The pilot of the tailwheel-equipped airplane reported that he conducted multiple passes over the landing area to assess the landing conditions and did not see that the grass surface was wet. Upon touchdown, he noticed the airplane did not decelerate as expected due to wet tires, and the brakes had little effect. The airplane veered off its intended path, heading toward steep downhill terrain. To prevent continuing uncontrollably downhill, the pilot attempted an intentional ground loop by applying full right rudder and power. Subsequently, the airplane tipped left and stopped before reaching the steeper terrain, resulting in substantial damage to the left aileron and left elevator. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.