Material Conditions Series Part 19: Slate Conditions

April 14, 2015

Each week we’re bringing you an in-depth look at one of the standard conditions we encounter and document during inspections of buildings and civil structures. 

Part 19: Slate Conditions

Slate is a metamorphic rock that is easily split along its layers and dressed, yielding an attractive, durable roof tile. In the U.S. slate is quarried in Pennsylvania, Virginia, New York, Maine and Vermont. Natural color variations in slate – including gray, green, purple, and red – are often combined for architectural effect.

Cracked and missing slate

Cracked and missing slate

 

Slate conditions include failed fasteners; cracks; various types of soiling; and unsecured slate.

Loose slate resulting from a failed fastener

Loose slate resulting from a failed fastener

Slate roof tiles are generally very durable, with a well-designed slate roof having a service life of at least 60 years, and often 100 years or longer. Slates with greater amounts of impurities are subject to destructive weathering with wetting and thermal cycles. Weathered slates lose strength, becoming more prone to cracks. Steeply-pitched roofs shed water more efficiently, reducing weathering and resulting in substantially longer service life. Metal fasteners are prone to corrosion and eventual failure, leaving loose or unsecured slates. When only a few roofing slates are deteriorated, a roof that is in otherwise good condition can be easily repaired by a skilled roofer.

Failed fasteners and missing slates

Failed fasteners and missing slates

Next in this series: Stucco Conditions

Click here to see previous posts in this series.


Material Conditions Series Part 18: Wood Conditions

April 7, 2015

Each week we’re bringing you an in-depth look at one of the standard conditions we encounter and document during inspections of buildings and civil structures. 

Part 18: Wood Conditions

Wood is one of the oldest architectural materials. In historic and modern exterior applications, wood may be used in the form of structural timbers or dimensional lumber, roof and wall cladding or underlayment, carved or turned decoration, as a component in door and window assemblies, and in balustrades and railings.

Structural wood members exhibiting biological growth (algae) and rot

Structural wood members exhibiting biological growth (algae) and rot

Wood conditions include biological growth, which includes both lower plants (fungi, lichens, algae) and higher (vascular) plants; sound and failed coatings such as paint; cracking and checking; infestation by insects or mammals; abrasion, weathering, and rot; sealant failure; sound and failed patch repairs and dutchman repairs; various types of soiling; and unsecured wood due to failed fasteners.

Checked structural wood member

Checked structural wood member

As a plant-based material, wood is subject to some types of deterioration that do not affect other building components, such as rot and insect damage. Rot, which is a type of fungal attack, requires moisture and often occurs when wood elements aren’t adequately protected from the elements by paint coatings or weatherproofing details. Abrasion is wear on the surface of wood from foot traffic, handling, or contact with moving parts such as hardware. Weathering occurs due to exposure to wind-blown dusts, water and ultraviolet light, resulting in discoloration and/or surface loss. Often, the wood’s softer seasonal growth is lost at a greater rate than the denser seasonal growth, resulting in an uneven surface texture. Cracking occurs when wood yields to external stresses, often as a result of weakening by other forms of deterioration. Checking, on the other hand, is splitting along the wood grain caused by drying, and does not typically affect the strength of the wood.

Weathered wood louvers

Weathered wood louvers

Next in this series: Slate Conditions

Click here to see previous posts in this series.


Material Conditions Series Part 17: Metal Conditions

March 31, 2015

Each week we’re bringing you an in-depth look at one of the standard conditions we encounter and document during inspections of buildings and civil structures. 

Part 17: Metal Conditions

Metals used in the construction of buildings and civil structures include cast and wrought iron, steel, aluminum, copper, lead, zinc, tin, nickel, and various alloys. We document conditions for architectural metal (structural members, windows, spandrel panels, railings, sculpture and cast ornament, fasteners, etc.) and sheet metal (thin metal typically used as cladding for roofs and cupolas, flashing, and as ornament.)

Dented sheet metal grotesque

Dented sheet metal grotesque

Metal conditions include failed coatings; failed fasteners; corroded fasteners; prior repairs; various types of soiling; failed sealant; dented metal; and unsecured metal. We distinguish among three types of corrosion conditions: surface corrosion, pitted corrosion, and perforated corrosion. Some conditions affect only architectural metal: cracks, bent metal, failed flange connections and failed welds; and several conditions affect only sheet metals: failed folded seams, failed soldered seams, puncture damage and tearing.

Unsecured cast iron ornament

Unsecured cast iron ornament

Corrosion (and failure of fasteners through corrosion) is the principal mode of failure for architectural and sheet metals, especially iron and its alloys. Corrosion is accelerated when dissimilar metals are placed in contact with each other (galvanic corrosion). Corrosion of sheet metal roofing and cladding is accelerated by contact with atmospheric contaminants. When designed for exterior applications, cast and wrought iron were often protected with paint coatings. Loss of protective coatings (paint, plating, or galvanizing) leads to rapid corrosion of iron-based sheet metals. Some metals, such as copper and aluminum, are resistant to corrosion except by galvanic action. Sheet metals are also susceptible to impact damage, fatigue, and tearing.

See also: Pack Rust and Failed Coatings

Next in this series: Wood Conditions

Click here to see previous posts in this series.


