Chemistry of Lime Mortar – Neighborhood Preservation in Philadelphia

19th Street Baptist Church
19th Street Baptist Church

The Chemical Heritage Foundation released an episode of their award winning podcast Distillations.  In this episode, Randy Ruth, formerly of LimeWorks.us, discusses the chemistry behind lime mortar, historic masonry buildings and the ongoing efforts to preserve one of the finest works of notable Philadelphia architect, Frank Furness. The 19th Street Baptist Church located in South Philadelphia has been in a state of disrepair for decades.  This episode sheds light on the chemistry behind its construction and the ongoing preparation to save it.

Inside the 19th Street Baptist Church
Inside the 19th Street Baptist Church

 

 

Photos © Sean K Maxwell
Other stories related to the 19th Street Baptist Church:

Yes We Can Save The 19th Street Baptist Church

Progress at 19th Street Baptist

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Phone: 215-536-6706

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Audio Transcript Excerpts:

Randy Ruth, at the time, was the lab tech at LimeWorks.us. He bridged the gap between architects, conservators and masonry practitioners on what types of building materials to use in reconstruction and restoration of masonry projects throughout the country.

“Randy and his colleagues at LimeWorks.us based in Quakertown, Pennsylvania were brought in to try and save the 19th Street Baptist Church

We took a look at at the types of mortars that were there and by knowing that the building was built in 1874 we could gauge what those original binders were without even necessarily doing an analysis. Architects, engineers and of course masons would use the local available materials which were at the 19th Street Baptist Church primarily lime based binders.

Lime is a very general term for inorganic materials that contain calcium and it’s been use in concrete and building materials since the Roman Empire. It’s derived from limestone and other rocks that are primarily made of calcium carbonate.

Basically lime is that calcium carbonate stone and it’s put into a kiln with fuel. These kilns would then be fired up to 900 degrees Celsius or slightly above and then the resulting product is a limestone that loses about a third of its weight because it’s driving off carbon dioxide so that calcium carbonate is now becoming calcium oxide.

This is all part of what’s called the Lime Cycle. Calcium carbonate is heated to produce calcium oxide and then it’s combined with water to form calcium hydroxide. Different amounts of water is added to form different consistencies.

That process is called slaking, if just a small amount of water is added it’s going to turn into a powder. If a little bit more water is added it’s still calcium hydroxide but it’s in the form of a putty.

Once the lime is in this putty form it’s spread over bricks and stones and hardens into a solid bond.

That limestone then stays malleable and flexible in a wall system in comparison to more modern materials.

Modern materials like cement. Portland cement is the most common type of cement used around the world. It’s made of primarily alite or tricalcium silicate, a more rigid and less permeable material than lime.

You’re walking down the sidewalk and wondering why are they sectioned off in four food squares or six foot squares and that’s because Portland cement is very brittle and we have to tell it where to crack and where to go versus the lime buildings like the 19th Street Baptist Church. There are no control joints and things were able to move freely and accommodate small bits of movement because lime unlike Portland Cement has the ability to heal itself, something called autogenous healing.

This autogenous healing is part of why the 19th Street Baptist Church is still standing today but the original lime mortar is all but dissolved now and that’s why the building is crumbling.

Lime mortars as they age and as they wear, they’re meant to be replaced so there’s always a maintenance issue associated with them. I hope that there is a lot of architectural salvage that can occur to pay homage to the traditional materials that were originally by Frank Furness and his architectural team.

In essence they should be able to replenish the lime mortar in the structure, but after so many years of neglect it’s getting late in the game.”

Photos © Sean K Maxwell

Presented by LimeWorks.us
Phone: 215-536-6706

LimeWorks.us (FaceBook : Google+ : LinkedIn : Twitter : YouTube)

Yes, We Can Save The Frank Furness 19th Street Baptist Church

by Sean Maxwell 2012

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This beautiful church was designed by Frank Furness and is located at the corner of 19th and Titan in South Philadelphia.  It almost went the way of many Furness structures; due to neglect and time the church leadership is under pressure to begin repairs or plan for it to be demolished due to unsafe conditions sited by the License and Inspections Department of the city. Under the leadership of Reverend Vincent J. Smith and in partnership with the Greater Philadelphia Preservation Alliance and some volunteers, stabilization efforts have finally begun.

As the morning sun crept over the skyline on the last Saturday of April, Randy Ruth, mason and the laboratory technician from  LimeWorks.us volunteered to lead a workshop with a team of a few other volunteers to complete some small but crucial repairs on the north facing wall of the 19th Street Baptist Church.

The church has been in need of serious repairs for a number of years as observed and documented in a 2000 University of Pennsylvania report, Thesis by Molly Anne Sheehan, which show that the conditions of the church and the exterior Serpentine Stonework have continued to deteriorate steadily.

Under Randy’s supervision the team of volunteers used a lime mortar donated by LimeWorks.us for doing some in-kind repairs to stabilize the failing back-up walls behind the Serpentine stone. This lime and sand mortar reflects what would have been used originally when the church was constructed in the late 1800s. Ecologic® Mortar contains NO harmful Portland Cement and allows the building to breathe and process water as it did originally.  At some point in time, a hard and brittle Portland Cement stucco was placed over a significant part of the building, trapping moisture and leading to further deterioration of the soft, sedimentary serpentine stone and contributing to mold issues that the church basement still has to deal with today.

This was the first step in saving the most colorful building ever designed by Furness… A true master plan is needed for the next step in partnership with strong fundraising efforts to truly bring this sacred place back to its original glory.

Other stories about the 19th Street Baptist Church…

HiddenCityPhila.org

Plan Philly

Gallery photos  ©SeanKmaxweLL.com

LimeWorks.us
Phone: 215-536-6706

LimeWorks.us (FaceBook : Google+ : LinkedIn : Twitter : YouTube)