Treating & finishing new spotted gum decks

Recently paid a lot of money for professional to paint exterior of our 2 story home. Now a chippy is about to totally replace both top & bottom decks in wide spotted gum boards (upper deck is partially exposed to weather). Getting conflicting advice from builders -v- paintshop & painters. Builder saying don't need to use Prep / Revivor & sand - just leave finished deck for 2 weeks then coat with Intergrain Ultradeck. Paint shop says must use Prep, then Revivor prior to applying Ultradeck with light sanding in between. Painter agrees we must do as paint store says but adds, if you do this after deck built, the drip/splash (especially from top deck splashing/dripping down to bottom) will damage new paint on house & recommends doing full recommended treatments on timber prior to deck build. But! Builder says if timber is laid out in yard (& sun) to treat it, it will warp, even within 20 minutes of being in the sun. What would u advise?