Bricks, Masonry, Asphalt and Concrete - poured concrete problems

I have a concrete slab in the basement that we added floor heating to. I poured 11/16" of concrete on top of the existing slab to cover the electrical cables and will tile over the concrete. I mixed the concrete as per instructions with mason sand. I let the floor cure for 13 days, where the instructions stated 5 - 7 days for 3/4" thickness. When I was puuting up the drywall I noticed that the floor is very sandy and that I could scrape the flooring off by rubbing against the floor firmly with my finger in some areas. Do I have to redo do the floor or will it be sufficient when I lay down the floor tile?

Thanks in advance

Hi,

Hard to say which is the problem without a look.
I saw this problem in two situations: bad quality of the water (or water with too much sodium) or bad homogenization of the concrete.
In those situations, there was no solution, it had to be remade.

Best