Chimney, Fireplace and Masonry Glossary

This is a masonry glossary of terms used for chimney repairs, chimney inspections, chimney restorations and fireplaces.

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Anchors are straps of steel secured into the bond beam and are tied back to the floor joist, roof rafters or wall members. The anchors tie the chimney to the house which may provide support in the event of wind or earthquake.

Anchored Veneer

Anchored means fastened to the structure so that it can not fall off.

Anchoring Ties

A device such as a metal rod, wire, or strap used to attach one object (such as a layer of brick) to another object (such as the structure).

Ash Mortar

In Los Angeles up until around 1939 Ash Mortar consisted of sand, lime and ash.


An attic is an enclosed area above the ceiling level in most residential homes that is designed as part of the roof system. The chimney systems often run through attic areas prior to exiting the roof exterior. NOTE: It is often the case that chimneys or flue systems can be damaged in this enclosed area. It is of paramount importance that all accessible attics be inspected around the chimney for any signs of structural damage, smoke or heat damage.

Ash Dump

The ash dump has a trap door on the floor of the inner hearth that leads to the ash pit.

Ash Pit

The ash pit is the space to dump ashes. It is a non-combustible storage compartment behind or below the firebox, which helps keep the fireplace clean without having to carry ashes through the house. NOTE: This door is found on the exterior of the chimney usually just above the dirt level.


A baffle as it applies to a chimney is a separation between two r more neighboring flue systems. This separation is designed to consolidate exhaust and not allow it to downdraft into neighboring flue systems.


A short pillar forming part of a series supporting a rail.


An entire railing system (as along the edge of a balcony) including a top rail and its balusters, and sometimes a bottom rail.

Barrel Ceiling

Barrel or Vaulted ceiling are design features in a home that raise the ceiling above the standard horizontal plane. This affect the inspection of a chimney because it usually minimizes the attic space above a normal ceiling height and may not allow an inspector to view any portion of the chimney in this area. NOTE: Standard chimney inspection is defined as a Level 2 inspection – this states that an inspector will inspect every part of the chimney that is ACCESSIBLE without having to damage the structure.

Black Paper

Stiff paper treated with a petroleum product to make the paper able to resist water. The paper is usually black so the construction industry has named it simply "black paper". Black paper is what is usually used under the stucco or bricks to ensure water that soaks through the stucco or bricks does not enter the building. It is only water resistant because on a vertical surface the water does not spend much time against the paper (as it is running down the wall) so it does not have a chance to soak in.

Bond Beam

A continuous beam (or thickness) usually constructed of concrete and reinforced with steel rods on top of supporting walls. The purpose of the bond beam is to tie the walls together and distribute weight evenly to the walls below.

For a Masonry chimney a bond beam is a member poured at the support level of the chimney. The support level is usually at the floor and at the ceiling or roof line. It may also be above the roof line if the chimney is tall enough to require a supplementary support. The bond beam acts as an anchor at certain levels of a masonry chimney.

Another application of the bond bean is to attach two dissimilar materials (see picture below). This particular form is constructed to attach a lower masonry chimney to a new metal flue. This is the Class A method of repair (also known as a “high temp flue system”) commonly used to repair chimneys suffering from earthquake damage. In L.A. county this is commonly referred to as an LA City Detail repair.

Breast Plate

The angled shelf above the interior firebox that directs exhaust to the flue system. Note: When this area is not angled properly and runs on a horizontal plane it can slow the fireplace’s ability to exhaust properly. Smoke can hit the horizontal shelf and roll out into the living area.

Carbon Monoxide

a byproduct of combustion. Primarily found in gas burning appliances more so than wood burning appliances, although wood burning are lower than gas burning due to the fact that wood burning fireplaces also exhaust smoke which is a warning indicator of poor drafting Carbon monoxide itself is an odorless, colorless gas that is an inherent health hazard, if natural gas burning appliances are not drafting properly carbon monoxide can build up and cause illness and/or death. During inspections it must be understood that this is a very real and present danger.


