salt have a significant affect on the sand stone

Hi -

I have recently purchased my first home, a 1920's brick in Shaker Hts, OH - everything I've ever thought I wanted in a home, and more (I'm sure!!).  The front entry way has sandstone steps and landing, and during the winter months I put salt (the cheap stuff in a bag) on the steps and walkway to deter ice accumulation (trying to protect the mail person).  Does the salt have a significant affect on the sand stone or is it a natural occurance (errosion) that I am seeing now. I do see what appears to be sand, and I've noticed that there is now a gap between the threshold of the front door and the sandstone landing.  It looks as if there were some type of masonry caulking in place before. 

Any clues you can provide will surely be appreciated.

Kim in Shaker Heights