How deep in the soil do the roots of weeds grow? Would getting rid of top 3 inches of lawn and putting in triple mix and sod get rid of weeds? (Our lawn has more weeds than grass).
Plants with only three inches of root depth are not going to survive hot and dry weather in the wild (i.e. not growing in lawns watered by sprinkler systems), and the common feature of "weeds" is that they survive better than most other plants.
Weeds with tap roots will be much deeper than 3 inches. For example dandelion roots typically go down 6 to 18 inches, but can grow as deep as 10 feet or more!