A continuous enclosure in a building that acts as a housing for such things as pipe, wiring (as in a chimney), or heating ducts. When you look at a house and you see the chimney sticking up past the roof you are looking at a chase unless the chimney is made of solid masonry. If it is solid masonry we call it the "stack".

Chase Cover

A flashing detail that is set at the top of an enclosed framed chase that is designed to not allow water or other environmental elements to enter chase system. During chimney inspections these chase covers have certain mechanical requirements; often they are required to allow for chase venting and clearance from combustible materials depending on the flue system that they are enclosing.


A Chimney is a shaft built to carry off smoke and the products of combustion that extends from the top of the throat to the top of the chimney.

Chimney Cap

Cap surrounding the top of the chimney brick and protects the masonry from the elements.

Chimney Chase

Chimney Chase is a chase encasing a pipe (flue) that exhausts the excess heat, and noxious gases from the fireplace below.

Chimney Crown

Chimneys should always be designed with a sloping crown to prevent water from running down next to the flue lining and into the fireplace. The chimney crown also prohibits the water from standing at the top and creating frost or moisture problems. The chimney crown prevents the brick and masonry of the chimney from becoming soaked from the top down. The chimney flue liners should project approximately two inches to four inches above the highest point of the chimney crown.

Chimney Shroud

The shroud is a hooded covering that is often used as a design detail over flue systems. These details can interrupt the ability of the flue system to draw properly. Example: if you put your hand over the top of an exhaust it would slow the ability of the exhaust system. During inspection these have to be looked at carefully to see how they may interrupt proper function of the flue system.

Chimney Top or Chimney Pot

A chimney top is a clay, concrete or metal extension to the flue that adds height and provides a decorative top to the chimney. NOTE: This is a designer detail and has to be inspected thoroughly in the same way as a shroud detail to determine if it is affecting the proper draw of the flue system. Often these pots or extension tubes downsize the flue system and can choke off its ability to draw.

Chimney Stack

The term Chimney Stack is used when a masonry chimney has a lining (clay flue).


A term used to indicate approximate date, in our case referencing when a house was originally built. Example: This house was built circa 1936. Circa would be approximately 1936.

Class A flue

A high temperature flue system used in repairing masonry fireplaces to replace existing or damaged masonry flues. It utilizes a bond beam to connect the lower masonry structure to the new metal flue system. The advantage to the flue system is that it is lightweight in nature and in earthquake prone areas it is commonly used to alleviate concerns due to the weight of masonry chimneys. NOTE: New structures can utilize this system with a new lower masonry firebox as well.


CMU stands for Concrete Masonry Unit. Also called concrete block, cement block, and foundation block.

Code Height

Refers to chimney height above the roof line. This is specified under code to ensure that the flue system will be allowed to draft properly. The standard rule of thumb is referred to as the 10 and 2 rule, meaning as the flue system exhausts to atmosphere it must be 2 feet higher than any portion of the structure within 10 feet of it. This is measured on a horizontal plane.

Copper Flashings

Flashings made from the metal copper. Copper flashings are superior because they will never rust or rot away. In time the copper takes on a patina giving it an attractive look.


A layer (or course) of bricks or other type of masonry units that protrude out from the layer (or course) below. The purpose of the corbelling is usually decorative although it is commonly used to form a ledge to support something.

Crawl Space

This is a term used to describe the area below floor level and dirt grade. It is usually accessible via a crawl space cover located somewhere on the exterior of the property wall or through the interior basement. During a chimney inspection it is important to locate this area and examine the chimney structure within. The inspector is obligated to look for any structural damage to the chimney in this area, i.e. broken bricks, condition of the hearth extension support, displacement and or any other signs of damage that should be noted.


A build-up of heavy particles usually from wood burning that stuck to the inside of the flue system, this coating is primarily made up of un-burnt material and resin from the wood itself. As this material build up it creates an uneven jagged surface inside the flue system that can be a fire hazard and also lowers the flue systems ability to draw exhaust. During inspections the buildup of this material needs to be noted and recommendations for its removal should be given, this is usually done by sweeping the chimney.


