Walking around most neighborhoods in Portland, Oregon you may notice street names, dates, and contractor’s names stamped into the concrete sidewalk. Most of these date to the early 20th century, at a time when the city’s streetscape was solidifying through the use of asphalt and concrete.
Sidewalk stamping in the U.S. became popular toward the end of the 1800’s, when brick and board walkways were gradually being replaced by concrete sidewalks and curbs. Today, signs with street names are designed for drivers. Though they acknowledge the existence of pedestrians and other users by minimum clearance heights and other standard dimensional requirements, these and other geographical markers are predominantly focused on directing vehicular traffic. Concrete stamping however, is a specific marker designed for the pedestrian. As pedestrians move through the streets, stamps provide an easy, natural way to identify their location. Having recently moved to a new neighborhood, I personally appreciate these 100+ year old stamps as I walk down my new streets.
The photo above was taken in my neighborhood at a new ADA-compliant pedestrian ramp which was cut into an older portion of sidewalk. In these confluence areas of old and new, Portland has often impressed the construction dates of old and new sidewalk into the new concrete. This is a trend fairly typical of many cities besides Portland, and one which reflects respect for our historical infrastructure.
As the photo above shows, some contractors stamped their company name in the fresh concrete. This simple advertising was also a mark of craftsmanship. This pride in craft is admirable, and shows true confidence in quality workmanship – especially given the nature of sidewalks which are meant to last for decades. It’s impossible to know how long these contractors thought their work would endure, but it is a testament to their superior skill that so much of this older sidewalk is in exceptional shape.
A portion of the public art for the new Portland-Milwaukie light rail project will be used to incorporate phrases and poetry in the form of stamps in sidewalk panels. Read about the proposed impressed concrete here: http://orangelining.net/?page_id=228. This project recognizes that concrete stamping is not only valuable for navigation, it also offers a great aesthetic opportunity.
Concrete stamping is a relatively simple process, though it does require attention to some key details. The stamp should be designed for the reality of concrete sidewalk and the concrete mix design used. For example, a small-lettered stamp will not be suitable for sidewalk with a larger aggregate mix, as it will be difficult for the letters to fit with the aggregate (and for the finished stamp to be structurally strong enough to last a significant amount of time). Timing is also a crucial element, as stamps must be impressed into relatively wet concrete, though the surface must be stiff enough to hold the pattern of the lettering. Likewise, the force used to stamp concrete will have a significant effect on the impression that is made – too hard and the impression will be too shallow, too soft and the letters will smear together. Oil or powder on the stamp helps to release it from the concrete and create a more consistent finished product.
Given the relative ease of concrete stamping and its durability, it is not surprising that this municipal streetscape element is still popular today.