On Sun, 21 Nov 2010 08:54:43 -0500, "Robert Green"
wrote:

No "layers" Its 5 yrs old, poured all at once, about 4-5" thick

Well, *something's* different about the layers. Are you using the throwaway
bits that often accompany the package of Tapcons? I know people who say the
Tapcon bits are junk compared to the much more expensive Bosch bits. What
diameter are you using? Do you have any different sized bits? Have you
considered using the .22 powered ramset fasteners? Since you know something
about the initial pour, do you know the composition of the mix? Have you
tried irrigating the troublesome holes with water to cool the bit and clear
away the dust?

My best advice would be to get a different bit and use the slowest speed
possible while keeping a stream of water, even if only from a squirt bottle,
on the drill bit.

HTH

All good ideas. I had a similar bad experience with TAPCON bits on my
poured foundation wall.
Thinks that's when I bought my hammer drill.
Some concrete is *really* hard to get through.
I decided then that if I did it often I'd buy a ramset, although those
aren't foolproof either for stuff that shatters.
My foundation wall is so hard I expect a ramset would have cratered
it.
I've decided not to hang anything else on it.
For the sole plate the OP is doing I recommend just getting a couple
good holes drilled per 8 foot plate and gluing it down.
If there's wrestling matches going on down there the wrestlers will go
through the wall before they knock the sole plate loose.

--Vic