Material Conditions Series Part 16: Plaster Conditions

March 24, 2015

Each week we’re bringing you an in-depth look at one of the standard conditions we encounter and document during inspections of buildings and civil structures. 

Part 16: Plaster Conditions

Plaster is a finish material used principally for interior walls and ceilings. Ubiquitous in buildings of all types until well into the 20th century, plaster’s low cost and ease of workability made it a natural choice for creating interior finishes ranging from simple to ornate. Historically, flat plaster was applied to walls and ceilings in two or three coats over a wood lath substrate. Decorative moldings, coffered ceilings, and ceiling medallions were either formed on-site or cast in molds. Plaster may have a variety of finish treatments, including surface textures, wallpapers and decorative painting, sometimes in imitation wood or stone.

Water-damaged plaster that has separated from the substrate

Water-damaged plaster that has separated from the substrate

We document failed coatings; cracks; sound and failed crack and patch repairs; failed lath; replacement repairs; water damage and water staining; and unsecured plaster.

Unsecured plaster medallion

Unsecured plaster medallion

Structural movement and vibrations from vehicle traffic or construction activity can cause plaster to crack, often at the corners of rooms or at the corners of windows and doors. Water staining is usually indicative of roof or plumbing leaks, which can eventually lead to significant deterioration and cracking, separation from the substrate, and failure. Substrate failure may occur due to rusting fasteners or other modes of deterioration. Plaster keys (the plaster that oozes between the lath, forming a mechanical bond) can be damaged or broken by inappropriate treatment – for example, a plaster ceiling in an exposed attic space may be carelessly walked on. Later building modifications, such as retrofitted mechanical systems and interior reconfigurations, often result in substantial damage to plaster walls and ceilings.

Next in this series: Metal Conditions

Click here to see previous posts in this series.


Material Conditions Series Part 15: Glass Conditions

March 17, 2015

Each week we’re bringing you an in-depth look at one of the standard conditions we encounter and document during inspections of buildings and civil structures. 

Part 15: Glass Conditions

Architectural uses of glass include window glazing, glass block, curtain wall panels, and even structural glass. Window glazing may include clear glass, stained glass, faceted or textured glass, and wire-reinforced glass.

Bulged glass panes in a multi-light window

Bulged glass panes in a multi-light window

Typical failure conditions in glass or window assemblies include cracks, putty failure, sealant failure, missing or unsecured glass, and bulging panes (found in multi-light window configurations held in place with metal came, such as stained glass and art glass).

Cracked, loose, and missing glass in a multi-light window

Cracked, loose, and missing glass in a multi-light window

Some components of glass window and curtain wall assemblies – putty and sealant – degrade over time and can be expected to need repair or replacement as part of regular maintenance. Glass itself is resistant to decay, so conditions like cracked or loose pieces of glass are usually caused by the failure of surrounding materials, impact forces, or weather events.

Putty failure in window glass

Putty failure in window glass

Next in this series: Plaster Conditions

Click here to see previous posts in this series.


Material Conditions Series Part 14: Previous Repairs

March 10, 2015

Each week we’re bringing you an in-depth look at one of the standard conditions we encounter and document during inspections of buildings and civil structures. 

Part 14: Previous Repairs

Previous repairs are prior attempts to remedy building material failures. We typically categorize repairs as crack repairs, patches, dutchmen, or replacements, and we distinguish between sound repairs and failed repairs. Failed repairs may be due to inappropriate repair materials or poor installation, or they may indicate ongoing problems such as water infiltration, thermal movement, etc.

Sound crack repair in a precast concrete panel

Sound crack repair in a precast concrete panel

Repairs can be made with a wide variety of materials. Repairs to masonry may include cementitious mortars and patches, epoxies, replacement of units or portions of units with in-kind materials, or replacement with composite materials such as glass fiber reinforced concrete. Metal repairs may be soldered, welded or attached mechanically. Stucco and plaster repairs are usually made in-kind, however plaster moldings and other decorative details are sometimes cast with composite materials. Repairs to wood typically include dutchmen, epoxies, or replacement of entire members with new wood or with composite materials.

Replacement repair in brick

Replacement repair in brick

Documenting both failed and sound repairs can reveal underlying causes of deterioration and chronic problem areas, and can provide information about how a structure has been maintained over time.

Failed dutchman repair in limestone

Failed dutchman repair in limestone

Sound patch repair in sheet metal

Sound patch repair in sheet metal

Next in this series: Glass Conditions

Click here to see previous posts in this series.


Material Conditions Series Part 13: Failed Coatings

March 3, 2015

Each week we’re bringing you an in-depth look at one of the standard conditions we encounter and document during inspections of buildings and civil structures. 

Part 13: Failed Coatings

Failed coatings include paints, sealants, and other surface treatments that exhibit blistering, peeling, wrinkling, crazing, checking, alligatoring, chalking, staining, discoloration, pinholes or other types of deterioration.

Failed paint coating on wood

Failed paint coating on wood

Coating failure – especially paint failure – has numerous causes. These can include: poor surface preparation, weathering, use of inappropriate or incompatible treatments, poor bonding between layers of coatings, ultraviolet degradation, atmospheric or biological soiling, improper application, and more. Coating failure can be both a symptom and a cause of deterioration.

Failed paint coating on sheet metal

Failed paint coating on sheet metal

Next in this series: Previous Repairs

Click here to see previous posts in this series.

 


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