what salt to use on a untreated wood ramp?

There are a number of different ice-melting chemicals available, "rock salt" or sodium chloride being just one (and actually a poor choice). For temps below 15 F, get a product that includes magnesium chloride or calcium chloride, MgCl or CaCl2 hopefully listed on the bag. Best practice is to use a shovel and broom to routinely clear what you can, then add a light sprinkling of these products - less than what you've used before with the most common stuff. Calcium chloride will melt ice down to around -20 F ,at which point it's dangerous to be outside anyway. Keep a container of sand handy too, and toss a little down for traction.

The goal is to make it through to Spring with nobody falling and getting hurt. A little cosmetic damage to the surface of the wood is trivial compared to a broken bone. Have a happy new year

Nothing really just cover it and treat it when the weather gets better cover it with a big tarp is about all you can do and say a good prayer that it lasts through the winter or just shovel it off each time you want to use it.

You should have use treated in the first place. Now if you use that safe salt its not going to work as well and its going to track all into your house.Use good salt..falling on a ramp is bad biz..Good Luck

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Use sand or kitty litter instead.