Old timers formula question

[boatsboatsboats]

Hi, I am currently treating my floor with old timers formula on my smoker craft restoration. I’ve seen people say that it needs a top coat of spar varnish. I’ve already soaked up four quarts of old timers formula for the floor on a 16 ft boat. What is the purpose of the top coat of spar varnish? Is it needed if I’m going to just carpet the floor anyway? And if so how long do I need to let it dry before I put the spar varnish on? Thanks!!