Nail pop mechanism in walls (C) Carson Dunlop Associates Interior Wall Finishes
How to Inspect, Diagnose, & Repair Problems in Building Interior Walls

  • WALL FINISHES INTERIOR - CONTENTS: Definition and illustration of types of interior wall finishes and systems: types of plaster walls, drywall, brick, stone, and paneling.
    • Catalog of common interior wall defects, how they are recognized, what causes them. Water damaged or stained interior walls. Cracks in interior walls. Plaster cracks, loose plaster, falling plaster. Mold on interior wall surfaces.
  • CEILING FINISHES INTERIOR - separate article
  • DRYWALL NAIL POPS - separate article
  • TRUSS UPLIFT, ROOF - separate article
  • POST a QUESTION or READ FAQs about cracks and nail pops in interior building walls & ceilings, plaster, drywall, etc.

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This article describes the major wall finishes used in buildings and identifies common problems in, and repair of building interior walls. We also discuss interior wall and ceiling cracks, nail pops, concerns for movement and hidden structural damage. Information is provided about visual clues of building condition, such as evidence of a history of leaks, as well as evidence of hazardous materials and conditions such as the probable presence of animal allergens, asbestos, or mold.

We discuss how to identify and correct various building leaks, moisture, and venting problems such as ice dams, blocked attic ventilation, excessive indoor humidity, how to prevent indoor mold, and how to respond to building floods and similar emergencies. The drawing at page top of nail pop causes is provided courtesy of Carson Dunlop Associates.

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Interiors Wall Finishes: Types, Defect Recognition, Repair for Building Interiors

Inspecting an interior wall (C) Carson Dunlop AssociatesThe following building interior wall finish type descriptions, and interior wall defect descriptions are adapted and expanded from original citations provided courtesy of Carson Dunlop Associates, Home Reference Book, with permission.

The sketch at left illustrates two simple methods for inspecting interior walls or ceilings for common defects: use of parallel or oblique lighting (see for details) and tapping. The drawing is provided courtesy of Carson Dunlop Associates and appears in their Illustrated Home.

[Click to enlarge any image]

At USING LIGHT TO FIND MOLD we provide a detailed example and procedures for using lighting to find otherwise hard-to-see building defects.

Types of Major Wall Finishes Described

Wall finishes provide a decorative skin to conceal building components including structural members, insulation, ductwork, pipes, and wires.

Good wall finishes are plumb and straight. Surfaces may be smooth or textured and better wall finishes are durable. Some wall finishes are versatile, taking decorative finishes such as stain, paint or wallpaper readily.

Walls may make a decorating statement, or may be simply background. In some cases, the combustibility of wall finishes may be an issue. In kitchens and bathrooms, resistance to water damage is an asset.

Plaster / Drywall Wall Materials, Types, Properties

Plaster and drywall are essentially the same material. Drywall is manufactured while plaster is mixed and applied by trowel on site. Plaster and drywall are made largely of gypsum, a common mineral (calcium sulphate hydrate).

These interior finishes are very common because they are inexpensive, relatively easy to apply, stable and afford good fire resistance. See details about plaster, beaverboard, and drywall interior wall materials at DRYWALL, PLASTER, BEAVERBOARD. Also see PLASTER TYPE IDENTIFICATION, and for modern drywall concerns also see CHINESE DRYWALL HAZARDS.

At our AGE of a BUILDING - how to determine article series we explain how you can guesstimate the age of a building by taking a look at its wall construction and finish materials. For example, in rough order walls were finished using hand-split wood lath, sawn lath, expanded metal lath, gypsum board lath, and drywall. These materials are easy to recognize and identify, as we illustrate here.

Wood Lath Based Plaster Walls

Plaster lath board © Daniel Friedman

Older plaster systems employ a wood lath, comprised of boards roughly one inch wide by 1/4 inch thick. These “yardstick” type boards were nailed to the studs or strapping horizontally, with roughly 1/4 inch spaces between each board. The plaster was then toweled on in two or three coats.

Our wood lath plaster photo (left) takes advantage of some loose plaster to show the wood lath strips to which the plaster was applied.

