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. Synonyms for "plaster" include stucco, render, lime plaster, cement plaster, gypsum plaster, and plaster of paris. Lime plaster is also the principal ingredient in whitewash often used on building stone walls both indoors and outside and also sometimes applied to wood surfaces.
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Photo Guide to Types Interior Plaster: split wood lath, sawn wood lath, expanded metal lath, "rock lath" or plasterboard, drywall, & tainted Chinese drywall
This article includes a photo guide to split wood lath, pit-sawn lath, circular blade sawn wood lath, expanded metal lath, "rock lath" or plasterboard, drywall, & tainted Chinese drywalldiscusses the types of plaster ceiling & wall coverins used in buildings, giving a history and description of types of materials used. We include a description of plaster system identification and history of use of plaster, a photo guide to plaster coatings, cracks, hazards, and plaster ceiling collapse hazards & photographs
Also see DRYWALL, FIBERBOARD, PLASTER INTERIORS where we include photographs of non-plaster interior wall and ceiling coverings including drywall, beaverboard, and paneling.
See DRYWALL ASBESTOS CONTENT for a discussion of asbestos in joint compound used on gypsum board systems for finishing joints, skim coats, possibly in gypsum-board plaster systerms and other applications.
Also see drywall identification photos at CHINESE DRYWALL HAZARDS.
For plaster type surfaces used on building exteriors, see STUCCO WALL METHODS & INSTALLATION.
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 (above 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;
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.
Above we show a mud-straw mix of plaster base coat used in a late 18th century New York home, ca 1785.
Our plaster wall and ceiling photos below demonstrate the stages in constructing an traditional plaster on lath surface. The principal differences between 3-coat plaster and 2-coat plaster systems are the inclusion or omission of the second intermediat coat that we discuss below. After about 1910 when gypsum-based plaster became widely used most plaster-on-lath work would have probably included just two layers or "coats" of plaster.
Three-coat plaster was applied in three layers from most-coarse to most fine. When applied over wood lath or later, metal lath, the first coat of plaster, the brown coat or scratch coat, is pushed through openings in the lath so that when it hardens it is mechanically secured to the building wall or ceiling. Below is a photo of the base coat of plaster viewed from the other side of a hand-split lath wall in a pre-1900 home I restored.
The base coat was very coarse and was referred to as a scratch coat or brown coat. Sometimes in attics and basements just the brown coat or scratch plaster coat was applied, which is why I was able to take the photo shown just below. The gouges or scratches in the brown coat were made by the plasterer using a notched tool or saw-tooth-edged tool to improve the adhesion of the next coat. The first two plaster coats would each be about 3/8" thick while the final coat was quite thin, just 1/8" in thickness.
Our plaster scratch coat or "brown coat" photo (below) 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 [Image file].
The second coat of plaster in a three coat system was used to bring the surface of the finished wall forward and add thickness before applying the thinner, smoother finish coat.
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.
In a two or three-coat plaster system the final top coat was intended to be troweled smooth and typically would have included the highest lime or gypsum content of the two or three layers. Typically the top coat is just 1/8" thick.
Spray-on plaster coatings, widely used as a fireproofing in ships and buildings were more likely to include asbestos as well as rock wool, vermiculite, and fiberglass. Asbestos was been used in other plaster preparations too. Spray-on plaster ceiling coatings beginning much later (perhaps in the 1960's  included styrofoam or similar beads or fragments.
Celotex and other brands of fiberboard sheathing were used both as exterior wall sheathing and as interior wall sheathing or as a base for plastering as we describe below. More about these products is
at FIBERBOARD SHEATHING IDENTIFICATION
Look closely at the photo above [Click to enlarge any image] and you can see what looks like a first layer of fiberboard below the plaster to which my pen is pointing.
Celotex recommended its use also as a base for plaster walls or ceilings, for which some installation instructions can be read in the image just below. Thanks to reader [Anon by private email 21/14/15] for this image.
