Roller blind installation

[wm460]

I am in the process of installing blinds in my house all was going well until I was drilling through the render and hit air.
What is the best way to rectify this problem?
Only one out of four was successful.

The walls are rendered brick.


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[droog]

What is the best way to rectify this problem?

There really is only one way to rectify the problem, drill where there is supporting structure.
Where that location is depends on the construction ! You say rendered brick but bricks come in clay or concrete, some are solid or may have a few holes or even honeycomb construction.

If the supporting structure does not exist where required for the blinds then I would install a timber batten across the top of the window / door opening to attach the blind too, mounting the batten where there is support structure in the wall for it.