Layers of rock used for roofing (6)

I believe the answer is:

slates

(Other definitions for slates that I've seen before include "Criticises severely using roof coverings" , "Thin layers of rock for roofing" , "Strongly criticise the roof tiles" , "Abuses with roof tiles?" , "Strongly criticises the roof tiles" .)

I've seen this clue in The Irish Times.

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