That’s a good description of efflorescence. The white powder is actually a kind of salt from inside the brick, block or mortar. When water from rain or other sources penetrates the masonry, it dissolves these salts. Sometimes rain will carry more salts into the masonry. As the force of evaporation pulls the moisture back out to the surface, the moisture carries the dissolved salts with it. Once on the surface, the moisture evaporates, leaving the dissolved salts behind. They build up into those deposits. Washing with a garden hose won’t help, because it puts more water into the masonry. To control efflorescence, first check that water isn’t getting in through failed joints, cracks or other defects. Fix it, if that’s the case. Once you’re sure the masonry is sound, let it dry thoroughly. Then give it a good cleaning. Start by testing Sure Klean® Light Duty Concrete Cleaner. This is usually effective for red brick and gray mortar. For colored mortars and light- or unusually colored brick, test with Sure Klean® Vana Trol®. Once the brick is cleaned, let it dry thoroughly. Then apply Sure Klean® Weather Seal Siloxane PD. This breathable, penetrating water repellent will protect your brick storefront from efflorescence, mold and mildew, freeze/thaw cycles and a host of other water-related problems.