Well all this isn't making me feel real comfortable with my future Mohawk (used) installation. How can we have Mohawk telling us to drill through the concrete and then we have Wej-it anchor mfg. saying they need a "bottom". Sounds to me if, down the road, the user had an "issue" these two mfg. are covering their asses. If you have drilled through the concrete, then Wej-it says ' we told you our product needs a bottom. If you don't drill through and you have an issue, then you have Mohawk saying 'we told you to drill all the way through the concrete'. Either way, YOU are wrong.