J molding is a type of molding used to present a finished edge on vinyl or aluminum siding. It is used around window casings and door casings and at the top edge and bottom of the siding to hold siding in place.Click to see full answer. Thereof, what is J trim for?J-Trim is a material used to perfect the edge on aluminum or vinyl siding on a home or small building. You will see this trim around windows and doors and at the bottom and top of the siding so that it may be held in place.Furthermore, how do you install J trim on drywall? How to Install Vinyl Drywall “J” Bead Hook the tape measure’s tang on end of the bead. Cut along the mark with a pair of snips. Spray drywall bead adhesive along the drywall sheet’s edge and throughout the bead’s center channel. Align the bead’s channel with the drywall’s edge. Slip one end of the bead over the drywall. Also Know, what is AJ Mould? Flannery’s J-Mold is a termination trim that is used to terminate stucco, veneer plaster, drywall or wood panels. Typically installed where a stucco wall terminates at an opposing wall or dissimilar material, the J-Mold can act as a stucco stop.Do you overlap J channel? Overlap Your Top J-Channels There’s no way to stop rainwater from getting into the J-channel that sits on the top of windows and doors. But you can stop that water from getting behind the side J-channels. Create a flap in the top J-channel that overlaps the side channels.