The first coat of plaster would ooze through the spaces between the wood lath, sag, and harden to form a “key” which held the plaster onto the lath. This first layer is called a “scratch” coat [photo]. More wood lath wall and ceiling photos and details are at PLASTER TYPE IDENTIFICATION.

Where a three-step process is used, the second coat is called the “brown” coat and the third is a “finish or putty” coat. In a two-step process, there is still a scratch coat and a brown coat, but they are applied one immediately after the other. The finish coat is applied after the brown coat has set.

Wire Lath Supported Plaster Walls

Expanded mesh metal lath for plaster walls and ceilings © Daniel Friedman

Wire mesh lath was sometimes used where reinforcing is necessary, for example, on door frames and comers.

Wire lath was also used in some bathroom areas where ceramic tile was to be provided. Details about wire lath are found at PLASTER LATH, METAL.

Gypsum Lath Supported Plaster Walls

Gypsum lath compared with drywall (C) Carson Dunlop Associates

In the 1930s, gypsum lath became popular. These manufactured plaster sheets replaced wood lath because they were quicker and less expensive to install. The gypsum lath was paper covered, similar to drywall.

Gypsum lath panels or boards came in various sizes, but was typically 16 inches by 48 inches. The gypsum lath was covered with one or two coats of plaster and the total thickness of the system was 1/2 to 5/8 inch. The lath itself is typically 3/8 inch thick.

Here is a photograph of gypsum lath board from our PLASTER TYPE IDENTIFICATION article.

See PLASTER BULGES & PILLOWS where we include diagnostic photographs of pillowed gypsum lath ceilings.

Also see PLASTER VENEER Best Practices.

The drawing at left is provided courtesy of Carson Dunlop Associates and appears in their Illustrated Home.

Drywall Use for Interior Walls & Ceilings

Because both gypsum lath and drywall use a factory-made gypsum panel, there can be confusion about the difference between these two systems. The sketch at left, explains how these wall systems differ and is provided courtesy of Carson Dunlop Associates and appears in their Illustrated Home.

Drywall became popular in the early 1960s, and is used almost exclusively today. There is very little difference between properly executed drywall and plaster jobs. Poor drywall work is usually identified at the seams. Sections of drywall are typically four feet by eight, ten, 12, or 14 feet.

Drywall is typically available in 3/8 inch, 1/2 inch and 5/8 inch thicknesses. Special drywalls, more resistant to water or fire, are available. Drywall is typically nailed or screwed onto framing members.

The seams between drywall panels are taped and filled with drywall compound (also called joint compound, drywall mud and taping compound). The joints are wet (avoids dust) or dry sanded when they dry to create a homogeneous wall surface. If the taping and finishing work is poor, the drywall seams are noticeable. Drywall is also called wallboard, sheetrock, plasterboard and gyprock.

Paneling on Interior Walls

Wall paneling may be veneered plywood, asbestos-cement board, veneered particle board, or solid wood. It is available in many forms and appearances, from a simple and inexpensive 1/8 inch sheet of 4x8 plywood, to an intricate, highly finished hardwood system, found in dining rooms and libraries of high quality homes.

Wall paneling is often more durable than a plaster or drywall finish, although wood materials move more than drywall as a result of expansion and contraction. These finishes can be considerably more expensive than drywall. In some applications, the combustibility of this material may be an issue.

Most paneling does not take paint or wallpaper as readily as drywall or plaster. Redecorating paneling can be difficult without removing it. Some paneling is difficult to patch without leaving any evidence.

Brick or Stone Surfaces on Building Interior Walls

Brick or Stone are not common interior wall finishes in homes, though we do find brick or stone veneers in kitchens, dens, around fireplaces, and in similar locations.

Some work on old homes includes removal of original plaster to expose brick on walls. This brickwork was usually not intended to be viewed, and may show a large number of small, damaged or off-colored bricks. Mortar joints may be quite irregular. Removing plaster from the inner face of an exterior brick wall reduces the insulating value of the wall slightly, and can make the room less comfortable in cold climates.

Removing plaster from an interior brick wall does not pose the same problem, although it does reduce the acoustic insulating properties of the wall. This may be an issue, for example, on attached homes with a common brick wall. Sealing exposed brick walls helps control the dust from the bricks and mortar.

