To be honest I had never heard of any one top dressing their lawn until after my wife and I decided to get into lawn care. As I said in the previous post it is very labor intensive and with just my wife and I, it can take a couple of days depending on the size of the lawn.
Before beginning the amount of topsoil needed has to be calculated it takes a LOT of topsoil to add 1/4 of an inch to an entire lawn so you will be buying it in bulk. Top Dressing should be done during an active grass growing period. It is a little stressful on the existing grass so you want it to have time to recover before it goes dormant.
After calculating how much topsoil is needed the next step is to watch the weather reports closely. Ideally you want about a 5 day period without rain in my opinion. This is to have the topsoil that is being delivered not be too wet, you want dirt not mud. Then you want a couple of days to do the actual work.
Lets say the dirt is being delivered on a Wednesday at 9AM. You can either mow the yard on Tuesday or early Wednesday, I prefer Tuesday as there are other preparations to be made for the delivery so it could be a time crunch to try to mow on Wednesday. You want the yard freshly mowed, you won't want to mow for a few days after the topsoil is added so it can settle and not be blown around by the lawnmower.
When your topsoil arrives you will need a wheelbarrow, shovel, metal rake and something to help even the topsoil which could be a gravel leveler
or a simple drag harrow
A commercial drag harrow has an area to add weight and some have hooks on one side, we don't need to be that rough on the existing ground and a plain 4 X 10 piece of chain link fence material works quite well.
You will use the wheelbarrow to place the topsoil in small piles around the work area. The piles should be small so that they can be easily spread out, a full wheelbarrow will give you four or five small piles. I use my riding lawn mower to drive over the pile, the mowing deck will start to spread the top soil and the harrow finishes spreading it out. Two or three passes in different directions does a nice job and the rake can be used upside down to help if more attention is needed in some spots.
The harrow will leave some grass poking through the topsoil and deposit more of it in low spots. Depending on how many low spots your yard has (mine has a lot of uneven areas) the job may look very patchy for a couple of days until the grass recovers. After you are finished, if you plan to over seed the yard it is a good time to do that and then water the grass thoroughly to help settle the new topsoil. After a couple of days the grass should be pretty much standing up again and the topsoil will have settled in between the blades of grass. Water it again if needed. If the lawn had deep depressions in it such as my dogs seem to love to dig, those spots could take several days for the grass to get back through it. The more vigorously the grass was growing when the Top Dressing was done the faster it will grow back through. Grass that is just coming into or out of dormancy will take longer.
One Cautionary Note : When you buy topsoil in bulk, you WILL get weed seeds in it. Count on it and plan for it!!
I recommend that if you choose to Top Dress you do it in the early Fall before the lawn goes dormant. Then in the Spring apply a Weed and Feed type material so the lawn will look good for the summer.