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ASBESTOS IDENTIFICATION IN buildings
BASEMENT CEILING VAPOR BARRIER
BATH & KITCHEN DESIGN GUIDE
BEST CONSTRUCTION PRACTICES GUIDE
BOOKSTORE - INTERIORS
BRICK LINED WALLS
CABINETS & COUNTERTOPS
CARPETING, SELECTION & INSTALLATION
CASEWORK, CABINETS, SHELVING INSTALLATION
CATHEDRAL CEILING INSULATION
CEILING FINISHES INTERIOR
CEILINGS & WALLS, PLASTER TYPES
DRYWALL INSTALLATION Best Practices
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
FLOOR TYPES & DEFECTS
FLOORING MATERIALS, Age, Types
HEAT LOSS in BUILDINGS
HOUSEWRAP AIR & VAPOR BARRIERS
HOUSE DOCTOR, how-to be
HOUSE PARTS, DEFINITIONS
HUMIDITY LEVEL TARGET
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INTERIOR FINISHES, BEST PRACTICES
KITCHEN & BATH DESIGN GUIDE
LIGHTING, INTERIOR GUIDE
MAINTENANCE SCHEDULE & PRIORITIES
MOISTURE CONTROL in BUILDINGS
MOLD: A COMPLETE GUIDE TO MOLD
NOISE / SOUND DIAGNOSIS & CURE
ODORS GASES SMELLS, DIAGNOSIS & CURE
PAINT & STAIN SELECTION & PROCEDURES
PLASTER & BEAVERBOARD & DRYWALL
ROOF VENTILATION SPECIFICATIONS
SAFETY HAZARDS & INSPECTIONS
STAIN DIAGNOSIS on BUILDING INTERIORS
STAIRS, RAILINGS, LANDINGS, RAMPS
STUCCO WALL METHODS & INSTALLATION
SWEATING (CONDENSATION) on PIPES, TANKS
VAPOR BARRIERS & CONDENSATION in buildings
VENTILATION in BUILDINGS
WALL FINISHES INTERIOR
WATER ENTRY in buildings
WINDOWS & DOORS
WINTERIZE A BUILDING
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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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 discusses the types of plaster ceiling & wall coverins used in buildings, giving a history and description of types of materials used. We include
Also see Plaster & Beaverboard & Drywall where we include photographs of non-plaster interior wall and ceiling coverings including drywall, beaverboard, and paneling.
Plaster Ceilings & Walls Applied over Wood Lath
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.
At left 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. 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.
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
Bulging Plaster Hazards
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 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. 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.
See STUCCO WALL METHODS & INSTALLATION for details about exterior stucco wall systems.
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