“Therefore, the existing grass / lawn must be extremely sparse or you will have to bring in dirt and put it on top before laying the new sod. ... If you currently have weeds, they can grow through the new sod. And the ground cannot be too hard, or the roots will not penetrate, even if the roots are touching dirt / soil
Brown spots due to fungal problems usually show up as irregular patches. If the disease has been active for a while, the inside of the patch may recover, leaving a ring of dead grass around it. Extremely rainy or humid weather can encourage fungal outbreaks, as can lack of sunlight and poor air circulation.
When can I walk on my new lawn? New roots usually begin to appear on the underside of your turf within a few days after laying. To check just pick up a corner of the turf, if the roots have anchored then you can try walking on the lawn. This will normally be after 2-3 weeks.
Probably not. With proper care, including spiking, fertilising, and raking later on down the line, you can get a lawn that won't cause you any serious problems. But for the best results… Always remove old turf and put it safely to one side beforelaying new grass.