Do we really have to sand the table before we varnish it? Can't we just go over the old coat?

How to say “Do we really have to sand the table before we varnish it? Can't we just go over the old coat?” in Japanese

In Japanese

ニス塗(ぬ)る前(まえ)に、ほんとにテーブルに紙(かみ)やすりをかけなきゃだめ？古(ふる)いのの上(うえ)からそのまま塗(ぬ)っちゃえばよくない？

Nisu nuru mae ni, honto ni tēburu ni kamiyasuri o kakenakya dame? Furui no no ue kara sono mama nucchaeba yokunai?

Do we really have to sand the table before we varnish it? Can't we just go over the old coat? in other languages