A structure usually made of sheet metal, placed behind another structure (such as a chimney) that protrudes up through the roof. The purpose is to divert water to each side of the protruding structure. The cricket prevents water from sitting directly behind the protruding structure.


A damper is usually a metal plate designed to cut off the air flow through the chimney’s flue system. Its primary purpose is to reduce heat loss from the interior of the home. Fireplaces without dampers allow the warm are in the house to directly vent up through the flue system. Energy can be conserved by proper installation of a damper system. Damper systems are not code required but are strongly advised for this reason.

NOTE: The building code requires that damper be removed or disabled so they cannot be closed in gas only burning fireplaces. Gas burning fireplaces primary exhaust is carbon monoxide. Carbon Monoxide builds up in the house undetected. To insure proper venting is taking place at all times, and for the health and safety of the people living in the house, dampers must not exist in gas only burning fireplaces.

Dampers – Top Mounted

Top mounted Dampers are an alternate damper system. This system is placed at the very top of the flue inside the spark arrestor. Other forms of dampers do exist but are rarely found.

Design Detail

This refers to a designer modification for aesthetic purposes.


A term used when a structure shows signs of shifting from its original placement.

Dog Leg Crack

A descriptive term for a break in a structure primarily in brick or concrete block that transfers in a vertical-horizontal pattern. This cracking usually follows the mortar joint between masonry units such as brick or concrete block.


In fireplace layman's terms, drafting means the same as draw, which is how well the system takes the products of combustion from the fireplace up through the chimney to the outside. If a fireplace does not draft well, or draw well, you would get smoke in the room. The smoke would come out of the fireplace opening.

Drafting Ratios

A drafting ratio is the size of the fireplace opening compared to the size of the flue. In order for a fireplace and chimney system to draft or draw well this size relation has to be correct. For example, if the fireplace was very big and the flue was small, the system would allow smoke to enter in the room.

Draft Stop:

A barrier wall designed to minimize air flow that is set on a vertical plane, this is to consolidate the amount of air that can be pulled into an area that is on fire. The reasoning behind a draft stop is to not allow the acceleration of fire into adjoining enclosed areas such as attics.

Encircling Crack

A term used to describe damage to a structure, i.e. cracking that transfers all the way around the structure itself. This can usually be found on areas of exterior or interior flues and indicates that the chimney is broken.


Comes to us from chemistry, and means loss of water from crystal. When a crystalline substance loses water a deposit is left and this process and the actual deposit is called efflorescence. It is harmless and is formed from a mineral which is basically a water soluble salt. It will wash away with special detergents and will stop appearing once the source of water is removed.

Exhaust Fan

An exhaust fan is a mechanical fan that increases the draft through the flue and prevents smoking and back-drafts. These are installed in flue systems due to the lack of proper drafting. Reasons for installation may include undersized flue or home built on a hillside where wind conditions can cause downdrafts into the flue system.


The non-combustible material such as brick, tile or stone that directly surrounds the firebox opening. The building code has minimum standards required for facing materials as far as depth and distance from combustible materials.

Fire Box

The firebox is the chamber or area where the fire is built. It is generally built with fire brick laid with thin joints. The side walls are slanted slightly to radiate heat into the room. The rear wall is sloped or curved to provide an upward draft.

Fire Brick

Fire brick is a hard-fired refractory brick that may line a firebox and is able to resist the heat of a fire. A fireplace lined with fire brick will help reduce maintenance of the firebox. Refractory refers to something that reflects heat, in this case instead of absorbing heat it reflects it.

Firebox Brick Patterns

Fire Chamber

See Fire Box

Fire Guard

A high tech cement like chemical compound that is not adversely affected by high temperatures and has a tremendous ability to stick to other masonry surfaces. Used inside of chimneys to seal cracks and to coat concrete that is adversely affected by high temperatures.

Fireplace Hood

A hood is an ornamental fixture of masonry or metal that is sometimes placed in front of and above the fireplace openings. Hoods must be made from a non-combustible material.

Fireplace Opening

It is the opening of the fireplace into the firebox itself.


