Surfacing material one omitted from column (7)

I believe the answer is:

plaster

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

'surfacing material' is the definition.
'plaster' can be an answer for 'material' (plaster is a kind of material). I am not sure about the 'surfacing' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for plaster that I've seen before include "Smear" , "Spread" , "Smooth mixture to cover walls" , "Sticky bandage" , "Stucco" .)

I've seen this clue in The Times.

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