Jerry, you should more completely describe the repair you need to make so people can make recommendations.

Mason and Mortar mixes are typically used to "stick" things together, like block and brick. Or used to repair such joints.

To fill in a hole from moving pipes etc then regular concrete. Mortar or masonary is not for floors. It is for brick laying.

If you are trying to patch a bad surface of a floor then none of those are for that job.

Thanks, I want to fill a gap between a floating slab that is in very good shape and the cement block wall that is also in very good shape. There are no water problems, but my Radon is a bit high. I figure filling the gap will reduce the inflow of Radon, I need to get the count down only a couple of points.

Again, there is no water problem. The walls have a modern footing and "French Drain" with a gravity feed "sump" line (comes out down the hill below the footing level).