Mortar under padstone thickness

[Mywristhurts76]

I'm in the process of installing padstones for a universal beam. However, I've cut out the existing brickwork incorrectly and it will result in a 20 mm mortar bed thickness to raise the beam to the correct level.

I understand 20 mm is twice the desirable depth but ultimately, will it be okay? If not, what are my options? Would it be preferable to fit a 10 mm spacer between the padstone and beam rather than a 20 mm mortar thickness?

Thank you in advance.

 

[catlad]

a good thick slate will do.

 

[Mywristhurts76]

Thank you. Do you mean as a packer between the padstone and beam instead of steel?