Hello all
I have decided to install grass.
In soil preparation, is it ok to layer lawn dressing and phosphate before the actual grass laying?
Thank you

What do you consider lawn "dressing"? Basalmic Vinegarette? Raspberry Honey Mustard?

I'm sorry, I've just never heard it phrased that what before. Yes, of course do all the prep work prior to laying it down.

You don't say where in the world you live. I assume you mean you are laying sod. Grass, sod, lawn, are not interchangeable terms to me.

If you are going to make yourself a lawn, prepare in advance. Carry out an irrigation system, delimit the territory, buy equipment.
From my own experience, I say, prepare in advance

You don't want to add (P) fertilizer unless you have a soil lab report telling you to. I assume you are in Australia and it's growing Season. The # 1 grass killing fertilizer is phosphorus when added to an area that has
high amounts of phosphorus. It will turn the grass yellow every year for about 5 years after poisoning the lawn with phosphorus just one time. The most used fertilizer for lawns is (N) and that won't be needed until the grass is growing. For starting the best lawn,-- spent about $30 and get a soil test with recommendations and save yourself a big headache. good luck