Our plain (non-ribbed) polyethylene have frames cut from solid ¾” polyethylene sheets so there are no joints to loosen up or come apart. The deckle is fitted with aluminum corners to hold the it in its proper position on the mould when in use. The heat-shrink polypropylene screening is attached to the mould frame using epoxy cement set in a keystone-shaped groove which mechanically locks it in.
Because of the materials used, with proper care these should last pretty much forever.
This shows the corner of the poly mould. The screening is held in a keystone-shaped groove using epoxy cement.