Building material, but it could be out of date

I believe the answer is:

stone

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'building material' is the definition.
(I know that stone is a type of building material)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for stone that I've seen before include "Boulder" , "14 lb" , "that one will 26d at 8a [FLING at HIGHLAND GAMES]" , "Olive pip" , "Rock; hard seed" .)

I've seen this clue in The Irish Independent.

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