[Click to enlarge any image]
The Celotex instructions for use of this fiberboard as a plaster lath base include some interesting details for Celotex applied as a plaster base. These plastering instructions were provided by the Celotex Company in Chicago and were affixed to Celotex fiberboards from the New Orleans Plant [and perhaps others].
Quoting Celotex in italics, we include additional explanation or speculatino in the [bracketed comments]
[A number of these instructions suggest that over-wetting or prolonged wetting of these boards might lead to swelling, weakening, buckling, bulging, or other issues in the finished plaster job.]
From our own field inspections, we believe that Celotex insulating lumber or similar products were indeed also often left exposed as an interior finish most commonly in summer camps, cottages, and in commercial or farm buildings.
According to one source the material was also used to construct insulated shipping boxes.  By 1925 Celotex had published "Celotex insulating Lumber Specifications and Details for Standard Building Board" and also offered "Your Home" a plan book of twenty-five ideal small homes. A review of the patents and product description for Celotex insulating lumber products shows that asbestos was not among the product's ingredients.
Our photo (above) shows perforated gypsum board panels that were used as plaster lath.
Solid gypsum board (above 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.
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
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
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
I am not sure if you can help. I have looked up infor online and csn not find any. My home was built in 1922. I have stripped wall paper that was hung in 1959. Under the paper I thought id find lath and plaster. Not so much. The look is that of sheet rock but at close inspection it is more like concrete.
Like morter I guess. You can scrape it away and it comes off like sand. It seems thick maybe 1/2 inch. I am wondering what it is and is it dangerous. The walls are all in excellent shape with minor patch work. My grandparents lived here since it was built both lived long healthy live. But ya never know. Any info would be helpful. Thanks. - B.D. 6/19/12
Our photo (above left) shows layers of wall finish material in a masonry block home: concrete block at left, wood insert to secure window trim (removed for the photo), a wood fiber insulating board or "beaverboard" type material, a layer of plaster, layers of finish plaster and paint, and finally at right, modern drywall. But normally one cannot see these layers oif material except where there is a cross-sectional cut into the wall.
See FIBERBOARD PLASTER BASE SYSTEMS for a description of how fiberboard was used as a plastering base.
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem material in building interiors. That said, here are some things to consider:
I'd need to see photos and perhaps a sharp photo of a test cut through the wall material to have a more confident view of how your wall was constructed but
If all that's needed are minor repairs to the finish wall surfaces and you are adding a patch not demolishing the walls, leaving the existing material in place is not itself a hazard. Asbestos is not radioactive - it does not emit harmful particles unless it is disturbed. In a home of this age it would be resonable to treat these materials as Presumed Asbestos Containing Materials (PACM) as well as to assume that lead paint hazards are present.
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.
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.
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.
And our next plaster lath photo (left) illustrates use of an insulating plaster board applied over a concrete block structure.
In the photo at below left a masonry block structural wall is at far left, with a wood frame insert (to hold window trim in this case) followed by (left to right) an insulating brown fiber-board used indoors as wallboard or as a lath-substitute backer for plaster, and then a scratch coat and finish coats of plaster. Paint and possibly wallpaper were applied over the original plaster and are seen to the right of my pen.
All of that original finished wall later covered over by modern drywall. My pen point indicates the first plaster rough coat applied over the wood-product brown fiberboard backer (in shadow just to the left of the pen).
At above right is a reader-contributed photo showing original fiberboard or "brownboard" interior wall sheathing used as a "lath" base for a rough-coat (white) and finish coat of plaster. More about these surfaces is
at FIBERBOARD SHEATHING.
If you are unsure about identifying fiberboad sheathing products
see FIBERBOARD SHEATHING IDENTIFICATION
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.
See STUCCO WALL METHODS & INSTALLATION for details about exterior stucco wall systems.
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.
