Effective caulk repair on aging cement board siding butt joints, featuring TX-1 caulking. Butt joints are the points where two siding pieces meet end-to-end. Proper caulking and sealing at these joints are crucial to prevent water infiltration and maintain the integrity of the siding system. Watch now for a resilient weatherproof technique. Diagnosing and addressing common issues with older siding. Keep in mind that newer Hardiplank siding does not require caulking at the butt joints.