Question about sanding

Do What Oldvart Said. This Is The Only Way To Do It. My Brother And Dad Has About 70 Years Between Them In This Business, They Know What There Doing. Keep Adding That Scratch Coat Till The Blocking Is Done. 400 In The End Is As Far As You Should Go. Don't Forget The Paint Needs To Be Able To Bite On To Somthing. To Smoth Is No Good Till Your Paint Is On. Then Do A Sand And Buff.