Sometimes called a draftstop. A horizontal barrier that is set between floors at ceiling and floor level to consolidate airflow so as not to allow it to accelerate into adjacent areas such as second floor and/or attics. Standarly firestops are made from non-combustible materials such as sheet metal if they are going to come in contact with flue systems. Today’s building code requires a standard clearance of 2 inches from any flue system or chimney structure to any combustible material.


A thin impervious material (such as metal) placed in construction (e.g., in mortar joints and through air spaces in masonry) to prevent water penetration and/or provide water drainage, esp. between a roof and wall, and over exterior door openings and windows. The copper seen in the photo below is the flashing. In the photo below the flashing prevents water from entering the building between the chimney and the roof.

Floor Joist

Underneath the flooring there are supporting members that hold the floor up, those are called floor joists. If they are in the ceiling they are are called ceiling joists.


Smoke and combustion gases from a fireplace fire pass up the chimney inside the flue. Each fireplace should have an independent flue, entirely free from other openings or connections. A flue may be lined or unlined. An unlined chimney flue should be larger than a lined chimney flue, the reason for this is that a lined chimney flue system has a smooth interior wall and unlined chimney flue systems are built with bricks that are uneven in shape. The uneven surface slows the ability of the unlined chimney flue system to exhaust the products of combustion. The increased size of the unlined chimney flue gives more area for the exhaust to escape. The shape of the flue system has to be taken into consideration. Round flues exhaust better than rectangular flues. The size of the flue and the height of the chimney above the roof are important to create the proper draft through the fireplace and to ensure adequate burning of fuel and the passage of smoke.

Flue Systems Designs

The common systems for flue design are oval clay or pumice, rectangular clay or pumice and Double Wydth brick, and single width brick.

  • Oval clay flue liner is a Terra cotta clay tube like section used to build interior flue varying in size. These are most commonly used after 1938 and can indicate that steel reinforcement is used in the chimney, but not necessarily.
  • Rectangular clay liner is Terra cotta clay tube like section used to build interior flue varying in size. These were primarily used prior to 1938, between 1928 and 1938 and may indicate non-reinforced clay lined chimney structure, but not necessarily.
  • Double Wydth is a flue design where 2 bricks equaling 8 inches in thickness are used to build chimney flue interior. This is required because without the Terra cotta clay, flue code mandates that the flue must be a minimum of 8 inches in thickness rather than 4. This design is not date specific and would not be a good indication of when the chimney was built as it is still in use and was in use during the 1920’s.
  • Single Wydth is a brick chimney design. Most chimneys build with this design are from 1928 and earlier. The mortar used in this system is referred to as ash or lime mortar and is very weak in nature. These flue systems and chimneys are inherently the most susceptible to damage during seismic activities and are also most commonly found to suffer structural damage due to age and erosion.


Footing is the anchor at ground level for the chimney structure itself. It is standardly embedded into the earth and acts as a base for the chimney. The steel reinforcement is set below grade and is encased in concrete.


This is also referred to as a footing. The foundation of a chimney is usually made of masonry or poured concrete designed to support the weight of the chimney, resist frost action on the structure or any additional load imposed and to prevent the settling or tipping of the chimney.

Gas Log

A gas log is a self-contained, free-standing, open flame, gas burning appliance consisting of a metal frame or base supporting simulated logs and designed for installation only in a vented fireplace.


Grade is the level in which earth meets exterior structure. Ex: When you are looking at a house grade is where the house wall meets the earth. Footings are set below grade meaning they are below the level where the house meets the ground.


The hearth is the interior floor of the firebox. The inner hearth may be made of fire-resistant bricks and holds the burning logs; the outer hearth (also known as the hearth extension) may be made of brick, tile or other non-combustible material. It is supported on concrete or may be part of the concrete slab foundation.

Hearth Extension

The exterior, non-combustible area around the firebox opening is the hearth extension. This is designed as a safety zone outside the fireplace to protect from burning material getting onto the floor as well as a safety area so people do not walk too close to the fireplace opening.

High Temperature Paint

This is a paint that is used on interior fireboxes to disguise or change the color of interior brick and it is approved for use on surfaces that reach temps that reach 1,200 degrees. This is also used on spark arrestors and other metal components that are exposed to heat.

