Repair Solutions – Best Compound to Fill Drilled Holes in Cinder Block

With stucco the wall is two thin for tapcon screws, Since you already have a hole I think your best bet is a molly bolt or toggle that expands once inside the wall fill the hole with calking so no moisture or bugs can find thier way in.

The block will be much more durable and solid if the webs (cavities) are filled with concrete. I'm assuming the blocks are being set in mortar? and not dry set? Mortar can be used as a fill and since the height isn't much you shouldn't see any compromise in strength.

You can float the voids level, but a neater look would be to cap the top blocks with an appropriate and preferred material such as granite.