Q.Turf Replacement
Hi there, I have an unhealthy 18 year old Bermuda lawn that was probably neglected for half that time, stays brown til May, does not recover well from damage, and has no topsoil layer below it. It sits on Georgia clay. Hard stuff when its dry. I’d like to replace it with Zoysia. One company is telling me to kill the Bermuda with herbicide, the other wants to rototill it 4 inches deep. I’m located in Atlanta area.

Certified GKH Gardening Expert
If you don't want the Bermudagrass coming up in your zoysia lawn, you need to kill it out first. Although zoysia is aggressive, so is Bermudagrass. Also, be sure to add a layer of topsoil to help establish the new grass. Here is an article about problems with zoysia, but it should do well in a warm area such as Atlanta.
https://www.gardeningknowhow.com/lawn-care/specific/zoysia/facts-about-zoysia-grass-zoysia-grass-problems.htm