Clean the Surface

• If you're not going to etch the porcelain, it's that much more important that the surface of the tub be as clean as possible. Abrasive cleansing powder is usually a bad idea for porcelain tubs, but this time is the one exception. Put some of the powder on a sponge, add just enough water to make a thick paste, and start scrubbing. Scrub it in from the top, working your way down, using small, fast motions. Get the tub as clean as you can, then rinse thoroughly with warm water several times to remove any leftover grit.
  
  

Prepare the Room

• Use a razor knife to cut out any caulk around the tub. Remove or tape off the overflow plate and drain cover. Put thick plastic tarping over all nearby walls, taping them with masking tape alongside the tub. Lay more plastic on the floor around the tub, taping it down. If there's a window, put a fan in it, blowing out, to ventilate the room (don't blow the fan in, as it will interfere with the paint sprayer.). Put on long sleeves, rubber gloves and particle mask.
  
  

Apply the Primer and Paint

• Fill your paint sprayer with epoxy primer, made for porcelain. Make sure it's formulated so that it doesn't require acid etching before priming (some do). The primer should be a dark color, so you can see exactly how it's going on in the white tub. Set the sprayer on very fine light mist, start painting from the top of the top, and keep the wand moving so there are no drips. Plan on at least two very thin coats of primer, allowing 30 minutes between coats for drying. Apply the top layers of white polyurethane paint in the same manner, except plan on using four to six coats, again keeping them very thin. Let the paint set for two days before using the tub.