Isokern or Firerock

Modular masonry fireplace and chimney systems made from volcanic pumice stone used for indoor, outdoor, multifamily and commercial projects.


A horizontal support member running from support to support that holds up the floor or ceiling.

Level I Inspection

Home Inspectors, as thorough and as diligent as they are, perform what is known as a Level I Chimney Inspection when inspecting a home. To avoid undue technical jargon, a Level I Inspection is a cursory inspection of the chimney using only the naked eye. Are there any major signs of damage?, etc.

Level I I Inspection

Of course a Level II inspection includes all aspects of a Level I inspection with the following points added:

  1. Has the chimney been constructed properly?
  2. All accessible portions of the chimney are inspected including all enclosed flues.
  3. Does the chimney show proper clearance from combustibles in accessible locations?
  4. All accessible portions of the chimney exterior and interior are inspected including areas with accessible attics, crawl spaces and basements.
  5. Shall include video scanning or other means of inspection.

Level I I I Inspection

All aspects of the Level I Inspection and Level I I Inspection. Proper construction condition of concealed portions of the chimney structure and enclosed flues. Also the proper clearance from combustibles. It includes external and internal portions of the chimney structure, including concealed areas of the building or chimney. It includes removal of components of the building or chimney when necessary. Removal of such components shall be required only as necessary to gain access to ares that are the subject of the inspection.


See Flue


The lintel is standardly a steel support that holds up the masonry opening of the firebox. This is installed to support the masonry because otherwise it would have no support structure. On an arched firebox opening this would not be installed because the arched design is self-supporting.

Load Bearing

Capable of supporting a load in addition to its own weight.

Mantel Shelf

A mantel shelf is located above the fireplace opening, it serves as a decorative device to hold ornaments. The mantel may be made of wood, masonry, marble or other materials. All decorative wood materials around fireplace openings must clear the opening itself by a minimum of 6 inches, this includes the sides and above the firebox opening. The six inch minimum clearance applies if the decorative wood details are flush with the masonry non-combustible firebox opening, if the wood details extended outwards then the clearance rule changes.


Anything having to do with brick, stone cement or mortar and their use as construction components.


A tar like substance that is used to seal water leaks primarily in roof details around chimney and other penetrations above roof. This material is usually patchwork repair and not considered a high end, long term solution.


Any essential part as a post or beam, etc., of a framed structure. A structural member is any one piece of the framework that actually carries a load or helps another piece carry a load. In the human body your thigh bone is a structural member.


A type of metal pipe used in pre-fabricated metal fireplaces. Names of other manufacturers of Class A flue pipe: Metal Fab & Duratech.

Modified Bituthene

A petroleum based product that looks and behaves like a sheet of rubber. Used to waterproof a wall when one really wants to ensure the wall does not leak.


A bonding agent used to join masonry units, this material has a sand and cement mixture specifically formulated to adhere to masonry units, i.e. brick or concrete block together.

Non Load Bearing

Only capable of supporting its own weight.


A term used to describe chimney built commonly before 1938 that do not have any structural steel reinforcement incorporated into them. Chimney inspectors try to determine if a chimney is reinforced or not reinforced because this can weigh heavily into how the chimney is damaged and can it be repaired. The date the house was built can be an indicator. The flue system design is also an important note.


A component used in a metal fireplace, made in the shape of an elbow that has varying degrees such as 30 degree or 45 degree. This offset is standardly no greater than 30 degrees under normal wood burning fireplace requirements. In gas only burning systems offsets may increase to 45 degrees under specific requirements.

Outside Air Intake

This is an energy conservation feature and is required for fireplaces located on an exterior wall. It is intended to reduce the amount of preheated room air used for combustion. Current Building Codes require the installation of glass doors on fireplaces, this does not allow air to be pulled from the living area and therefore makes it necessary to install an opening in the firebox that leads to the exterior from which to draw air.


A thin cement like coating placed on the interior of smoke chambers or flue systems to smooth their surface allowing for better drafting. Parging is also a term used to seal gaps and voids between clay liners.

