In the Japanese sentence:

その箱は重すぎた。

I am told it means:

The box is too heavy.

But the the word 重い has the い missing. Is this normal when combining an i-adjective with another word such as すぎ？

Would その箱は重いすぎだ　mean the same thing?

質問を翻訳

You are suppossed to take away the final い of 形容詞 when you add suffix 過ぎ

可愛過ぎだ too cute
高過ぎだ too expensive
甘過ぎだ to sweet
辛過ぎだ too spicy

And for 形容動詞, just add 過ぎ

親切過ぎだ too kind/nice
綺麗過ぎだ too clean; too beautiful
元気過ぎだ too lively; energetic
にぎやか過ぎ too lively, busy (day, place)

重い過ぎだ isn't right :)