1)If you're going to sharpen your skis, do this first, that way you wont get bits of metal in your fresh wax. Also, if you're going to fill any scratches or holes in your base with p-tex do this now.
2) USe a crappy iron or something and press your wax onto it so that it drips onto your skis, run a line of drips down the ski.
3)Then use the iron to spread the wax all over the ski, leave the iron on, its important to really get the melted wax everywhere. Don't hold the iron in one place, this can burn the wax and p-tex.
4)After you have spread the melted wax over the ski adequately (like buttering a piece of bread) let the wax dry for at least 20 minutes.
5)Then, use a plastic scraper (a stiff ruler will do) and scrape the excess wax of the ski, going from tip to tail. Hold the scraper at an angle towards you and draw the scraper towards yourself. Like so:
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6)Once you have scraped off the excess wax, use a ski brush or some brush with pretty stiff bristles and brush the ski down hard. This gets all the excess wax off the surface so that the only remaining wax is in the pores of the p-tex, you do not want any excess wax on the base of your ski. When brushing stops producing a lot of wax powder, then you're good to go.