Thin slices of brick or stone roughly 1/2- inch thick, or imitation brick can be applied to a wall using an adhesive or embedding the brick in mortar. They may be individual pieces or larger panels. Slices are sometimes used around fireplace openings to create the effect of solid masonry. Full bricks are not used because their weight would require strengthening the floor below.


Concrete/Concrete Block Interior Wall Surfaces

These materials are associated with unfinished walls, typically in a basement. They can be painted to provide a more finished appearance. Concrete is strong and these walls are unlikely to be damaged as a result of normal usage.

See FRAMING DAMAGE, INSPECTION, REPAIR for details about all types of cracks in masonry walls and floors, including concrete and concrete block.

Stucco/Textured Interior Wall Finishes

Interior stucco is essentially plaster, and is typically installed in a two or three coat process. The finish is often sculpted or worked to provide a decorative appearance. The texturing is done with trowels, sponges, brushes, or other tools to give the desired effect.

See these stucco articles for details: STUCCO WALL METHODS & INSTALLATION, and STUCCO OVER FOAM INSULATION (on exteriors), and STUCCO PAINT FAILURES (on building exterior or interior walls).

Common Interior Wall Finish Problems

Water Damaged or Stained Interior Walls

Delmhorst pin type moisture meter with long probes © Daniel FriedmanWater damage is one of the most common problems on interior finishes. It is helpful to know

  1. the source of the water,
  2. whether the problem is still active,
  3. whether there is any concealed damage
  4. the cost to correct the water problem if needed, e) and the cost to repair the damaged building materials.

Common water sources include roof leaks, flashing leaks, ice damming, window and skylight leaks, plumbing leaks, leaks from hot water heating systems, and condensation.

Water damage may also result from such things as aquariums, room humidifiers or dehumidifiers, over-watering of plants, spills, melting snow and ice from boots during wintertime, et cetera.

Water damage often looks more serious than it is. Short term exposure to water will not harm most building materials. Plaster and drywall however, are easily damaged by water. Stains appear quickly and persist after the problem is solved. The material that can be easily seen is the first material to deteriorate. Mold can develop on the front or back surface of plaster or drywall if it is chronically wet. Mold will not disappear but will go dormant if the moisture source is removed.

See complete details about building water entry beginning at WATER ENTRY in BUILDINGS.

For a complete guide to diagnosing stains on building interiors see STAIN DIAGNOSIS on BUILDING INTERIORS.

Chinese Drywall Outgassing Hazards

A/C coil corrosion - Chinese Drywall - US CPSC

Details about Chinese drywall problems are at CHINESE DRYWALL HAZARDS. Excerpts are below. Photo at left showing air conditioner evaporator coil corrosion traced to Chinese drywall outgassing is provided by the U.S. CPSC.

Chinese drywall has received considerable attention in the U.S. as a source of odors, health hazards, and even corrosion of HVAC equipment, electrical wiring, and piping, found in North American homes renovated or built since 2001, and especially in homes built in 2006 and 2007.

The U.S. CPSC has received about 3,082 reports from residents in 37 states, the District of Columbia, American Samoa, and Puerto Rico who believe their health symptoms or the corrosion of certain metal components in their homes are related to problem drywall. State and local authorities have also received similar reports. - US CPSC.

Cracks in Interior Walls, Diagnosis & Repair

Most cracks on interior surfaces are cosmetic. They usually suggest incidental movement of the structure. In a few cases they suggest ongoing significant structural movement. If there is concern about structural movement, it is a good idea to take photographs of cracks with a reference point such as a ruler indicating crack size.

This is a great way to monitor cracks to determine whether there is enough structural movement to worry about. A series of dated photographs can be very useful to a specialist.

Patching Plaster or Drywall Damage - the Basics

Both plaster and drywall can be readily patched where small damaged areas are noted. Drywalling over old plaster or drywall is sometimes done where large areas are damaged. Localized repairs to any textured surface are usually noticeable because the texturing is difficult to match.

Cleaning and painting textured surfaces is more difficult than flat surfaces, and wallpapering over textured finishes is usually not possible. The strength and durability of textured surfaces is similar to plaster or drywall, although small projections are easily worn off the surfaces, if people or animals brush against the wall.

Loose Plaster Walls or Ceilings

Plaster lath board © Daniel Friedman


Large sections of walls or ceilings may become loose where plaster has lost many of its keys due to vibration and wear and tear.

