I would seal this first with a good quality 3in1 psu (primer, sealer,undercoat). Then top with some gyprock topping compound. Then sand lightly with ...

I am a painter by trade and come across this problem often. I find the easiest way is with a long handled wallboard scraper, for the finer stuff use a ...

or you can buy a water based stain these days, or just used some burnt or dark umber tint that they will sell you at your hardware store. You will onl ...