A French space, sturdy? That's too bad (11)

I believe the answer is:

unendurable

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'bad' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I don't see?

'a french space sturdy? that's too' is the wordplay.
'a french' becomes 'un' ('a' in French).
'space' becomes 'en' (in printing, a space as wide as a letter 'n').
'sturdy?' becomes 'durable' (I can't explain this - if you can you should believe this answer much more).
'that's too' says to put letters next to each other.
'un'+'en'+'durable'='UNENDURABLE'

Can you help me to learn more?

I've seen this clue in The Daily Express.

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