I have inserted a steel beam under a broken floor,
and chiseled under the joists so I can get it in,
but there are irregular gaps in between of about half an inch and less.
The joists will sit on the metal beam.

How shall I fill the gap?
Some bits of slate and readymix cement?
or car body filler?
But mightnt they crumble as I adjust things?

Something a bit flexible like HardAsNails?

Or lime mortar?

It's only holding up a floor and a bath,
so it doesnt have to be super strong,
but i want it to last a hundred years.

thanks

[george]