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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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
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
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.
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.
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]:
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.
Bulging Plaster Hazards
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.
Frequently Asked Questions (FAQs) about plaster ceilings
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.