Weak Mortar

Over the holidays my family experienced a masonry disaster.  The culprit: weak mortar.  A bit of chaos ensued, but fortunately there was a conservator in the house to help stabilize the situation.

You see, on Christmas Eve my sister and her kids made a gingerbread house.  My niece and nephew had a great time decorating their gingerbread house with candy and frosting.  Their house looked beautiful!  And they were so proud of their creation.

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Following the obligatory photo shoot, the adults retired to the living room when suddenly there was a crash!

And a scream!

And two sad little whimpers.  (Followed by giggles, naturally.)

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The gingerbread house had collapsed!!! (Dun dun dun)

Fortunately, an architectural conservator who specializes in masonry construction was on hand.  She rushed in to try to assess the situation.  She found that the mortar was too soft for the large slabs of masonry.  It simply didn’t contain enough cement support the heavy roof structure.

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We knew that specialized contractors would charge triple on a holiday, so the conservator did the best she could to piece the house back together.  The result was a stabilized ruin, complete with an open roof and a bit of sagging ornament.  Some ornament had to be removed from the ruin, as it was too damaged to be reinstalled.  And sadly, a looter (aka grandpa) scavenged a few choice pieces.  But the conservator did such a good job that the ruin stood true for several hours until the house was devoured by marauding giants (aka my niece and nephew).

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Recessed Mortar

Usually when you see recessed mortar joints on a wall, it means the mortar has eroded due to weathering or water infiltration.  But in the early and mid-twentieth century, recessed mortar joints were part of the design of some buildings.  Take this wall, for example.  The mortar is recessed about a quarter inch or 3/8-inch back from the face of the brick.

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Recessed joints, sometimes called raked joints, were most popular in the middle of the twentieth century, though sometimes you can find them on early twentieth century buildings.  (I worked on a 1908 building in Manhattan that originally had recessed joints at the brick cladding.)  You almost never see recessed mortar joints on stone or terra cotta buildings; they were exclusively used on brick masonry walls.

An article in Popular Mechanics from 1958 explains how to create recessed (raked) joints:

‘Raked’ joints produce dark shadows that accent the pattern of the masonry….  To make this joint, the extruded mortar is first cut off flush with the brick, using a trowel.  After a lapse of a few minutes, when the mortar begins to congeal, the mortar joint is raked out to the desired depth.  The vertical joints are raked out first, followed by the horizontal joints. … To complete this type of a joint, a square tool of the same width as that of the joint is run over the mortar to compress it and fill all voids. (W. B. Eagan, “Eight Types of Mortar Joints and How to Make Them”, Popular Mechanics, July 1958, p. 176-178)

Recessed mortar joints were mainly an aesthetic choice by the mason or the architect.  As noted above, recessed mortar provides a dark shadow line and draws attention to the brick rather than the mortar.  Sometimes masons used dark mortar to accentuate the shadow, as in the photo below, though light-colored recessed mortar was successfully used in the wall in the photo above.  Recessed mortar joints also hide flaws in the masonry.  The wall below has uneven horizontal joints; although the irregularity is apparent, the deep shadows created by the recessed mortar make you wonder whether the shadow creates the irregular line rather than the masonry.

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One of the biggest challenges of recessed mortar joints is repointing them once the mortar begins to fail.  Many times, unskilled masons will erroneously think the recess is caused by eroded mortar.  The masons will then fill the recess with new mortar, which changes the composition of a façade from one of prominent brick to one of prominent mortar.  In the photo below, the original recessed mortar joints are visible at the center and right side of the photo.  At the far left, a mason “repointed” the mortar joints by filling in the original recess, thus changing the appearance of the wall.

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It is best to leave repointing of recessed mortar joints to skilled masons who have experience working on brick walls with recessed mortar.  They will have the necessary skill and tools to accurately repoint the wall without changing the building’s original aesthetic.

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Sloppy Mortar

Let’s look a little more closely at mortar – a key component of masonry construction.  Most of the time when a brick wall is laid up, mortar is installed flush to the face of the brick, or perhaps it has a concave or an incised appearance.  But sometimes you see sloppy mortar that projects out past the masonry, such as in the photo below.

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Usually when you see sloppy mortar on a wall, it is a clue that the wall was never meant to be visible.  When he was erecting the building, the mason of this wall probably took care to create nice, smooth mortar joints at the interior of the building.  But for the exterior, the mason probably could not clean up the mortar joints because there was another wall laid up against it.  His sloppy mortar work was exposed only when the adjacent building was demolished to create this garden.  It was entirely unintentional.

Sometimes, however, sloppy mortar was an intentional choice of the architect.  There is a style of mortar in the Front Range that I have never noticed back east: ‘weeping mortar’.  From what I can tell, it seems to have been popular between the 1930s and 1950s – perhaps even slightly later – and it entailed allowing the mortar to ooze out of the masonry while the wall was being constructed.  I saw this Tudor-Revival style building with weeping mortar joints on the University of Colorado campus a few weeks ago.

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It was built in 1931 as the Pi Kappa Alpha fraternity house, and was designed by celebrated Boulder architect Glen H. Huntington [pdf] (not to be confused with his father, Glen W. Huntington, an architect who practiced primarily in Denver).  The house was purchased by CU in 1970 and currently serves as the University Administration Building.  It was made using beautiful red and brown flashed brick, whose colors are created through a deliberate manipulation of the chemicals and temperatures in the kiln.  You can see the gray mortar ‘weeping’ out of the joints in the photo below.

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Usually a mason scrapes the mortar off the brick when he adds a new course of brick, but for this building the mortar spills were left on the brick intentionally.  The same technique was used for the small adjacent building – the University Administration Annex at 924 Broadway.

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Weeping mortar gives the masonry an interesting texture, to say the least.  I have seen the same treatment on a concrete block hotel building on East Colfax in Denver, in several mid-century neighborhoods, and on a few other buildings in the Denver suburbs.

UPDATE: I have been asked several times by homeowners whether weeping mortar can be removed. The short answer is, sure, all mortar can be removed (in theory). But I suppose the real answer depends on a the strength of the mortar, and the workmanship of the mason who will be removing it.  Weeping mortar would need to be carefully chipped off with a chisel.  An errant chisel blow to the mortar could chip the face of the brick.  Once the weeping mortar was removed, the mortar between the bricks would need to be cut back at least 1/2″ behind the face of the brick to allow the mason to repoint the mortar with a flush or concave tooling.  Weeping mortar joints are typically wider than the narrow late-19th century “butter” joints, but it would not difficult for a mason who was removing mortar to cut into the brick using a grinder.  Great care would need to be taken to prevent damage to the brick when removing weeping mortar.  In addition, the stronger the weeping mortar, the harder it will be to remove.  Weeping mortar was used on Depression-era and mid-century structures, so I would guess the mortar contained more cement than earlier mortar mixes, giving it strength and durability.  So, yes, weeping mortar can be removed from brick, but as with most repair and rehabilitation projects, it is important to hire a skilled contractor with experience working on older structures.

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