Fiberglass Stairs Flexing

[tz0zk6]

My concrete installer failed to push enugh concrete up under he lip of the 8 foot fiberglass stair unit in my inground pool. Now if you step in the center of the top edge (top of first step level w/concrete) the fiberglass will flex about 1/4", afraid that it will eventually crack. Does anyone know of a trick to get support under the step without taking the concrete back out? Was thinking of drilling small holes into the concrete on an angle towards the stairs and then injecting concrete or expanding foam up under the steps until the void is filled. Would this work?

[Jobo]

I think that using expanding foam would be ideal. It cures with moisture and will not rot or break down.

Injecting concrete would require a large hole and no way to get rid of the trapped air under the step.