This topic has been moved to PLASTER INGREDIENTS, MIX, COMPONENTS
Shown below, horsehair plaster applied to a stone basement wall of an 1870 home located in up-state New York.
The homeowner had a sample of this plaster tested for asbestos and reported:
Just to update you. The hairy plaster came back negative for asbestos. The insulation around the pipe [referring to a white sealant paste around the connection of a flue vent connector to a masonry chimney] was 40% Chrysotile. - Anon [by private email] 2015/12/22
[See ASBESTOS PHOTO GUIDE to MATERIALS for a description of furnace cement and asbestos paper used on ducts and flue vent connectors in buildings - Ed.]
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11/5/2014 Gerard Gonzalez said:
I own a old house with plaster lath walls. The walls are starting to show signs of cracks. I also believe that there is limited to no insulation behind these walls. I was told that covering up the old walls with drywall is a better solution, due to the amount of work that comes with demoing plaster walls. I was wondering if covering the plaster walls with drywall would be a good solution? Also is there anything I can place between the new drywall and old plaster wall that will provide me with better insulation?
Laminating a layer of drywall over old plaster is common, is fine, as long as there are not cosmetic issues with burying window and door trim.
You will still have to build out every electrical outlet, wall switch, and light fixture box for proper and safe electrical wiring practices.
Adding a layer of drywall (you could even use lighter 1/4" thick material) over plaster indeed avoids the demolition mess, thus is faster and cheaper.
However that does not address the insulation question. You might consider
1. First, obtain a more accurate assessment of the extent and type of building insulation present - if any.
2. Based on 1., obtain bids on blowing in insulation into walls - from outside or from inside.
3. If insulation is to be blown-in to the building from inside the time to do that is before installing your layer of drywall over the older plaster walls and ceilings.
Indeed instead of blowing in insulation (the most effective approach and one that usually minimizes air leakage) you could
- install a radiant barrier between the new drywall and old plaster (slight benefit)
- install a layer of 1" high-R solid foam board insulation between the old plaster and new drywall - figure a maximum of r-8 per inch which will be less than if you blow insulation into a 3 1/2" deep wall cavity; this approach will certainly add to the finish work on the interior as in addition to building out the electrical components I cited above, you'll have to build out or remove and replace all trim in the rooms: windows, doors, floor, ceiling.
- install solid foam insulation over furring to give an air space to increase the R-value of the wall - same extra work as the option I just cited.
If you consider the amount of labor in these additional higher R- approaches to wall insulation, the appeal of blowing into the walls increases.
(Feb 19, 2015) Eric Thomson said:
Is there any visual clue to determine if an existing expanded metal lath wall system used gypsum-sand plaster or portland cement-sand plaster? I am trying to determine an equivalent fire rating for the assembly. (wall: 7/8" plaster + 4' steel truss stud + 7/8" plaster) (ceiling: 7/8" plaster on expanded metal lath supported by black iron w/ wire ties)
I don't know and will research a bit. A preliminary guess is that cementious materials containing Portland cement woul d show as more gray.
(Mar 27, 2015) David Hunter said:
My home was built in 1927. The interior walls are plaster over wood laths & mesh. The house is damp in the winter and heat is all upstairs. We like the hard plaster walls and don't want to remove them. Is it possible to insulate the interior plaster walls. Can we use drywall over the plaster walls? Will this work? What are the available methods, techniques or materials we can use to reduce dampness and increase insullation. Thank ypu for any advice.
Sure you can insulate an existing wall cavity: you can have an insulation contractor blow-in cellulose, chopped fiberglass (maybe), or foam by making appropriate openings from outside or inside the building.
Sometimes it's easier to lift off a few siding boards than to cut and fix and re-paint inside.
(Sept 3, 2015) Dr manisha jaiprakash said:
Why is plaster of paris put on newly laid floor tiles during ongoing renovation of interiors
It is not - though I imagine someone might think that's a way to protect the floors from damage - but it'll be heck to get off.
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