Portland Cement

Portland cement is the most common type of cement in general usage, as it is a basic ingredient of today's concrete, mortar and plaster. The city sidewalks and curbs are one example of Portland Cement concrete. It consists of a mixture of oxides of calcium, silicon and aluminum. Portland cement and similar materials are made by heating limestone (as source of calcium) with clay or sand (as source of silicon) and grinding the product (clinker), with a source of sulfate (most commonly gypsum). The resulting powder, when mixed with water, will become a hydrated solid over time.

Portland cement was first manufactured in Britain in the early part of the 19th century, and its name is derived from its similarity to Portland Stone, a type of building stone that was quarried on the Isle of Portland in Dorset, England. The patent for Portland cement was issued to Joseph Aspdin, a British bricklayer, in 1824.

In terms of chimneys in Los Angeles, the use of Portland cement in mortar started after the 1933 Long Beach Earthquake when engineers realized that seismic activity demanded the powerful bonding strength of Portland cement. Since Los Angeles did not experience the freeze—thaw cycle of the colder climates there were no disadvantages of using Portland Cement in the brick mortar in Los Angeles and it is standard practice today.

Powder Coat

Powder coating is an advanced method of applying a decorative and protective finish to a wide range of materials. The powder used for the process is a mixture of finely ground particles of pigment (color) and resin, which is sprayed onto a surface to be coated. The charged powder particles adhere to the electrically grounded surfaces until heated and fused into a smooth coating in a curing oven. The result is a uniform, durable, high-quality and attractive finish.

Prefabricated Fireplaces

These are pre-engineered and factory built fireplaces and the flue systems usually consist of metal components of lightweight design. These units are UL listed and laboratory tested to be installed EXACTLY as the manufacturer dictates. All manufacturers have specific installation instructions and component parts. The lifespan of these units is usually between 15 to 25 years depending on usage and environment. During a chimney inspection of prefabricated fireplace systems certain guidelines can apply as far as inspection requirements but all prefabricated fireplaces must be installed per the manufacturers requirements and these do vary.

Products of Combustion

As fuel (wood or gas) burn they produce heat and other byproducts . The other byproducts are particles that have not completely burned such as ash, carbon monoxide and creosote.

Push Pull Test

It is a test used to assist the inspector in determining if the chimney structure has suffered damage. It is done by the gradual and consistent application of pressure and release of pressure to the chimney structure to see if the chimney will move to an excessive degree. This test is primarily used with masonry chimneys but can often come in handy with framed structures that are improperly secured to the main home structure.


A right angle stone in the corner of a masonry wall to tie in or strengthen the wall. Seen in the corner and is usually distinguished decoratively from adjacent masonry. Original purpose was to reinforce an external corner or edge of a wall but today quoins are mostly decorative in nature and have no structural factors, being made mostly of either light weight precast concrete or expanded foam.

Rain Caps

Some chimneys for heating systems, and for fireplaces, are equipped with rain caps to keep rain water from entering the chimney flue. Look for a flat or curved plate at the very top of the chimney. The rain cap can be viewed from the ground.

It is important for the home owner to periodically verify the integrity of the rain cap, especially after heavy rains and winds because weakened rain caps can often fail under these conditions. If a rain cap becomes dislodged, rain water can enter the flue and then run down into the heating system, or fireplace, and cause damage or system malfunction.


See Fire Brick


A description of a masonry chimney structure that has internal steel reinforcement built into it. This reinforcement is designed to strengthen structure and primarily keep it from breaking and falling over. California building Code requires this because we are in an earthquake zone.

Roof Brace

This is an angular brace that is set above the roof line adjoining the chimney to the roof. Its purpose is to keep the chimney from moving excessively under movement such as an earthquake. The size and design of the brace vary due to the height of the chimney off the roof line.

