Superlative form of 'groaty'; most resembling grout, or containing the most grout among compared items.
From 'groat' or 'grout' plus superlative suffix '-iest'. Standard English superlative formation for adjectives with '-y' endings.
The groutiest mixture might seem like a failure, but stonemasons know that slightly over-grouted joints are actually more waterproof—a small excess is insurance against leaks.
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