Plaster lath board © Daniel Friedman Plaster Types & Methods in Buildings
Plaster Ceilings, Plaster Walls & Plaster Type Identification in buildings
     

  • CEILINGS & WALLS, PLASTER TYPES - CONTENTS: Plaster & plaster lath ceiling types, history, age determination. What are the ingredients in plaster? Does plaster contain asbestos? Did asbestos & horsehair appear together in plaster?
  • POST a QUESTION or READ FAQs 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.

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Guide to Methods & Types of Plaster Ceiling & Wall Covering Systems in buildings

Gyp lath board (C) D FriedmanPhoto Guide to Types Interior Plaster: split wood lath, sawn wood lath, expanded metal lath, "rock lath" or plasterboard, drywall, & tainted Chinese drywall

This article discusses the types of plaster ceiling & wall coverins used in buildings, giving a history and description of types of materials used. We include

  • 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

Also see DRYWALL, PLASTER, BEAVERBOARD 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

PHOTO of hand split lath and plaster ca 1800 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

Sawn wood lath based plaster (C) D FriedmanOur 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.

Plaster lath board © Daniel Friedman Plaster lath board © Daniel Friedman
Mud straw plaster (C) D Friedman

 

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.

Plaster lath board © Daniel Friedman Plaster lath board © Daniel Friedman

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

Plaster lath board © Daniel Friedman Plaster lath board © Daniel Friedman

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.

Plaster lath board © Daniel Friedman 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.

Gypsum lath board cross section (C) D FriedmanWatch 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

  • 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

Gyp lath board (C) D FriedmanBut 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

  1. Gypsum lath board - discussed above
  2. Long length insulating gypsum lath
  3. Veneer plaster gypsum lath
  4. Radiant heat gypsum lath plaster base
  5. Gypsum wallboards
  6. Gypsum backer boards
  7. Coreboard
  8. Gypsum studs
  9. Gypsum sound-deadening backer board
  10. 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.

Plaster lath board © Daniel Friedman

 

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

 

 

 

Reader Question: how to recognize types of plaster board or plaster lath used in buidings

Wall test cut shows construction (C) D FriedmanI 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

Reply: tips for decoding a cross-sectional cut of wall covering to disclose plaster, plasterboard, gyprock etc.

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.

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

  • You may have a home that used plasterboard (or gypsum board) as a lath system to support a finished plaster wall. Plasterboard with holes in it was used as an alternative to wood lath or expanded metal lath to support finished plaster walls in homes built from the 1920-s to 1950's or even a bit later.
  • Asbestos was sometimes used in plaster, and certainly in joint compounds and in some finish textured paints. Even without asbestos, plaster and drywall dust can be a respiratory irritant or hazard, making steps to minimize dust and to control where it goes important, along with proper personal protective gear.

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 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 © 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.

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).

Wall test cut shows construction (C) D Friedman Fiberboard insulating wallboard from a 1944 Minnesota home (C) InspectApedia

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.

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.

  1. Low suction masonry bases for plaster: glazed tile, hard burnt brick surfaces, road or paving bricks, hard stone such as granite
  2. 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.
  3. 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:
  4. 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.

Ingredients in Plaster Used in Buildings

Reader Question: Ingredients in plaster: asbestos, horsehair, other fibers. Plaster chemicalsused in the UK?

(June 23, 2011) Shoe said:

First of all, thank you for this site.

My questions concern horse hair plaster and/or asbestos plaster. My walls and ceilings are wood lathe and plaster that look very much like the photo above from the Wappinger Falls house and the photo next to it. In a few places, the plaster is damaged, very loose, or missing. I've been operating under the assumption that its horsehair plaster; there are visible threads that look like hair. Until today, I wasn't aware of the possibility that there could be asbestos, and from my reading, I'm still unsure of whether that's actually likely. As background, the date of record for the house is 1896 (although I believe that a section of the house may be older, and I guess its possible that some or all of the plaster is newer). The house is located in upstate New York.

So here are my questions:

1) Do asbestos fibers look distinctly different than hair?

2) Is it reasonably safe to assume that the presence of horse hair indicates that there probably isn't asbestos? (I've read this claim in forums, but the authors were speculating, not speaking from experience.) What about the powdery asbestos?

3) I read that OSHA guidelines requires that all troweled plasters must be treated as presumed asbestos containing material (PACM). Does that apply to my plaster? What does that mean if I want to hire a contractor to do any work in the house?
Thanks for your help,
Shoe

12/06/2014 aw said:

would lathes in 1930 UK houses that were used for plastering ceiling been treated with any type of chemical?

