I'm not sure what you read that made you so pesimistic. I will tell you that I certainly felt that way to start with. I live in the NC piedmont which stands for a deep vein of red heavy clay soil. White clay is even worse as it indicates that air can't get into the small particles and rust the iron to red. However it is plenty hard and slimy clay like when wet. We have the largest hand thrown pottery community here. Thirty miles south, the soil turns to sand and the interface is the brick capital of the country! I doesn't appear that anything except grass will grow in this soil. However, if ammended heavily with bulk, it does wonderfully as it holds water and nutrients extremely well. We are in the country. I found a cattleman who has cow manure/bedding piled up and mixed after being mucked out of the barns. I bought a dump truck load (I actually bought two and moved it multiple places later) and had a third to a half of it dumped in my ~25' x 35' garden and tilled it in. That could have been between 6 to 10 cu yds of black composted manure. That changed the texture of the soil and it is still there after 6+ years. Gas was much cheaper then and it cost me $60 for delivery and $50 for the manure. Would be much more now for delivery.

I'd get the soil test but I gonna go out on a limb and predict the % of organic matter is going to come back very low. You'll want to see %'s in the 4%-6% range and that's not easily done in a short period of time. Aerate and top dress is a great plan but you'll also need to mulch clippings back into the soil, leaves too. Fertilize with a product that will stimulate the microbes in the soil. Restore is a good product but there are others out there. Look for something that has a grain meal as part of the ingredient list. Soymeal, cornmeal, or even Alfalfameal. But be fully aware that it will take time. You can go the Scotts route and you'll get much faster results but the chemicals do nothing to address the fact that you have crappy soil. Chems don't build soil fertility so if you make that choice understand that you'll be using chemicals to fertilize and deal with weeds and pest/disease issues for as long as you own the property.

Is there anything I can do short of hauling away six inches of the stuff and buying a lot of topsoil to replace it? Nope. You could just wait for Mother Nature to break it down with rain and leave you with a nice brick hard surface of fine clay. Or you could make pottery out of it. :>)

Have to agree with gardengal, at least for me. If you were in Darwin I'd have a shot at the warm season grasses. But you need a cool season grass person who knows the names of grasses in your Ozzie speak. If you were in the US I'd say you could use a mix of fescue (Festuca arundinacea), rye (Lolium family), and Kentucky bluegrass (Poa pratensis). I'm fairly certain you have the same species available, but with different common names. You are coming into spring to do your seeding. For us in most of the US, that's a poor time to seed for two reasons. 1 is the heat, but looking at your climate, yours seems to be more like our Pacific Northwest (gardengal's home turf, so to speak). In other words, heat should not be a problem for you in the summer. The second reason is the summer weeds like to sprout in the spring. Again, not knowing what your summer weeds are, I can't comment beyond that. Our main summer weed problem is crabgrass (in the Digitaria family of grasses). I believe crabgrass to be a worldwide plant used as forage for livestock. If you folks have it, I'm so sorry. I would expect it in Darwin because it is a HOT season grass, well adapted to tropical climates. Sounds like you are starting fresh. With that in mind, here are my suggestions. These match with morpheuspa after my pre-preparations. Water the weeds lightly (5-10 minutes), 3x per day, every day for a week. The idea is to sprout as many weed seeds as possible. After a week spray everything with Round Up (glyphosate). Continue watering as before to sprout any weeds that take 2 weeks to germinate. Spray with RU again. The whole idea here is to sprout all the weeds before you put your favorite seed down. If you don't do these steps, those seeds will sprout along with your expensive grass seed. Crabgrass, for example, sprouts first in just a few days, which makes it look like you're a seeding genius, when in fact, your lawn will be all crabgrass by mid summer. Rake up all the dead stuff. Evaluate what you have left as far as soil profile. If you have high spots, scrape those off with a hoe and fill the low spots. If you still have low spots, fill those with topsoil and crush any clods into dust. Water the topsoil to settle it and look for new or remaining low spots to fill. Fill any new or remaining low spots and water again. Repeat step 8 until you are entirely happy. What you are doing is setting up the turf profile. You can make it as smooth as a putting green, and the smoother you make it, the (much) happier you'll be later on. There is nothing less fun than mowing a bumpy lawn...for years and years. Now you are ready for morpheus' step 2. I'm with him on the install. I'm just a little more persnickety on the soil prep. As morph mentioned, don't think of dense clay as a handicap. It could very well be you have no clay at all. Don't be shocked. In the US about 90% of people fretting over clay soil have no clay once they get a good soil test done. Are there any brick making factories near you? If not then you might have a salt imbalance instead of clay. Morph suggest a soil test from Logan Labs in Ohio. I'm relatively certain they test soils from around the world. I know the big private test lab in Texas does. The cost will be $20 US plus postage. The benefit is that morph is extremely familiar with their tests and will give you about $200 of free advice if you post the results here. They email the results, so it's pretty fast. The other benefit of the LL test is they do a lot more tests than a typical university test lab for the low low price of $20. You could get all the LL tests from a university, but the cost would be a lot more than $20. Their test will tell whether you have clay or a salt imbalance. It will provide organic content (I'm guessing yours is around zero if it's cracked open) and soil pH. They also provide micronutrient balances. It's a great test. Wherever you get your test, do not use gypsum or any calcium until you have a test that tells you what kind of calcium and how much. The LL test will tell you - or morph will tell you based on his reading from the results. He'll tell you what products to use, when, how much, how often, and he usually explains why or why not along the way. You also need to decide if you are going to water with a hose and surface sprinkler or install a buried sprinkler system. NOW is the time to install if you're going that route. Now that I've written all this stuff, I reread your initial post. New house build. Did you have a landscaper do final grading around the house??? This is critical as I've spent a lot of time under the assumption that your yard is already profiled for drainage. If it is not and still looks like a construction site, then you need a landscaper to bring in, or remove, enough topsoil to give you a soil profile that drains water away from all the buildings and away from any neighbors. Can you post a picture or two taken from the street or from 20 meters away from the house. Here is a picture of a landscaper doing final grading in a level neighborhood. Also it doesn't hurt to give us the name of your town/city/village. If your landscaper is going to bring in new soil, don't get the soil test until after he's finished. He does not need to amend it going in. Unless it is really junk soil, it can be fixed with surface applications and by growing stuff in it. Weeds might be ugly, but they do provide roots in the soil which are organic.