Hot answers tagged windows
Option 1 - tapcon screws (or similar) into the solid parts of the block. Option 2 - stuff some wire mesh a few inches down the holes. Mix a very stiff mortar/concrete, place on top of the mesh, make a lovely smooth flat surface, and drop in some anchor bolts (probably overkill for a windowframe) or just screw the board in with tapcons or the like but ...
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