What to do with my lawn?

I've had my house rebuilt and to save time and money, I employed a gardener person to do the landscaping. No gardens, only lawns. He carted in a lot of soil, spread it about, compacted it by walking on it, levelled it off, then put down a ready lawn type grass. Not the actual "Readylawn" but a similar product.
After a year of caring for it by watering etc, there's still the joints showing where it was rolled out, and in some places, the actual rolled turf is starting to lift. To me, it doesn't look as if the grass has rooted to the soil the chap brought in. Can anyone understand what I'm trying to say? Also, there are big groups of toadstools which I cant get rid of. Never had them before in my old lawn.
I've considered getting a garden fork, jumping on it to make holes in the lawn, and sprinkling some new grass seed on it. Will this help me? Advice will be welcomed. Can't check back until tomorrow. Thanks.

Sounds like the imported soil is 'dead', which is a situation we had when we filled a new raised bed with blacksoil purchased from a local contractor. It took years of digging in kitchen scraps, manure and other soil 'food' to get that bed to perform as well as two others.

The presence of fungal activity would also seem to indicate a fungally dominant soil thereby lacking bacterial activity which further confirms a lack of the right soil biology. This is prossibly due to the 'soil' being erroneously sourced/produced from wood related byproducts. Grasses/pasture (and vegetable growing) soil should be bacterially dominant.

Turf management is a pretty specialised branch of horticulture and you need to hunt out an expert in that respect.

Did you want ready lawn? Most contractor gardeners/landscapers prefer to hoe the ground and then they level it off and then either sow their grass seed or they lay the ready lawn. Ready lawn is a fairly expensive option. After a year of watering and fertiliser etc you would have had a perfect lawn if you had hoe'd the ground and sown seed. Our new lawn was fantastic six months after it was sown. The fact you have toadstools growing suggests your lawn needed lots of lime.

never heard of dead soil before in my almost 20 years of horticulture

@strathview. I can't do manual work any more so I called for quotes to do the work. While I didn't give any details on how the work should be done, the guy who eventually got the job, hadn't mentioned a ready lawn type finish. When the stuff 1st went down it looked good. I followed his instructions to the letter regarding watering, and when the 1st mow should be done. I asked about the joints and he said to water the area well, then push the joints together using my footwear. I did this, all to no avail. Every roll is still visible with some actually lifting at the corners. It came down to what I could afford and while there are a lot of outfits growing instant grass, the original growers in ChCh have a very expensive product which would have been way out of my price range.

He wasn't specialised in his field unfortunately and the only solution is going to be a costly one.
Get an "expert" in to assess and recommend a satisfactory remedy which I am guessing will be a complete strip back and start again.
Really brasses me off that so many inexperienced people get away with very poor practices.
Be sure if and when you get someone to right the job that they provide references and go have a look and talk to their references.
No references, no recommendation. simple.
I wish you the best of luck with this.

I'd suggest trying patience first, as it costs nothing.

Keep up the water so the turf doesn't dry out and die as the weather warms up. Mow it a bit longer than normal as that will also prevent it drying out as much.

The mushrooms will be from wood chips / bark etc that was in the compost that the turf was grown in. A nuisance, but they will gradually die off as all the wood material is broken down over time. I get a few in the lawn around my woodwork shop sometimes as a bit of sawdust and chips get lost in the grass. Grass is still good and healthy though, good organic layer has built up.

Any gaps that actually open up I'd just sprinkle some top soil and grass seed in the gap. Again give it time, the grass spreads and covers small defects.

Might be 6 months before it's a good established lawn, but that's the same for starting with seed, but with the advantage it looks "ok" (not perfect), and can be walked on already.

You are way ahead of a lawn I've been trying to save. Contractor just put down readylawn over clay, no real topsoil in some places. It's a hard wear situation, and the grass just wont hold up. Been having dig out the worse areas, fill with some actual topsoil and transplanted turf from a healthy lawn. (No budget to rip the whole mess out and start again, which is what it really needs.) You at least have topsoil under the turf, so it will probably "come right" over time.

Ok so your guy was sloppy with his workmanship but he was the right price for what you could afford. Go and buy some bags of potting mix and some grass seed and pour into the joins. Rake if need be. Fertilise and water.
Just for the record my fantastic lawn was oversown with more grass seed because we had hundreds of little birds( there were six different breeds of birds) that had a wonderful feast for a couple of weeks. It was just a case of throwing more grass seed at the lawn all the time. We were told to spray it for weeds (yes yes we said, never did though) just threw plenty of blood and bone at it and it is wonderfully lush. We had approx 1/2 acre sown out.