall construction with long top girts, diagonal timber bracing, and small diameter logs
placed vertically along with concrete chinking to fill in the wall plane.
- Rubblestone Wall Filler: See this Lartigue House using exterior-exposed rubblestone filler between vertical timbers of a post and beam-framed Canadian building.
- 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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