"Builders Flats" are generally low end paints that are highly pigmented and do not have much resin (the glue that holds the paint on the wall). Request your builder to use a quality primer such as our 370-25 VinylTek Drywall Primer. If it's too late for that, re-prime with our 605-13 Stainkilling Primer and finish with one of our 100% acrylic finishes.