Use a brass brush to replace some "structure" into your base.
Try before waxing, it helps the wax penetrate the base and thus last longer.
Racers should also use a brass brush as the first brush after scraping
Dougie Crawford (World Cup Racer) says
"Use before waxing to clean out any dirt picked up over the day and get out any leftover wax this means that more new wax will go into the ski.
I also use a brass brush as first brush after scraping, it gets lots of the wax out of the structure so skis run better.
For training I only do a few strokes with this as I want to leave some wax in the ski as I'm going to do several runs on a pair of skis, this is what I would suggest for recreational skiers. For racing I brush for several minutes with the brass brush before using other brushes."