Simple past tense and past participle of waterproof.(verb)
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Use "waterproofed" in a sentence
"The bathing area is completely tiled and waterproofed, which is very important if you do not want water damage in your home."
"I always carry waterproofed strike anywhere matches."
"I carry waterproofed matches both in and out of screw cap case, regular stick matches in case, a knife/shave striker magnesium starter, and finally a DJEEP lighter, when I can find one."