Whats behind these soffits/fascia thats making the drilling so hard?!

[JM72]

Of all the DIY jobs I'm being beaten by a curtain rail! Trying to fit some brackets to an external wall and can't get the drill to go any further than an inch. I'm using a fairly new masonry bit and the hammer setting. Looking from the outside the soffit is only just above the window frame, and I'm trying to fix a good few inches above that.
I've tried using a small metal bit to see if I get any metal.filings (lintel?) but just get more masonry dust.
1950s ex council house.
Advice please.

 

[Mottie]

Probably a cement lintel with stones in it. I had the same in my house when I wanted to fit some brackets for a set of blinds. A hammer drill and new 6mm bits wouldn’t go in more than half an inch. In the end I got my mate to come round with his SDS drill. Went through it like a hot knife through butter. Took just seconds.

 

[Harry Bloomfield]

I've tried using a small metal bit to see if I get any metal.filings (lintel?) but just get more masonry dust.
1950s ex council house.
Advice please.

It is probably, a concrete lintel. Try using an sds drill, and bit, rather than an hammer drill.

 

[accelerator]

As others have said it's probably a cement lintel.

If you don't want to drill into it, consider a Twist to Fit roller blind instead of curtains.