Ashlar Masonry Quoin Corners

Ashlar masonry quoin corners are found at a handful of buildings here in Capitol Hill.

Masonry structure corners provide significant structural strength.  Quoin corners can be built with accent brick, cement units, ashlar stone (such as in the following picture) and even with rubble stone.

20170409_160506

Click here to go to the list of all items on Capitol Hill Historic Masonry. 

Jack arches

Jack Arches are common in Capitol Hill.  They work well with a tall rectangular window with the inside of the window close to the underside of the ceiling on the interior side of the building.

Jack arches are also sometimes referred to as “flat arches” or “straight arches.”

A jack arch is an alternative to a one-piece  lintel, and the individual units in the jack arch make it easier to lift and hoist than a heavy solid lintel.

The jack arches shown in the photo below are here in Capitol Hill.  This is a bonded arch, with about a 60º skewback. The greater angle creates more stability.

20170409_160408

Click here to go to the list of all items on Capitol Hill Historic Masonry. 

Non-Ashlar Cobble Footings and Walls

Sometimes called “Rubble Masonry,” non-ashlar consists of laying material that is not uniform — in most cases, different sizes and shapes of stone set in mortar.  Many historic foundations are built using this technique. However, the homes on Capitol Hill built in the late 19th century and on were primarily brick.

Historic rubble foundations were convenient because the stone did not need to be refined or “faced” to create smooth flat surfaces. A soft mortar was used for construction. Its purpose was, in some cases, more to provide an even bedding place that would fill all voids between the different sizes and shapes of stone and prevent shifting.

Today, most buildings with old non-ashlar foundations can be refurbished by tuckpointing the affected areas, as no stones have shifted a great deal.

Many historic buildings were also built with above-grade walls made from non-ashlar masonry.

A local Capitol Hill friend and neighbor sent picture of their barn in Pennsylvania.  This is barn is a beautiful example of rubble masonry that has stood the test of time.

Click here to go to the list of all items on Capitol Hill Historic Masonry. 

CBA of brick vs alternatives

Advantages of Brick

  1. Does not burn
  2. Raw materials are cheap, making it economical to produce
  3. Reusable
  4. Versatile size, shape, and texture
  5. High compressive strength
  6. Low maintenance

 

Disadvantages of Brick

  1. Time-consuming building process
  2. Poor seismic rating
  3. Prone to efflorescence due to moisture permeability
  4. Low tensile strength

Click here to go to the list of all items on Capitol Hill Historic Masonry. 

 Mortar to brick ratio

In general terms —between masons — a thinner mortar joint is a sign of higher quality work, but require higher labor and skill. In comparable terms, mortar is cheaper than the masonry unit. So sloppy wide mortar joints are cheap, while thin and neat mortar joints are expensive.

In Capitol Hill, the front façades are often a higher-quality, more evenly-sized and shaped pressed brick, while the sides and rear façades are of a less-consistent, less expensive common brick.

Common brick with thick and sloppy mortar joint.

Pressed brick with thin and neat mortar joint

The brick on the right is the brick at the side of the building. The brick on the left is the face brick, made of pressed brick. You can see there is a Tidewater joint in the pressed brick; at the right (in the common brick), there is a much wider mortar joint.

Click here to go to the list of all items on Capitol Hill Historic Masonry. 

Weeps to relieve retaining wall hydrostatic pressure

Capitol Hill is home to many historic retaining walls built from brick or stone. Many homes with English Basements have a lower entrance that is sidewalk level and/or feature a raised garden in between the door and the sidewalk.

Hydrostatic pressure often builds behind these walls and, with nowhere to go, can start to damage the structure. Common indications are deflection and loreal destabilization of the wall.  An early sign of that the wall may be failing is efflorescence — white stains that build up on the surface of the wall generated by salt deposits as moisture permeates the masonry. If a problem is left unchecked, you might eventually find spalling, where the brick starts to flake apart.

Moisture issues can typically be avoided with the installation of a weep — essentially, a small gap in the masonry structure that allows hydrostatic pressure to drain out. A drain will also alleviate moisture problems. These are typically a perforated drain pipe or tile set into an aggregate stone bed and wrapped with a filter fabric.

The vast majority of Capitol Hill retaining walls were surprisingly built without weeps.

A typical granite retaining wall, with significant deflection failure without weeps.

Click here to go to the list of all items on Capitol Hill Historic Masonry.