Suggest you start with a smaller bit than you think is necessary,
and also try initially without hammer action in case you found
a soft bit of wall like a mortar joint. (Don't persist without
hammer action if the wall is hard, as you'll overheat the bit.)
In some types of wall, the hole easily ends up wider than the
bit, and your smaller bit might actually have created the right
size hole. However, if the hole needs widening, you can now do
this with the right bit, and hammer action won't be required,
so the hole will be a cleaner cut and stronger.
In airated thermal concrete blocks, never use hammer action
(it causes significant damage in the structure around the hole),
and even masonary bits are not a good idea (once you've gone
through the plaster). For these, you want an accurate parallel
sided hole. I use old HSS bits, but don't expect the bits to
last. Again, the two bit method can work very well.
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