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Plywood Coaster Warpage
This is what happens to an uncoated plywood coaster with fairly deep laser engraving after about half a year of use:

Warped plywood coaster – front The poor thing went all potato chip:

Warped plywood coaster – side I swapped it for one with polyurethane sealant, much like those fancier coasters with the same layout, and we’ll see if it survives longer …