Archive for category Limewash
An Interview with Lauren McCroskey, U.S. Army Corps of Engineers – Revised UFGS Historic Masonry Specification
I had the unique privilege to interview one of the leading historic preservation experts, Lauren McCroskey, Program Manager, for the U.S. Army Corps of Engineers, at the Seattle District, on the recent revision to the UFGS for the Restoration and Cleaning of Masonry in Historic Structures.
USACE Official Announcement:
Technical Center of Expertise (TCX), Preservation of Historic Structures and Buildings Technology Update
As part of its mission to provide leadership in historic buildings technology, the TCX announces a major revision of its specification, “Restoration and Cleaning of Masonry in Historic Structures.” The spec now reflects state-of-the-industry guidance for the treatment of historic masonry and mortar, and surpasses existing preservation guidance provided by other federal agencies.
Property managers and cultural resource specialists are encouraged to use the spec in contract documents to ensure that masonry work is performed appropriately to prolong the life of historic buildings. See Unified Facilities Guide Specification 04 01 00.91
Speweik: What is the official title of the specification?
McCroskey: The title is the UNIFIED FACILITIES GUIDE SPECIFICATIONS
DIVISION 04 – MASONRY SECTION 04 01 00.91
RESTORATION AND CLEANING OF MASONRY IN HISTORIC STRUCTURES
Speweik: Who originally authored it?
McCroskey: The Corps was the preparing agent and performed the processing. The exact author(s) are unknown, though Corps staff would have prepared it.
Speweik: How long has it been in use/circulation?
McCroskey: It’s been available since 1991.
Speweik: Who is authorized to use it?
McCroskey: The Guide is to be used by the Military Departments (Army, Navy, Air Force, etc.), the Defense Agencies and the DoD Field Activities for planning, design, construction, sustainment, restoration and modernization of facilities, regardless of funding source. But anyone can use the guide to adapt to a particular masonry project.
Speweik: What government agency owns it?
McCroskey: The Architectural Discipline Working Group are the owners of the Section; Scott Wick is the Corps representative of that group.
Speweik: What is your position with the USACE and what specific responsibilities do you have regarding historic preservation?
McCroskey: I manage the Technical Center of Expertise for the Preservation of Historic Structures and Buildings, a program of nationwide service. The program provides technical assistance and preservation planning for Corps Districts, DoD, and other federal agencies to ensure facility and property managers apply the best practices to historic structures. We try to set the highest standards of preservation practice through quality project work, training, and by developing technical information.
Speweik: What prompted you to request an update to the Historic Masonry Division Section this past year?
McCroskey: For several years I’ve had an awareness that the Corps’ existing standards and guidance for the treatment of historic masonry has lagged behind newer developments and technological advancements for treating historic brick, stone, and mortar. I receive inquiries from Corps Districts and other agencies asking for specific guidance to address deteriorated stone or brick. Property managers rarely know how to approach these issues from a historic preservation perspective, and often have maintenance and field crews tackle masonry problems. While their intent is good, the methods, materials, and applications are often not appropriate for historic structures, and can lead to further harm and long-term costly repairs. That’s why it’s essential for us to be able to pass along the most appropriate, state-of-the-industry techniques and standards.
Speweik: What do you believe to be one of the most significant changes to the specification?
McCroskey: There are many improvements, but one of the most important is the depth of information, which is far more educational for the user than the old spec. There is much to be learned from this document. Another key improvement is that materials application is not just described, but preceded by a thoughtful examination of building and masonry conditions. There is extensive information about how to investigate existing conditions so that the best decisions can be made about materials, conditions, and methods.
Speweik: How do you see this change making a positive difference for the quality-level of Historic Preservation Projects in the United States?
McCroskey: I believe the TCX is obligated to provide the best guidance regarding the treatment of historic structures and buildings. By encouraging the use of this guide, the rehabilitation of historic masonry should be performed in a manner that is appropriate, efficient, and prolongs the life of historic materials.
Speweik: How do you envision the revised specification affecting the work you do at the USACE?
McCroskey: The spec will be the only guidance we provide to customers, or when advising others on the best standards for masonry. Since this spec now surpasses all other historic masonry guidance, we now consider this document the “gold standard.” Of course, there are sub categories of masonry, such as terra cotta and concrete, which may require other technical information. But where brick, stone, and mortar are concerned, this is our “go to” standard.
Speweik: Did you consider the possible additional costs to Historic Preservation Projects as a result of some of the changes? And, if so, do you believe the additional cost is a significant percentage of overall project costs?
McCroskey: When good preservation practices are used, the life and performance of historic materials is extended. When improper practices are applied, greater costs can be incurred when the wrong treatment or method causes damage that requires repair. Taking short cuts by using commercial products that are not suited to historic stone or brick, or using techniques that are not consistent with historic methods can cost more long-term, and rarely satisfy the Secretary of the Interior’s Standards for Rehabilitation and treatment of historic structures that all federal agencies must follow.
Speweik: How do architects, owners, consultants and contractors find out more about this important specification document?
McCroskey: The guide is now available on-line at the TCX web page: http://www.nws.usace.army.mil/BusinessWithUs/HistoricPreservation.aspx
For additional information or clarification regarding the spec’s application, your readers may contact me at:
Technical Center of Expertise
Preservation of Historic Structures & Buildings
U.S. Army Corps of Engineers
Whitewashing has been used for many years to cover and protect historic masonry, even before it was historic! A whitewashing application involves mixing lime putty with water in a ratio of 1:5 then vigorously stirring the material until the lime putty fully dissolves in the water. Colors can be added from earth pigments but most material was used white – thus the name. The lime (calcium hydroxide) sets slowly by absorbing carbon dioxide from the air. The chemical reaction that occurs produces crystals of calcite. These crystals are unusual because they have a double reflective index: light entering each crystal is reflected back in duplicate. This results in a wonderful surface glow that is characteristic of whitewashed surfaces and is not found in modern paint products or imitation coatings.
The application of whitewash acts more like an absorptive stain. It is not a coating so it will not peel-off. After it hardens whitewash remains vapor permeable and will not trap moisture in the wall. One of the attractive attributes is that it gradually wears off the surface of the wall over time leaving a very pleasant uneven aged look.
Many architects and designers seek this look but have had challenges because they have been using the wrong products, such as paint, to achieve the effect. If it is a traditional look you want to specify than its best to go back with the traditional material that will get you there.
The key; however, is in thinly applied coats. This facilitates the carbonation process of curing and prevents crazing and cracking. It is helpful to specify onsite application training – as most painting contractors will treat the product like paint and attempt to get the surfaces coated in paint-thickness applications. Most raw masonry surfaces require 3 to 5 applications of whitewash, then after that, just a single coat will do the trick to freshen things up later.
Additional reading: http://www.slideshare.net/speweikpreservation/speweik-limewash-returns-2000