After all the components of a sash are repaired or replaced, the sash is now ready to re-assemble. Connect the mortises and tenons on the four outside corners using epoxy adhesive. Install original wooden pegs. Place the sash is flat on a work table, square up and brace it until the epoxy dries. Only the corners should be glued. No muntins are glued together; they should be free to float within the frame.
This raises the question of whether or not sash joints should be glued. Traditionally, they never were, which is the important reason we can take them apart for repairs. If we glue them they cannot be taken apart for future repairs.
Glue may prevent moisture from migrating out of the joint, trapping moisture there leading to decay of the wood in the joint.
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