Contractors building a wooden balcony on a Rockville hotel were not using the proper support device -- a metal brace designed to sustain the strain of wet concrete -- when the building collapsed May 18 and injured five workers, according to a Rockville building inspector report.

Robert Groff, city superintendent of licenses and inspections, said yesterday that no one has yet taken responsibility for the collapse but that the omission of the metal hanger, a common U-shaped support device, is an unusual mistake for the contractor, Hardage Enterprises Corp. of Wichita, Kan.

The company also was required to have a city inspector review the site before the concrete was poured, Groff said. According to city records, the contractor called in a request for an inspection by 8 a.m. that day, a half hour after city inspectors had begun their daily schedules, Groff said, and no inspection had been done by the time the concrete was poured.

Thomas Eastwood, president of Hardage, said yesterday that his company was "very upset and embarrassed" about the accident and supervisors were "doing everything to prevent another mistake."

The building collapsed early in the day as five workers were pouring concrete on the south side of the 203-room hotel near I-270. The third-floor walkway fell onto a second-floor walkway and both levels hit the ground. Groff said the area that collapsed was supported by a beam that had been fastened by six 16-penny nails to a column behind the third floor.

Groff said the city had not fined Hardage for missing the inspection -- a $100 fine -- because the company was losing money from the work stoppage and "we haven't had any problems with these people before."