On a sidenote, I do mulch all my grass clippings and I mow over all the oak & maple leaves that fall on my lawn every year, so maybe that adds some soil over time as it decays as well?

(What exactly is topsoil?)

I think you are fine adding compost. As long as you have 6-12" of good decent topsoil, there is no need to rototill. Rototilling actually bbrings weed seeds back to the surface.

If your soil is compacted, you can aerate and then spread compost, 1/4" depth, over the yard, at 1 cu yard per 1000 sq feet.

Heh, what is 'good decent topsoil'? I live in Rockland County where clay is the norm...I would say maybe I have 3-5" nice feeling soil to my fingers, but 9-12", no way, it's all 100% compacted that far down. So maybe I should rototill, sow the grass heavily and hope that the weed seeds brought up won't germinate in the fall and the grass will have established itself by the time the weed wants to reach sunlight in the spring/summer.

I've aerated the past 2 years though so at least the top 3-5" should be somewhat ok and I guess topdressing compost every year or 2 from now on will help sustain it going forward.

Clay is a great soil if you keep enough organic matter in it. In other words, you don't need to add _soil_ if you add enough compost (mulching helps do that without hauling it in). Also, if you keep adding organic matter and aerating the hard pan below will eventually get broken up.

Whether to till or not is a whole 'nother question that you will find alot of debate pro and con on if you do a search. If your action the last couple of years have it loosened up down to five inches already, tilling probably isn't going to be a great help any way. But, it can get more OM into the soil faster. Mostly a matter of personal preference once you see the pros and cons.

Your use of compost is improving your soil every year. For additional improvement, consider switching to organic fertilizers in order to better feed the micro-organisms aerating and conditioning your soil. Bill Hill

Here is a link that might be useful: organic Lawn FAQ

"(What exactly is topsoil?)"

That's a topic that gets debated (sometimes heatedly) on the Soil, Compost, Mulch forum pretty regularly. I don't think there are any regulations around what can be labeled topsoil, so if you buy topsoil, you never know what you're getting. I bought a truckload of "topsoil" once, and it seemed to be a mixture of the native clay, shredded trees and pea gravel. I bought a bag of "topsoil" at a big box store, and it looked more or less like finished compost.

As has already been pointed out, you've been steadily improving your clay and it will continue to improve if you continue adding compost, grass clippings and shredded leaves, it'll continue to improve. And if you use organic fertilizers, it'll improve more.

Tilling would incorporate the OM deeper faster. The problem with tilling is that it is difficult to get the soil level after tilling. If you grade it (probably best to have it professionally graded), that will ensure it is level when it it graded. But if you've tilled in lots of OM, it is likely to break down unevenly, and you could end up with an uneven lawn.

I have clay type soil too. It works great because it holds the nutrients but you need to water it on/off because it absorbs water slowly. Also it needs aeration relatively often because of the compaction.

Roto-till if you want, but be aware of problems with leveling and weed issues, and face the numbers. To do any good you are going to have to add at least 2 full inches of compost tilled down 6-inches to even touch OM content. Then after one-year it has decomposed leaving you right where you were to begin with.

Ok, well, I really don't need to rototill if it's not necessary. Today I spread about 1/4" compost on the areas of my front lawn that I killed off and raked....

But my concern is that if I just leave it as-is, run the aerator over the whole lawn a few times (cris-cross), then seed & lime & starter fertilize.....it just seems strange to have the seed start growing in the OM and then about 1" down, the grass root will all of a sudden hit clay w/o OM. So shouldn't I maybe rototill the compost just about 1-2" into the top layer of soil to mix things up a bit before I run the aerator over everything?

Need answers asap if possible, going to try to fit everything in tomorrow morning/early afternoon!

Tnx!

You have received advice here from some very knowledgeable persons. And you still want to use the rototiller ???, There is absolutely no need to till in ¼ inch of compost. I am no expert but I have often read not to rototill an existing lawn while renovating. Bill Hill

Ok, well, I really don't need to rototill if it's not necessary. Today I spread about 1/4" compost on the areas of my front lawn that I killed off and raked....
But my concern is that if I just leave it as-is, run the aerator over the whole lawn a few times (cris-cross), then seed & lime & starter fertilize.....

You have done things in the wrong order.

The lime should have gone down some time ago as to give it some time to do its work.

You aerate, seed, fertilze, then topdress with whatever, compost in your case. Not the other way around.

I put lime down last year, tons of it. I was only going to add more lime this year because I was told that the compost, if not limed, will lead to lots of lawn mushrooms next year as compost is more on the acidic side...(a guy said that happened to him while I as getting the compost).

I guess I'll just make do with what I've done already and just aerate it well, forgot rototilling, and maybe topdress very lightly (sprinkle by hand) on top of the seed with whatever compost I have left over.