I decided to tape and joint T/E plasterboard instead of plastering for the first time. What type of sealer do I need to seal the walls before painting? The Siniat joint filler will be more porous than the plasterboard surface. I've seen people mention using a mist coat of watered down emulsion, does that work? Is this No Nonsense Primer & Undercoat 2.5Ltr the correct stuff? Thanks.