Mapei’s Ultrabond ECO 995 urethane wood adhesive achieved a rating of 50 for both STC (Sound Transmission Class) and IIC (Impact Insulation Class) in recent documented sound testing reports, the company said. In addition to these sound-reduction qualities, Ultrabond ECO 995 acts as a crack-isolation material that can handle cracks in concrete subfloors up to 1/8 inch wide.