This week’s dramatic roof collapse in downtown McComb, which was possibly brought on by a combination of hard rainfall and clogged or inadequate downspouts, has brought home again the need to maintain our historic buildings. Luckily for us, while owners of new buildings are on their own for advice about maintenance, historic building owners have the expertise of the National Park Service to help us understand the best treatments for our buildings. The NPS Preservation Briefs series contains 49 bulletins on a variety of issues common to historic buildings, including how to deal with different materials and construction methods, so we can be stewards of these historic places for the next generation.
Beginning today with concrete, we start a MissPres occasional series that will introduce you to individual briefs and give Mississippi examples of each.
Concrete is an extraordinarily versatile building material used for utilitarian, ornamental, and monumental structures since ancient times….While early twentieth century proponents of modern concrete often considered it to be permanent, it is, like all materials, subject to deterioration. (Paul Gaudette & Deborah Slaton, Preservation of Historic Concrete. National Park Service, U. S. Department of the Interior, Heritage Preservation Services)
According to Gaudette and Slaton, Jackson’s Bailey Middle School “…exemplifies the applicability of concrete to creating a modern architectural aesthetic.” Those of us who love N. W. Overstreet and A. Hays Town’s 1936 PWA funded building wholeheartedly agree. Bailey was one of many concrete buildings designed and constructed under the Public Works Administration.
Improvements in concrete quality and protection against corrosion became better understood as the process developed (Gaudette & Slaton), and the ability of how to assess and evaluate concrete structures to preserve them “…for future generations while minimizing impact [of intervention] and not compromising safety of the users or the stability of the structure” became an increasing concern to historians and others in the preservation field. (Crevello, Hudson, & Noyce, 2015)
The National Park Service’s Preservation Brief # 15 on historic concrete identifies several causes of deterioration of concrete buildings, including the corrosion of the embedded steel reinforcements, improper methods of construction, and structural problems. Climate, exposure to water or high humidity, and high amounts of chloride (from sea water, de-icing salts, or construction inadequacies) can accelerate the damage to steel-reinforced concrete and cause rust. Rust expands, needs more space, and this expansion can result in cracking and spalling of the surrounding concrete. Spalling occurs when surfaces of concrete exposed to the corroded steel of embedded supports literally fall off the surface. A potential indicator of future spalling is rust staining on the concrete. As Malvaney pointed out in “Why Bailey Jr. High Needs Fixing” the clay sub-structure of many parts of Mississippi soil–including the soil under Bailey–can exacerbate cracking and spalling due to the expansion and contraction of the soil during periods of wet and dry spells.
Examples of corrosion and cracking on Bailey can be observed in the photographs below. Importantly, what is to be done about it?
Evidence of moisture movement through concrete is apparent in the form of mineral deposits on the concrete surface. Cyclic freezing and thawing of entrapped moisture, and corrosion of embedded, reinforcement…contribute to deterioration… (Gaudette & Slaton)
The significance of a historic concrete building or structure–including whether it is important for its architectural or engineering design, for its materials and construction techniques, or both–guides decision making about repair, and, if needed, replacement methods. With historic concrete buildings, one of the more difficult challenges is allowing for sufficient time during the planning phase to analyze the concrete, develop mixes, and provide time for adequate aging of mock-ups for matching to the original concrete. (Gaudette & Slaton)
The accepted process for planning, assessment, and intervention are:
- condition assessment,
- implementation of overall maintenance plan,
- surface preparation,
- repair materials and mix design,
- replacement if beyond repair, and
- protection systems.
In December 2016, the Bailey school project was awarded a Community Heritage Preservation Grant of $370,000 toward the larger cost of intervention for “stabilization of the structure and restoration of the classrooms and auditorium.”
Mississippi enjoys a number of concrete buildings, many of which have been featured on Preservation in Mississippi in the past. As sturdy and ever-lasting as concrete may seem to be, planning for concrete preservation is critical for these buildings to still be with us in the future. Preservation Briefs, brought to you by the National Park Service, provide guidelines for the planning for preservation of many historic buildings and unique features, in addition to preserving historic concrete structures. You can download the pdf, or read it online, at either of the links to the National Park Service page. Unless we act soon, some of our historic buildings may not survive the damage that is eroding the stability of the buildings, and their contribution to our communities will just be another photograph somewhere or a fading memory. A few of Mississippi’s unique concrete buildings are presented below, both those that have been maintained or repaired, and those that still need a little work so that they will be around another 80 years.