The original stain blocking primer. It"s an interior oil-based primer that tackles tough stains including water, smoke, tannin, grease, pet stains and more the original stain blocking primer. It"s an interior oil-based primer that tackles tough stains including water, smoke, tannin, grease, pet stains and more. the original stain blocking primer. It"s an interior oil-based primer that tackles tough stains including water, smoke, tannin, grease, pet stains and more.