On May 16, 2018, about 1520 mountain daylight time, an experimental, amateur-built Roger G White Glasair airplane, N4EJ, was substantially damaged during a runway excursion after landing on runway 12L (9,000 ft by 100 ft, asphalt) at the Rocky Mountain Metropolitan Airport (BJC), Broomfield, Colorado. The pilot sustained minor injuries. The airplane was registered to a private individual and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Day visual meteorological conditions prevailed. The flight was not operated on a flight plan. The flight originated from the Vance Brand Airport (LMO), Longmont, Colorado about 1500 and was destined for BJC.The pilot reported that he was relocating the airplane from LMO to BJC for modification of the fuel injection system after a recent sale. He noted that his preflight inspection and run-up did not reveal any anomalies. He specifically checked the brakes and detected no problems. The takeoff, cruise, and landing approach were conducted without incident. However, during the landing rollout, the airplane started drifting to the left and he applied right rudder to correct. He subsequently attempted to apply right brake pressure to further correct for the drift as the airplane was traveling about 50 knots. At that time, the right brake pedal "went to the floor;" there was "zero" right brake available. The airplane departed the left side of the runway, crossed the grass, and came to rest on the parallel taxiway. A postrecovery examination conducted by a Federal Aviation Administration inspector revealed that the right brake line was broken near the upper end of the landing gear strut. The brake line consisted of a flexible plastic line at that location. The brake master cylinder was intact. No anomalies were observed related to the brake master cylinder or the caliper assemblies. The airplane was equipped with a free castering nose wheel and did not have any nose wheel steering capability. Directional control during ground operations was maintained with differential braking.