Spalling occurs when hydrostatic pressure builds up behind a brick wall, allowing too much moisture permeance. The water is absorbed into the brick and, because of variations in temperature and pressure, the water expands. This expansion can causing flaking, cracking, or even bricks that become split entirely.

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Frog and lack of frog in Capitol Hill Brick until 15th St NE

The vast majority of the buildings in the historic parts of Capitol Hill are built with “frog-less” bricks.

It is said that the slop molds which were once used to create bricks in the mold making process, with an indentation set in, look like a frog with its legs at its side and its torso in the middle of the box.  There may be no documentation to confirm the original use invention of this method of molding bricks, however this explanation of the etymology seems plausible.

Brick with a frog, rarely found in historic Capitol Hill.

The frog is an indented cast, molded or formed into the bottom of a masonry unit. A brick created with a frog has several advantages. It is a more stable method of setting the brick into the mortar bed. That three-dimensional shape that’s left by the frog adds stability because it provides a key for the mortar to fill and lock the brick in laterally.   The presence of the frog also allows a brick of the same size to be shipped or transported and used in construction at a lower weight, which saves fuel cost and reduces labor for installation and construction.

Later, after frogs were first used in brick production, each brick manufacturer began putting their name into the frog. This gave the brick manufacturer an opportunity to do a little bit of marketing and the letters in the name also added yet a more three-dimensional surface to which the mortar could embed.

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Bat Closer

A Bat Brick is a brick cut across the width, shortening the length of the brick.  A brick cut to 3/4 the length is a 3/4-bat; similarly, a brick cut in half is a half-bat. A Bat Closer is used at the end of the brick course to end the row but still make a flat surface.  Brick courses are typically laid offset from the one below, which forms a stronger bond than if the mortar joints simply ran in long rows and columns across an entire wall. If you only used whole bricks in offset courses, the corner of your house would have bricks jutting from the side in every other course. A bat closer is used to finish a course and make it flush with the one below it.

A half bat closer is used on the left side of the surface shown, at every other course.

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Brick Corbelling

Brick corbelling is a pattern that sets subsequent courses extending out from the planar surface of a wall. The technique allows the lower courses to support the courses above which jut further out, though typically it is constructed for purely aesthetic reasons. Around Capitol Hill, corbelling is typically seen at the tops of row homes, usually with some variation that adds to the décor.

The following picture is an example of dental corbelling on Capitol Hill.


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Lime mortar

During the construction of most Capitol Hill row homes at the turn of the 20th Century, modern strong mortar was not available to brick and stone masons. Our modern Portland cement has only been recently used for a short period of time for masonry construction (in America). Prior to portland cement, lime and sand were used as mortar. They set up to harden and were able to hold stone in place. While it is not required by the Building Code to use lime mortar when pointing historic brick, it is the best practice because the brick has a density of 800 to 1800 psi and has a higher level of permeability than modern brick.

If you use Portland or modern cement with historic brick, it will lead to hard points between the brick and cause cracking when the brick is exposed to naturally occurring thermal energy forces.

Additionally, there is moisture in the existing mortar joints. Modern commercially available or retail cement has less permeability than lime mortar, which will cause moisture to build up inside the wall and cause cracking, known as “spalling.”

This picture shows both the lime mortar and the flush mortar joint, which was typical of brick mortar here, when the historic buildings in Capitol Hill were constructed.

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Common Brick

Common brick was machine made but soft and potentially irregular. It is often used on the sides of row homes, while the front facade is composed of more uniform “pressed brick.”

In this picture, the plaster was actually removed from the majority of the brick surface.  At the turn of the last century, it was common to cover the wide and sloppily placed/grouted interior brick with plaster.

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Raked, flush, and concave joint

The picture below is a common brick with a flushed mortar joint, which is very common to the original construction here in Capitol Hill.

The following picture is a concave mortar joint which is very common to typical construction in tract homes in modern construction outside of the city. This particular picture is in Capitol Hill, but at a newly-renovated and rebuilt area of masonry for a commercial condo building, NOT historic construction.

The following pictures shows a raked joint and a modern concave joint side-by-side.

The mortar joint on the left is a modern concave joint and a raked joint in the right hand side. As a side note, any joints between planar masonry surfaces such as shown here should be filled with an elastomeric or similiar flexible sealant.

The following diagram shows an assortment of different styles of mortar joints. Each is struck in a different style.

A close up view of a raked joint.

Another example, this time of an entire wall section of raked joint

This photo shows an example of the the grapevine mortar joint.

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Lateral support

Lateral Support would aid a wall from shifting side to side, perpendicular to the path of the wall. Buttresses are an example of lateral support in brick masonry.

“Barnstars” are a commonly-used name for anchor plates. The anchor plates are installed with tie rods often back to floor joist and structural deck framing.

“Barnstars” on Common Brick Wall in Capitol Hill


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Common Bond

American Bond, or Common Bond, is a style of laying masonry which employs a header course every few stretcher courses. Unlike English Bond, in which the two courses are alternated, in this technique, the header course is typically only used every 5-8 courses.

This is one of the most typical types of brick construction in Capitol Hill. Notice, this is different than the running bond.

In this type of bond, the Heather Bond locks the double wythe of brick together.

The wall in this photo is built with brick in a Commodore American bond pattern. I noticed there are “Barnstars” installed for prevention of lateral deflection.

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