Crossword Genius

Condemn building material (5)

Ross

I believe the answer is:

slate

I'm a little stuck... Click here to teach me more about this clue!

This might be a double definition.

'condemn' is the first definition.
Although both the answer and definition are verbs in their base form, I can't understand how one could define the other.

'building material' is the second definition.
(slate is a kind of building material)

Can you help me to learn more?

(Other definitions for slate that I've seen before include "Stone used for roofing" , "Grey stone; tab" , "Roofing plate" , "Rubbish" , "rock used in building" .)

I've seen this clue in The Globe and Mail.
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