Try to get the existing Tapcons out. Use a masonry drill bit to
clear/clean the holes. This next will take a bit of experimenting
Here are some choices:
If you can use the next size larger Tapcon, redrill with the
correct drill and install.
If the holes are already too wallowed out for the large diameter
Tapcons try this: Use either solid copper wire or roll solder (if
you use the copper, you can leave the insulation on). One piece
in the hole and install new Tapcon. If it is too tight, don't
take a chance on breaking off the Tapcon, you may need to drill a
slightly larger hole. You can drill the hole out to the point
that 2 pieces of coppr wire will fit.
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