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Trimbloid X and COR-TEN Steel

by Keith M. Bouchard, E.I.T.

If you have ever walked, ran, biked, roller-bladed, or spent any time at all on Boston’s Charles River Esplanade, it’s likely you have come across the sculpture Trimbloid X.  The sculpture, which was created by the late artist David Kibbey in the early 1970’s, has had a prominent position in Boston’s signature park for a number of years. 

Trimbloid X is a three-dimensional X-shape standing ten feet tall and fabricated from COR-TEN (weathering) steel sheets that were bent and welded together.  As was common for sculptures at the time, the artist chose COR-TEN steel for its distinctive red patina and its corrosion resistant characteristic that would presumably allow the sculpture to be displayed outdoors for many years to come. 

However, as has become well understood in the years following the creation of Trimbloid X, COR-TEN and its weathering steel successors are not as resistant to corrosion as the industry initially claimed.  It is true that if exposed to intermittent wetting and drying cycles, COR-TEN steel will form a protective red patina that will prevent further corrosion of the underlying steel.  Unfortunately, in cases of ponding water or constant moisture, the protective patina will not form and the steel will be susceptible to continuous oxidation until eventually the full section dissolves.  There is no better example of this regrettable fact than Trimbloid X.

The natural shape of Trimbloid X funnels water to the center of the sculpture where no means are provided to whisk it away.  The standing water eventually ate through the center of the object, allowing moisture and organic matter into the hollow “legs” and accelerating the deterioration.  Add years of delayed maintenance and the result is what you’ll see if you stroll down the Esplanade today – gaping holes in the side of the sculpture, trails of corrosion down the legs, and protective fencing to keep the public away from its sharp, rusty edges.

This is the condition that CBI found the sculpture in when we were engaged by the Department of Conservation and Recreation (DCR) to assess the condition of the sculpture and provide repair schemes and estimates.  DCR has a very limited budget for the repair of the object so CBI explored a variety of different options to re-establish the structural integrity of the object while respecting the original artistic intent.  These include reinforcing the sculpture in the field, shop-repairing the object with new weathering steel and possibly painting with a weather-resistive coating, and “skinning” the object with new weathering steel sheets.  Each of these options has pros and cons with regards to ease of construction and respect to the sculpture as well as cost.

Through consultation with steel fabricators and DCR, CBI recommended that the object be disassembled and repaired in the shop with new weathering steel patches.  Coating the sculpture with a patina-colored paint was not recommended for concern that it would interfere too much with the “industrial” look of the original sculpture.  The existing patina on parts of the sculpture to remain will need to be sand-blasted off to attempt to match the new steel.  The owner was warned that even with this measure, there is no guarantee that the original steel will closely resemble the repair steel.  As one steel supplier noted, different batches of weathering steel are like “trees in a forest: they all basically look the same but no two are alike.”  However, with the severe level of deterioration present on the object and the limited budget, this is likely the best the owner can do short of completely re-sculpting the object.

If you would like further information, or would like to discuss a current or future project with us, please contact:
Jenna Kotarski
250 Dorchester Avenue
Boston, MA 02127
(617) 268-8977
jkotarski@cbiconsultingllc.com