Question
Tom,
I bought a home in coastal SC in 2006.  The lawn is small, relatively shaded with only morning sun with live oak trees.  The home builder placed an irrigation system that as I found out now, basically over watered my yard of newly soded centipede grass.  
Now I also have found after placing plants that a majority of my yard is clay with poor drainage and my yard is a near mud hole now.  I do want to place sod down in the near future, I thought this time of St. Augustine.  I have corrected some of my drainage problems by placing some french drains.  My question is 1. Do I just spray my yard with weed killer and then a. hard rake or b. till my yard and restart anew.  Also should I obtain some sand to mix into the yard prior to laying new sod.
Thanks

Answer
Brandon:

It is hard to believe that clay exists on the coast, but possible.  You have dealt with the drainage. That is the first step.  Spraying will assure a purer stand on St. Augustine.  That type of sod should do better in the shade than centipede and tolerates damp conditions better.  It does like a richer soil and requires irrigation more than other summer grasses.

The next step will determine the soil structure.  Adding sand will physically alter it make up and provide some surface drainage.  If you wish to alter the soil biologically, add some compost with the sand.  Or add it without the sand.  Apply between two and three cubic yards per thousand square feet.  Bacteria will create a sounder soil structure over time and a richer nutrient cycle.  Doing both additives will be better if the clay is tight and does not drain well on its own.  High quality compost made thermophilically is antifungal.

Be sure to deal with any fungus which may have invaded due to overwatering or you will have the same problem next summer when temperatures favor fungal growth.

If you will add sand and/or compost, till it in to blend the materials together, making a new soil substrate for grass roots, not sheets of different soils.

Best wishes.