Any recommendations for coating/sealing cellar walls? I'd like to tidy up the
appearance, and avoid the mess that builds up.

The cellar has high humidity (always 70%+), and water will form if anything is
left up against the floor/walls, but is basically dry. What looks to be
masonry paint has stuck where the other side of the wall is open to air, but
where there's soil the other side it's crumbled away. The main cellar walls
are made of what look like stone rubble held in place with coarse mortar.

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Cheers, Rob