Trim Board At Bottom Of Siding . While paint does tend to somewhat glue these pieces together, caulking them is never advised and can cause permanent damage. When replacing siding, try to purchase a piece from the same manufacturer in the same color. Brian's Life How to replace rotted T111 siding with a belly band from www.brianhensley.net Installing hardietrim boards on inside exterior corners is necessary to finish siding courses, but it also adds color and emphasizes a home’s height with a strong vertical line. The bottom portion of a panel of vinyl siding that locks into a previous panel that was just installed. In the old days, the builder would install the trim, bring the siding up to it, and caulk the corner.