Rock　wool　belt　is　one　form　of　rock　wool　products　used　in　external　thermal　insulation　composite　system.　However,　a　related　and　important　problem　is　how　to　improve　bonding　strength　between　rock　wool　belt　and　adhesive　mortar.　The　present　work　studies　the　effect　of　interface　agent　on　bonding　strength.　After　interface　agent　was　applied　on　the　surface　of　rock　wool　belt,　the　original　strength　and　water-resistance　strength　increased　remarkably　with　the　increasing　of　the　concentration　of　interface　agent,　and　the　maximum　value　was　almost　7　times　over　that　without　interface　agent.　It　was　believed　that　the　significant　increasing　of　bonding　strength　was　related　to　fiber　structure　of　rock　wool　belt,　correspondingly,　the　interface　agent　could　improve　effective　bonding　area　and　increase　the　bonding　depth.　Moreover,　it　is　worth　noticing　that　the　drying　time　of　the　interface　agent　had　little　effect　on　original　strength　and　water-resistance　strength,　so　it　needn＇t　a　strict　time　requirement　for　rock　wool　bonding　construction　after　applying　interface　agent.　©　2017　Trans　Tech　Publications.