Surf Fishing Line

How much mono "backing" do you put on your surf rod before transitioning to braid to fill spool up? and what size mono do you use?

I just tie the braid to the spool then put a piece of gray tape on the spool before I finish filling the spool. The tape will keep the braid from spinning on the spool.

Basically any mono at 20# or under is good for "spool grip". (Heavier mono gets somewhat wirey and won't grip well.) My experience is you only need a layer or two of line on the spool, so that's just a few feet. After you tie to the braid, unspool it all and rewind with good tension from the beginning. You want that mono under some tension to get the good grip on the spool.