Roof Pitch

This is a term used to describe the angle of the roof beyond a horizontal plane. It is determined by measuring from the roof horizontally 12 feet out and then drawing a line vertically to where the roof intersects with that 12 foot mark. The distance from the top of your 12 foot mark to the point where it connects to the roof is the pitch. EXAMPLE: 12/3 pitch would mean 3 feet down from the 12 foot mark is where you contact the roof line. The following illustration is supplied courtesy of Northern Virginia Gutter Cleaning

Smoke Chamber

The transition zone between a fireplace throat and fireplace chimney, extending from the damper or throat to the base of the first flue. The smoke chamber acts as a funnel to compress the smoke and gases from the fire so that they will squeeze into the chimney flue above. The smoke chamber is important for good draft action. It should be symmetrical in shape so that the draft pulls evenly on the fire in the firebox. A symmetrical smoke chamber prevents fire from burning on one side of the firebox, causing uneven flame distribution. The smoke chamber should be centered with the flue directly above the fireplace and its walls should be sloped at the same angle to provide even draft from the firebox to the chimney. NOTE: The smoke chamber is standardly triangular in shape and the interior walls should not deflect more than 30 degrees from vertical in its design. This is due to the fact that great defection can slow the flue systems ability to draw. Also interior smoke chamber should not exceed the area o interior of firebox in volume. This is due to the fact that the smoke chamber needs to be able to compress exhaust properly and if it is too large it will not achieve the desired effect.

Smoke Shelf

The ledge directly behind the throat of the fireplace, at the base of the smoke chamber.



A brand name for a cardboard pipe. The purpose of a cardboard pipe is to form round columns of concrete. One will pour concrete in the pipe and after the concrete has set — remove or cut away the cardboard pipe leaving the round concrete column. This cardboard pipe is treated so the concrete will not stick to it. Boston Brick & Stone uses Sonotubes to form round holes inside of solid concrete.


This indicates the flaking or erosion that occurs to brick or stone due to heat and moisture and occurs over an extended period of time commonly seen on the interior of a firebox.

Spark Arrestor

A noncombustible screen installed between the top of the chimney and the underside of the chimney cap; prevents the escape of sparks and burning materials from the chimney. this is made from wire mesh, the holes in the wire mesh are required to be between 3/8 and 1/2 inch in size. NOTE: Code dictates that the area of the screen in a spark arrestor is four times the cross section of the interior of the flue. Example: If the cross section of the flue is 100 inches the area of the spark arrestor would be 400 inches, this is the standard calculation. The reasoning behind this is to allow for the buildup of debris on the spark arrestor over time and still adequately draft the flue system.

Stainless Steel Liner

A lining system used to correct damage to existing flue systems.

Structural Members

Structural means having to do with support, in other words "holding something up. The skeleton provides the structural support for the human body. In a house the 2 x 4 wooded studs and beams provide the structural support thus are structural members. In a skyscraper the steel or concrete framework provides structural support and in all cases the structural support is what keeps the structure from falling to the ground.


The narrow passage above the fire chamber of a fireplace, forward of the smoke shelf and below the smoke chamber, generally has a damper which must be opened before the fireplace is used, and may be closed, when the fireplace is not in use.

Note: Dampers used with fireplaces that burn gas only must, by code, be in the locked-open position at all times.

Throat Mounted Damper

A damper located in the throat of a chimney.


Is a term used to repair cracking between masonry units at mortar joints, this is considered a cosmetic repair but doe assist in keeping water from penetrating into cracks in masonry structures and extend their life. This is done by grinding out the mortar joint to a depth of 3/4 to 1 inch and then tucking mortar back into the joint.

UL Listing

This is a common term for a product that has undergone laboratory testing under functional conditions and approved by said laboratory for installation per manufacturer’s instructions. Underwriter is one of several that perform this function, UL stands for it being tested by Underwriter laboratories.


A thin layer of brick or stone placed over a wooden or steel shell to mimic an appearance of full brick or stone work. This is done for 2 reasons, one to minimize cost in some circumstances and Two to minimize weight.


Masonry terminology referring to the size of the brick.

Wythe (or withe)

Each continuous vertical section of wall, one masonry unit in thickness.


Any system of bracing (bracing here means used to add strength) in which pieces of the framework are set to cross diagonally. When they intersect this way they form an "X". This system makes a very strong structure.