Picking the Right Product for the Job
Labor, materials, consultations, and other similar expenses are
all factors that can really rack the price up of any restoration or
construction project. Everyone would agree that the lower the cost of these
expenses the better; however, always choosing the cheapest option may not be in
the best interest for your project.
Choosing the right materials that will perform over the lifespan of your structure should be your highest priority because that will save you the most money and time in the long run. The cheapest, quickest option, like using a Portland cement-based material where not suitable, can carry many unintended consequences in the future for your historic structure.
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LimeWorks.us was commissioned by Zion Evangelical Lutheran Church of Tamaqua, Pa., to diagnose and address the failure of a church tower which utilized man-made cast stone for trim details. At the time the original building was built in 1914, as a cost-effective solution, Zion Evangelical Lutheran decided to use the cement-based cast stone. Almost 100 years later, a first and second campaign was undertaken to repair the cast stone by using modern Portland cement and sand in a compound made to carry out the repairs. Both campaigns failed within a few years of their installation.
Why Did the Cast Stone Fail?
One of the most common problems associated with cast stone is its propensity to shrink and crack when the cast does not cure sufficiently.
After our evaluation of the facade, we believe the use of Portland cement in the application of the repair material caused the water that entered the system to activate the solution sulfates already present in the structure and deposit additional sulfates into the system. If these sulfates crystallized beneath the surface then the cast stone would begin to deteriorate.
Pro Tip: When salts crystallize, a force of about 4000 psi is exerted (about the same force as a saltwater crocodiles bite strength (3,700 psi)
The “accumulation of water-soluble salts that re-crystalize just beneath a masonry, stucco, or concrete surface,” is known as subflorescence. This subflorescencent activity beneath the cast stone, along with freezing and thawing would first form minute micro fissures that lead to larger cracks after multiple freeze/thaw cycles.
Some Portland cement-based materials can even innately contain “soluble salts such as calcium sulfates and sodium… which can leach out over time” and begin to break down the existing mortar and stone. Cast stone is a cheaper alternative to using quarried stone, which is highly labor intensive and cost-prohibitive. Using a cast stone cement mix was well intentioned and even took into its purview the original building material. However, using the exact building material to create an exact historic replica is what caused the first cast stone patches to fail. A closer historic simulation can more effectively be achieved by using lime in the restoration process, because of its workability and chemical properties.
Using Lime to Mitigate Environmental Factors and Save Money
Heritage conservation, sustainability, and environmental factors should come into play when approaching your restoration project. Materials such as our Lithomex, Lithostep, and Lithocast were used in the restoration process in order to address the underlining issues which caused the cast stone patches to fail. Our Lithomex products are created primarily from pure St. Astier brand natural hydraulic lime and aggregates.
Overall, the Lithomex products have a good modulus of elasticity and an excellent water permeability which enables Lithomex to re-release water back to the atmosphere before it has time to freeze. Since there is no common building stone on our planet that can re-release water back to the atmosphere quicker than Lithomex, water can never get trapped behind the patch. Trapped water which freezes and expands can push off stone repair patches. This is the biggest problem with many commercially available and, yet, exorbitantly expensive stone patching materials on the U.S. market.
By using lime-based products in the restoration of the church, we will mitigate the environmental and material related factors that caused the previous stone patches to fail while also increasing the over-all longevity of the church building.
The Restoration Process
In our restoration of the stone tower the LimeWorks.us Technical Install Team removed the corroded cast stone down to sound material and then used our Ecologic Waterglass as a conditioning primer to stabilize the loose powdery particles on the surface of the cast stone before carrying out the detailing for final cast stone repairs. This will ensure that our Lithomex patches will bind to the wall and not fall off due to a corroded application surface (see Figure 3).
After the Waterglass cured, we installed an armature (interior skeletal structure) of stainless-steel rods and wires to create a mechanical connection between the new mortar and the original cast stone surface (see Figure 3). The chemical properties of the lime mortar will allow water to exit the structure because of its high porosity, which combined with the mechanical structure of the armature will hold the material there for years to come.
Many of the columns were so deteriorated that
they had to be rebuilt by hand. Our expert craftsmen hand tooled our St. Astier
Lithomex to give the surface of the columns a rough, aged look that would
simulate the natural appearance of the original elements.
The Technical Install Team cleaned and repointed the existing ruled ribbon joints around the granite and created a custom mortar simulation of the original pointing mortar. Visible in Figure 5 is the new repointing work. We performed a light and diluted wash down using NMD 80 50/50 with clean water for cleaning sharpening the lines of the repointing work along with slightly raising the grain of the aggregate so the new work would compliment and blend in with the remaining original working mortar.
Restoration Project Before and After
Do Your Research First and Pay Less Later
When approaching your next restoration project, remember to consider the long-term effects the materials you employ may have on the building you are attempting to repair. Just choosing the cheapest alternative or the original building material may not always be the right option or save you the most money in the long run. Lime’s ability to allow water to pass through a structure, its resistance to sulphates and salts, and its elastic properties make it the perfect solution to fix the problems caused by the use of Portland cement on Zion Evangelical Lutheran Church. To learn more about our lime and how it may be able to save you a headache in the future visit https://limeworks.us/about/lime/.
Interested in the work we did at Zion Evangelical
Lutheran Church? Join us for our next hands-on workshop at The Craftwork
Training Center and increase your knowledge in the field of historic masonry
restoration! Visit https://limeworks.us/events/hands-on-workshops/
to learn more.
(Page 7-8) Man Made Vs. Natural Stone A Study On Cast Stone https://ilco-indianalimestone.netdna-ssl.com/wp-content/uploads/2016/01/caststone-whitepaper.pdf
 (Page 63) LIME MORTARS FOR THE CONSERVATION OF HISTORIC , BUILDINGS https://pdfs.semanticscholar.org/4b5b/b5290e75c12a219ecc0c23ab78004e2968aa.pdf
 (pg. 10-11) LIME AND ITS PLACE IN THE 21ST CENTURY: COMBINING TRADITION, INNOVATION, AND SCIENCE IN BUILDING PRESERVATION, https://limeworks.us/wp-content/uploads/2017/07/LimeAssociation.pdf