Posted: 09/03/2014 at 11:13
You may well have overfed the lawn from what you say. Over feeding produces lots of lush growth and weak root growth.
The wet conditions we have had will have weakened the roots.
Laying a new lawn on top of what was basically a building site is asking for trouble as the soil will contain too much building waste.
Builders aren't gardeners usually.
I would give it a few weeks, especially now the weather has improved, but if the lawn doesn't recover, I'd be tempted to start again.
In the how to section there are plenty of instructions on getting a new lawn started.
You may have to dig the whole lot and remove the rubble, and improve the soil at the same time.
There's plenty of advice available here, so you will get plenty of help.