Reply:

Shoe:

About the risk of asbestos use in horsehair based plaster, Gman has made an important point: that material was used into the 20th century so some versions may include asbestos even though asbestos was not in common use in plaster in the earlier 1800's.

I'd respect OSHA's guidelines, and in particular, do not allow a contractor to make a dusty mess in any building if the mess might contain asbestos - not only are there health risks but you're risking a more costly cleanup project than if the material were handled properly in the first place.

What this means in a practical sense is that ANY restoration or renovation work in your home could be much more costly once you notify the contractor that the walls and ceilings may contain asbestos-containing plaster.

Because of that risk of added cost, it would be worth having a few representative plaster samples from your home tested by a certified asbestos testing lab. Individual tests are not expensive, typically costing less than $50. each. If the tests indicate that your particular plaster is asbestos free, you will significantly reduce the cost of renovations and repair work on those surfaces.

- Moderator

(June 27, 2011) Gman said:

Horse hair plaster has be known to contain Asbestos as a bonding matrix, although I'm not entirely sure how common Asbestos use was in the late 1800's. Horse Hair plaster was used right through the 1800's until even the mid - late 1950's.

It was mainly during the period between 1920 and World War 2 that asbestos was the material of choice way up until the late 80's and it was contained in a lot of things - even talcum powder!!! If your house was built from between 1920 - 1950 I would pressume there would be some asbestos within the hair hair plaster as a bonding agent, maybe ranging from about 1% - 10%. Anything containing asbestos at 1% isn't considered an asbestos material as it is fairly harmless. The fact you live in America might add to the risk as asbestos was more widely used and manafactured in the US more than anywhere else!!

Asbestos will softly crumble in your hands, it will be powdery and you will see tiny needle like hairs (distinctively different from long coarse horse hair)emerging from the substance.

It is definetly correct and safer to treat all troweled plasters with cautuion because 95% of the time they do contain asbestos!! Better being safe than sorry as they say!

You sound very sensible and well done for taking this seriously.

I highly advise you to send a sample off to a contractor or asbestos removal company, they examine and run tests on each sample for about £20 - £30 or in your case $30 - $45 per sample. Its always best to call out a contractor to remove the sample piece for you - in the UK this is usually free of charge, I dont know about the US.

Asbestos removal is very pricey which is why people try to avoid it...bodge it themselves...and then end up dying about 30 years later!

Reply to AW: common constituent ingredients in plaster

AW

Not that I've come across in research - but speaking more generally, water is a chemical as are normal ingredients in plaster. Hydradted lime - gypsum - water. Adapting from Wikipedia and other sources on the ingredients in plaster,
Lime-based plaster such as that found in UK homes is a mixture of calcium hydroxide (lime) and sand (or other inert fillers). Carbon dioxide in the atmosphere (in other words on exposure to air as the plaster sets and dries) causes the plaster to set by transforming the calcium hydroxide into calcium carbonate (limestone or CaCO3). Incidentally, whitewash is based on the same chemistry but was applied as a thick white paint on building interiors or exteriors.

If you could be more specific about your concern and the reasons for it we may be able to offer some suggestions.

Question: hard gray substrate below plaster

(June 1, 2014) Chris said:

While clearing away the damaged ceiling covering, I discovered a grey hard substrate "below" the white thin plaster-like veneer. The home was built in the 1950s. Inspecting the back of these ceiling boards from the attic, I found brownpaper-backing with numbers printed on (includes 5PH). My guess is that I have a plaster over cement board ceiling, correct?

Reply: scratch coat or rock lath base for finish plaster surfaced walls & ceilings

The gray substrate you see is probably the "scratch coat" on which the finish coat was applied. Or plaster may have been applied over cement board as you infer.

(June 1, 2014) Chris said:

Thanks, DanJoeFriedman, pretty sure that a 1/16" plaster application was made to a cement board with brownpaper-backing--the white plaster-like material came away cleanly in shards using a putty knife. The consistent thickness of the plaster application makes me wonder if the boards came with it factory-applied back in those days (presuming the ceilings are original, which I don't know). I plan to apply a bleach-water mixture to the discolored cement area where the water came through, use a mortar caulk/sealant in the cement board crack, and use joint compound to replace the scraped away plaster.

Reply:

Chris, Yes it sounds as if you're looking at a version of rock lath - a plaster board that was used as a base for a finish coat of plaster applied by hand.

 

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