I've ordered an undermount sink for the kitchen. The worktops are
going to be granite, and the granite supplier suggested fitting the
sink to the base unit with MDF, such that the lip of the sink is the
same height as the top of the carcass.

Has anyone had any experience of MDF in this situation? Isn't it prone
to damage by water? Wouldn't treated chipboard (or even an off cut of
the old worktop) be better?

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Nigel M