Kate wrote:
I hope I am explaining this properly.

My front door has a metal plate installed underneath the door, that is
mounted to the floor. I call it the threshold, and I hope that is the
proper term for it. Anyway, last year I mixed some powdered concrete
mix, and pushed it in underneath the threshold.

Now the cement is cracking, and I removed it in hopes of putting
something else besides concrete underneath the threshold plate. This is
the plate everyone walks on when entering my home.

Does anyone have some ideas for me?

Many thanks.

Kate

First, are you trying to secure the threshold with the concrete, or
just fill in the gap?

If you are trying to secure the threshold, that method is not very
good. I have found that drilling a hole into the concrete floor (if
that is the situation) with a masonry bit and filling that hole with
wooden dowel rod is the best way. Cut off the dowel rod flush with the
floor and drill a hole for the screws used to secure the threshold into
it. The dowel rod will expand outward once the screws are installed
holding down the threshold.

If your problem is filling a gap and not one of securing the threshold,
I found cutting wood the size of the threshold to fill the gap is very
effective. Plywood comes in various sizes and often solves the problem.