This product is designed to be used in stain blocking interior and exterior primers. It provides excellent tannin and marker stain blocking in zinc oxide-containing and zinc oxide-free formulations, excellent sandability to allow primers to be be quickly topcoated, excellent alkaki resistance minimizing efflorescence, and good adhesion to a variety of substrates including alkyds, wood, masonry, aluminum and steel. The product also has very good enamel holdout properties and can be coalesced with non-volatile plasticisers to formulate primers with <5g/l VOC and is made without APEO-containing surfactants.