Fluid pressure with tiles? Use a sealant for this (13)

I believe the answer is:

waterproofing

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'use a sealant for this' is the definition.
The definition suggests a singular noun which matches the answer.

'fluid pressure with tiles?' is the wordplay.
'fluid' becomes 'water' (water is a kind of fluid).
'pressure' becomes 'p' (scientific abbreviation).
'with' means one lot of letters go next to another.
'tiles?' becomes 'roofing' (roof tiles).
'water'+'p'+'roofing'='WATERPROOFING'

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I've seen this clue in The Times.

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