Unable to drill into window lintel - what have I got wrong?

Question

I'm new to DIY so forgive my lack of knowledge! Just bought a house and have ordered blinds to fit inside the window recesses. Fitting them involves drilling into the top of the window recess to mount two brackets.

I have a percussion drill (this one) and since it didn't come with masonry bits, I purchased a Bosch drill bit set (this one). Using the 6mm masonry bit from this set (it has the distinctive "hammer-head" look), I attempted to drill a 5cm hole straight up into the lintel and after a few millimeters of soft plaster, I hit either concrete or stone and have been unable to drill any further than 1cm in with around 10 minutes of drilling slowly. Having read around, if the hole takes more than 30 seconds to drill then something's not right.

As far as I know, I'm using the correct drill bit (which hasn't worn although got hot) albeit from a relatively cheap set and I do have the drill set to percussion mode and rotating the bit clockwise. The drill claims to be able to drill holes up to 13mm wide in concrete and so the only things I can think of are that the drill or bit aren't up to the task (though the bit is still intact) or whatever I'm drilling through isn't concrete. I'm 100% certain that the lintel above the window is not wood, as inspecting the hole reveals a hard grey material like stone or concrete.

I guess my question is: is my equipment not up to the task, whether this is because the equipment is cheap or because the equipment I have can't be used to drill into stone?

For information, the house is a former council house built in the 1960's.

Thanks in advance!

Answer 1

Plate steel has been used to support lintels when the span is over some distance. That detail is obsolete now un the US but I'm not sure when they stopped doing it. Now-days its plenty of re-bar and in lintels it is often caged. Rebar should not be closer that two inches (5cm) to the edge of the concrete. Maybe there is an engineered steel bracket embedded in the lintel. Either way, you are likely running into steel.

They sell rebar eater bits, assuming that is what you hit, they can cut through steel but if you hit the bar dead on then even a rebar eater is going to have some work do grind through it. Only use them on rotary, percussion destroys the carbide teeth on them. Maybe you can move your hole a little? Maybe use a smaller inexpensive steel twist drill you don't mind throwing away in the same hole and observe chips that come out, looks like steel?