1. A substance, especially a cement of clay or the like, used to close up a hole: Sam read that lute could be used for packing a joint or coating a porous surface to produce imperviousness to gas or liquid.

Lute is a soft, earthy packing mixture used for closing or sealing apertures, joints, or porous surfaces in order to make them resistant to liquids or gases.
2. A packing ring, as of rubber: A lute was necessary to seal the fruit jar.

To cover or to seal something: Jane luted the cracks and the porous surface in the plate