if you complete steps 2 and 3 in my post above, then the amount of wax to use becomes evident. Usually with a long board, you'll use 1/4 bar for base coat and 1/4 bar for top coat. I use same wax for both coats and use about one-half bar to wax the board.
Leave the wax on after surfing. You can leave wax on for 3 to 6 months. When you go surfing again you may have to add a little more wax. You'll know to add it if the existing wax is not sticky. If you have not surfed in a couple of weeks, it will likely be hard and not sticky. Add a thin layer just before hitting the water again.
Another way to extend the use of the wax on the board is to comb it or rough it with wet sand in the shallow water instead of adding more wax. After I've got a thick layer built up, say 3/8 inch, I don't add wax. I comb it. To use the comb, just rake it from nose to tail and diagonally from rail to rail. Lately, I've been doing this with only about 1/8 inch wax on the board. My buddy goes to ankle deep water, placed a big scoop of sand on the deck, and rubs it all around while the water is washing over the board.
You will know to re-wax the board when one of two things occur. One: when the wax offers no grip. You may find you can't hold onto the rails without your hands slipping off or your feet slip out from under you when trying to stand. When this happens, add wax or comb existing wax.
Two: when thick wax begins to fall off in sections. When this happens, lay board in sun for 20 to 30 minutes. Then scrape wax off with straight edge of comb or a plastic auto body filler spreader. Do not use metal object. You can use warm water, acetone, denatured alcohol and many other things to remove the very thin film of remaining wax. After removing wax, begin with numbered item 1 in my previous post.
1. don't wax board in sandy area. Don't place wax bar in sand. If you do these things, you will get sand in your wax. A little is OK. Too much is unsightly and unpleasant (skin scrap).
2. If you don't over wax the board, you'll pretty much always have wax on your board.
3. carry waxed deck away from your body or you will be covered in wax
4. if you use a wetsuit, the knees of your suit will get some wax caked on them. Don't worry about it.
5. select wax for the temperature water you surf in. The waxes are rated. In the old days, guys simply used things like Gulf Oil parrafin, which was a reasonable quality white wax. You really can use it today and will save a few pennies, but if you surf in truly cold water, it's worth the extra to get temp rated wax