Where there is danger of plaster falling, this should be corrected promptly so people won’t be hurt by falling plaster.

Details are at PLASTER, LOOSE FALL HAZARDS where we illustrate loose plaster and report a case of a catastrophic plaster ceiling collapse.

Sagging plaster ceilings (in our photo above and in Carson Dunlop Associates' sketches below, are traced to broken plaster keys - the protruding plaster that projected through the original plaster wood or metal lath and formed a "key" that held the plaster in place.

There are more than one causes of broken plaster keys, including a history of building leaks that soften the plaster or add weight causing it to loosen or even fall, building framing movement that breaks plaster keys, and "creep" in wood walls due to framing shrinkage or settlement.

Broken plaster wall keys lead to bulging (C) Carson Dunlop Associates Broken plaster wall keys lead to bulging (C) Carson Dunlop Associates

Mold on Interior Wall Surfaces

Recent media attention to possible health hazards from indoor mold has encouraged building occupants, owners, and inspectors to include a visual check for mold problems when examining a building interior.

white mold on pine paneling is hard to see unless illuminaged correctly white mold on pine paneling is hard to see unless illuminaged correctly

Actually a competent inspection for mold contamination begins outside, and includes the entire structure. That's because a thorough inspection for the history of building leaks or moisture problems, or building conditions or features that make water or moisture problems likely in certain areas can significantly aid in an assessment of the chances that there is a hidden mold problem beyond what's visible.

Our photos [below] demonstrate how the angle at which light is aimed at a surface can make mold invisible (above left) or obvious (above right). Details are at USING LIGHT TO FIND MOLD where we provide a detailed example and procedures for using lighting to find mold on surfaces.

Nail Pops in Drywall: Causes, Prevention, Cure

Open drywall nail pop © Daniel Friedman

Nail pops in drywall walls or ceilings are usually a minor cosmetic issue that is common in new construction.

As wood studs shrink, nail heads ‘pop’ out from the drywall surface, causing a bump or the blemish on the wall or ceiling.

This usually happens only on new work, and only one time. Repairs are straightforward.

Below we illustrate nail pops in drywall. At below left are typical closed nail pops associated with normal wood and material shrinkage - this in a home built in the 1970's.

Details about the causes & repairs for drywall nail popping are at DRYWALL NAIL POPS.

Drywall Cracks & Ceiling Nail Pops caused by roof truss uplift

Nail pops found in some building ceilings and actual tears or cracks at the wall/ceiling juncture at building walls located under the center of certain roof trusses when moisture & temperature differences between the truss bottom chord and upper members cause the truss to arch. Details of the roof truss uplift problem are at TRUSS UPLIFT, ROOF

Also see CEILING FINISHES INTERIOR and see Best Interior Finish Practices and see Q&A on Building Interiors: Leaks, Stains, Damage, Repairs and see FLOOR DAMAGE DIAGNOSIS and CEILINGS & WALLS, PLASTER TYPES.

More Reading

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Frequently Asked Questions (FAQs) about interior wall finishes

Question: The plaster (or drywall) on a shared condo wall is up to 1mm wide and goes from floor to ceiling on two floors. They reappear if patched

I am a woman who lives alone and im extremely worried that I might have subsidence in my house. I have been reading through you very helpful site for some time. However I would very much appreciate if you could offer a little advice. The house I live in is around 30 years old. The main problems appears in the plaster of an interior wall that is joined to my neighbor.

The plaster on my side of the shared wall is cracked in the bedroom upstairs from floor to ceiling and then downstairs there is another floor to ceiling crack in the plaster ( I do not know if the crack goes deeper as the wall is shared) . if in our I imagination the bedroom floor was removed the cracks would not run vertical from roof to ground. However they are in a 10 foot proximity. The cracks are staggered but do not follow a brick pattern. They are also a uniform width of between approximately 1/2 to 1 mm wide. The upstairs crack appears "deeper" than the downstairs crack.

In the opposite side of the house there is also a crack upstairs in the plaster that runs vertically from ceiling toward a window , The crack at its worst is no more than 2 mm wide at the ceiling and tapers into a hairline before it reaches the window. Again I cannot check if the crack has also appeared outside as it is by the roof and I do not have ladders or anyone to help me to gain access to view.

