Either buy those big white emergency candles or just get paraffin wax. It works pretty good unless the concrete is super chunky, In which case just hope for the best. Having something to melt the wax on to the ledge helps too.
def clear coat it with something then put the wax on. also it would help if the skis you used had no edges where you would be grinding. but a big candle would probably work but put a layer of skate wax on top to make it extra slidy
"What I care about is being able to click into my skis for the rest of my life. I care about being on top of the mountains with my best friends. If I'm on my skis, I've got a big smile on my face. And I want to keep it that way." T-Hall http://vimeo.com/thenewsolution
if it is really rough buy a "rub brick" from Lowes and smooth it out a little. if u want it real slick use spray lacquer like mentioned above, and then wax. those jesus candles work good if u break em outa the glass.
I usually just make skate wax but it works for skiing .. take a candle break it up, put it in a tin can (like a used sauce can or something) boil soome water in a pot and put the tin can full of wax in it, but don't let the top of the tin can go underwater, then stir it with a Popsicle stick until the wax is mealted, after that take WD-40 and put it in the melted wax (the more WD-40 the more slippery the way will be), stir for about 2 minutes and then take the tin can out of the pot of boiling water and put the entire can of melted wax( with the WD-40 mixed inside) into your fridge to harden. Then once it's solid again take it out of the fridge and bread open the sides of the tin can and you will have a nice little block of wax ski/skate wax that works great for waxing concrete!
either melt a TON of wax (surf wax, candles, snow wax, paraffin wax) over the area you wanna slide or use a few refilled gallon jugs of water and that'll do it. just make sure to get a lot of water frozen then try and level it out a little bit. paint scrapers work for that.
wd40 is a water displacer, common to popular belief its really not a lubricant. I dont think it will help you much waxing a frozen concrete ledge. The only use for wd40 I could find in this situation would be to break up the ice frozen to the ledge before rub bricking it.
i am a bit unsure about the use of surf wax. surf wax always has a little bit of give to it which helps with the grip.. and would be very unhelpful when trying to slide it on skis. but if you did go for it, definitely get the cold california low temperature stuff, or else you'll be scraping wax off the bottom of your skis for days.