First of all let me tell you about plastic primer..
You apply it before paint spray...
Order of the job is
1)repair bumper or new bumper
If new bumper then sand it with 1000-1200 wet sanding
And once it all becomes slightly rough apply plastic primer using gun or by piece of cloth..
Then use 1500 grit after it dries off with light hands
Then clean it with tac cloth or just clean it and dry any water particles..
2) apply filler putty wherever there are deep puddles.. Then sand it according to how much you applied using the 120-320-400 or 120-420 if you don't want to make the job too long with satisfying result..
3) apply Dico astar or Dico filler putty it is for fine tuning scratch marks if u don't want that details skip it.
4) if Bumper is not new no need of plastic primer. Only you need Dico astar to be sprayed on the areas where putty filler was used and then sand the whole bumper with 1500 grit after the astar is dried...
5) prepare paint by according to quantity.. Add thinner and paint in a can for mixing thinner should be added a little then mixing stick should be used to mix paint.. With the stick after mixing pull paint emulsion in little bit air and let it drip to measure how thick it is.. It should not be very viscous nor very thin like water.. Something in middle.
6) apply paint 2-3 coats
7) now prepare hardner lacquer mixture if the colour is metallic or pearlescent. If solid no need to spray lacquer hardner mixture.
8) take cup or anything u want for measuring..
Add lacquer, whatever amount you using. Extra lacquer will be later wasted so prepare according to need.
Then add small portion of thinner and prepare the lacquer, once its well. Mixed add half or slightly greater quantity then a quarter of lacquer quantity used...
Mix it well..
9)always check hardner lacquer mixture should not be viscous like honey and thin like water it should be somewhere in middle.
10) spray it with light hands at first coat and then later on with good hand movement speed release good hefty amount of lacquer hardner mixture and you'll get amazing shine..
Let it dry for a day or two. Then wet sand it with light hands with 2000 grit and apply cutting compound...
Warning
If you use more hardner the shine gets zero.
If you add too much lacquer shine gets a little dull and thick very grainy cost appears.
If you make it like
100g of lacquer then 30-50g of thinner and 4
35-50g of hardner will make a amazing mixture