I know that the house is built on a clay foundation. There are also very large trees that are council owned at the end of the garden on public land. The trees are more than 15 meters away from the house but the trees are so large that the garden is in their shadow, which makes me think that the roots might also be very large and perhaps under the house.

I have spoken to my neighbor to see if she has any cracking, but on her side of the shared wall she has wallpaper and therefore she is not prepared to do anything to see.

I do not know if the cracks have "suddenly appeared". It is only when I came to decorate (paint) that I noticed them. A friend (none professional) scratched out some plaster with a knife and then filled with a none flexible filler (shared wall rooms only). The cracks reappeared within a month.

The cracks have been there for around 12 months (I think) and do not appear to have gotten any bigger (I think)

It is only since I have been reading about subsidence that I have frightened myself !

I do not really have the money to invest in a structural engineers unless absolutely necessary.

I am insured but frightened to approach my insurance as I know that as soon as you mention cracking the premium goes up and the value of the house goes down.

Any advice would be really appreciated. - A.C.

Reply: No panic, but some further evaluation of interior wall cracks is appropriate

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem. That said, here are some things to consider:

  • #1 don't panic so much that an opportunist takes advantage of your worry to do something costly that may be unnecessary, inappropriate, ineffective
  • The cracks you describe do not sound normal because of their extent, location, presence on opposite walls in the home. Therefore they are worth investigating.
  • The 1mm wide cracks themselves do not describe a large movement, though of course there may be more serious hidden conditions. But a vertical 1 mm crack in drywall alone is unlikely to be enough movement to alone threaten an immediate catastrophe. The fact that upstairs the cracks appear "deeper" than downstairs (perhaps wider too) is consistent with building movement or settlement that originates low in the structure, perhaps on the footing or foundation, since movement, as it is telegraphed to upper levels of the building, often results in cracks being wider as we look higher up from the point of origin.
  • Cracks in the common wall between two adjoining town home or condominium walls might be structural in import, but often those walls are not bearing the main roof loads and may be constructed principally as firewalls between two living units. Usually the common wall is a "gable-end" wall - it's the house front and rear walls that carry most roof and floor loads. (Though floor and roof loads in some designs are also carried by a beam that rests on posts in gable end walls. A firewall constructed of concrete block, when the rest of the structure was wood framing, might be a reason that those walls are behaving differently than the rest of the structure. (Other firewalls are wood-framed and covered with fire-rated drywall.)
  • Risks of foundation movement: In general the level of risk with foundation movement depends on the total amount of movement that has occurred, where it is, over what time it occurred, what is the underlying cause, and what are the effects on the structure. Significant amounts of movement or things found way out of level and plumb are of course a bigger concern as are signs that movement is ongoing, increasing, or rapid.
  • Onsite inspection needed: I'd be a fool to pretend to diagnose building cracks by email, not to mention sight unseen. You would do well to have someone with experience with building movement, structural questions, and foundation inspection take a look. Beware: a structural engineer who is not really familiar with foundations or residential construction may have great credentials but may give crazy and expensive advice that is safe for her but expensive for you. So before hiring anyone ask what is their experience with building cracks and movement. You could call a home inspector who has experience, a foundation repair contractor, even a general building contractor, as a starting point.
  • If your home has an unfinished basement or crawl space where the foundations and floor framing of the first floor are visible, it ought to be possible to arrive at a reasonably confident explanation of what's going on by studying the condition of the foundation and footing and by looking for evidence of rot or insect damage at the bottom of the wood-framed walls (if that's what you've got.) An inspector who does not look into such an area is not doing her/his job.

You might ask your insurance company to take a look, as they may do so without charging you. Of course their "expert" may not be one, and the company will certainly exclude certain types of building problems that they assert fall outside the scope of coverage of your insurance policy.

Our FOUNDATION CRACKS & DAMAGE GUIDE includes advice about type, location, pattern, size, activity, cause, and repair of types of building cracks that might be helpful. But in general, following a closer inspection of your home and those cracks, if the inspector's explanation doesn't make sense to you let me know what you were told and I can suggest some follow-up questions. And don't do anything expensive before you understand what's going on.


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