Hi Juan,
Sorry for the time between replying. Our files are mastered to 18mm, 15mm 12mm and 6mm BirchPly and WISA Multiwall, depending on the design. In this case the Olivia is 18mm but as we haven't tested another ply apart from birch we'd be unsure of the result.
Key thing is if you think ash plywood is as tough and structurally stable as birch ply so it might be an option and if you can source 18mm ash ply that will match the tolerances, but again we haven't tested it so can't promise it will work!
We'd love to see how you get on with a picture in the
workshop section on our website. It would definitely help for future wood variations!
Thanks,
Jack