Stone Masonry at 4 Mercer Street


Often referred to as the Town Topics Building, 4 Mercer Street was constructed in 1878 and is located within the Mercer Hill Historic District of Princeton, New Jersey. HMR Architects is currently working with Princeton University to adapt and rehabilitate the interior of the building while also improving various site conditions.

The rehabilitation includes the creation of two apartments and one townhouse on the upper floors. The ground floor will be renovated for use as University office space. The improvements include a new accessible entrance while maintaining the historic storefront on Mercer Street. This project is being constructed as LEED equivalent.

The Problem

The brownstone sills at the storefront have delaminated over time, due mostly to the fact that the original stone was set with the bedding planes in the wrong direction. Brownstone, being a sedimentary rock, must be set so that the bedding planes are parallel to the ground. Because these sills were set with the bedding planes perpendicular to the ground, over time the layers of the brownstone delaminated from the front face, instead of compacting down vertically and strengthening the sill, as the design intends.


As this is the main street-facing façade, it is important that this be preserved and restored to its original historic integrity. If nothing is done, the stone will continue to deteriorate, allowing water to get into the building and further damage the foundation and finishes.

The original stone was damaged beyond repair.  Alternatives to replacing the whole stone were reviewed, however, these did not provide the long-term solution that we were looking for. Once it was decided that the stone had to be replaced, we had to figure out where to find it…

The Challenge: Finding a Replacement Stone

Despite its widespread use in the construction of over 50,000 row houses from Baltimore to Boston in the 1800s, Brownstone is no longer a commonly used building material, and can be difficult to find.

The ‘Bone Yard’ is the area where the University keeps all of its salvage from the buildings they own. Lucky for us, they had a matching stone in the yard, allowing us to bypass the arduous process of sampling stones from local quarries. Finding and then cutting the stone could have taken months and would have been very expensive.


When matching the stone, there are two things to consider: 1) we look for a color match to maintain the aesthetics of the building, and 2) the bedding planes must be in the right orientation or the new stone will deteriorate the same way the old one did.

Finding the matching stone in the bone yard was a fortunate discovery because the stone was delivered, cut and installed in a period of three days instead of what could have been months. This was an integral part of keeping delays to the project schedule at a minimum.

The Result

Once the University had the stones delivered to the site, HMR worked with Joseph Dugan, Inc. to cut and install them the next day.


This stone replacement was a success because the historic character of the façade was maintained while keeping cost and time down to a minimum. The new sills will provide a sound substrate for the installation of the storefront façade and will last for many years to come with minimal maintenance unlike other alternatives.



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