Exteriors of older buildings present challenge.

Historical and older buildings present a unique challenge in the field of exterior restoration and waterproofing because they combine a variety of construction methods with the brick, terra cotta, and brownstone materials favored in earlier periods.

Preventive maintenance is the key to retaining the property's aesthetic and structural integrity. A case in point is the American Stock Exchange (AMEX) located in Lower Manhattan. They decided to combine a complete restoration and repair program with the periodic Local Law 10 facade inspection required by the City to correct any hazardous conditions that might exist.

Their approach was to survey, pinpoint and restore all areas with varying degrees of deterioration before the problems become more costly or impossible to solve.

To assess facade conditions at the headquarters on Trinity Place, and at a brownstone around the corner at Greenwich and Thames streets, AMEX turned to Lester Karstadt, PE. Unable to "see the building" due to significant dirt build-up on the facade, his first step was to recommend cleaning.

AMEX chose Lime Contracting, Inc., a firm whose "credits" included the Empire State and Puck buildings, properties whose exterior materials were the same types of limestone, brick, terra cotta, and brownstone materials used for the AMEX buildings.

Experience with these specific materials is important. Though contemporary science provides a full range of chemicals and inventive tools for cleaning, modern technologies need to be combined with "old fashion" experience to be successful and are not always the best ones to use on older structures.

We had to work with the building by carefully analyzing the materials and their level of deterioration before deciding on cleaning and restoring methods.

That's the fundamental process we followed when we sat to work out our "low-tech-first" approach. Though the buildings don't have official landmark status, Lime decided to use landmark quality techniques.

The safest way to proceed was to begin with a basic non-corrosive technique. Lime's experts tried an old-fashioned water wash: a "gentle rain" soaking and softening the grime over a 24-hour period, followed by a medium-pressure hosing. A test area proved the technique to be effective and Lime's crews set to work scrubbing the buildings down.

A "gentle rain," however, would not work on everything. Carved surfaces and extra-heavy accumulations of grime resisted this less abrasive effort.

Lime's crew of Local 66, Pointers, Caulkers, and Cleaners, worked with different types of scrubbing brushes and a variety of cleaning agents formulated for older buildings.

As the scrubbing revealed more and more of the facade, Karstadt followed up with repeated inspections. Now the years of wear began to show: deteriorated stone, missing mortar, crumbling brick.

High-tech was helpful here for "state-of-the-art" repairs. Concrete-based polymer patching materials, such as special composition mortar, were applied by master mechanics, making patches invisible.

There was one area where there was some concern about obvious differences between the original and the restored areas. But once we had made the repairs, no one could tell the difference.

In some instances, masonry damage was so great the only solution was replacement. That's difficult when an unusual brick has been discontinued. Tom Corbo, Lime's chief operating manager spent several months visiting dealers looking for the right match. He found it in the town where he lives.

There were some pleasant surprises too, Karstadt reports. Inspecting the cleaned terra cotta, he discovered that the unglazed variety used by the original builders had withstood deterioration far better than some of the newer glazed terra cotta brick.