I have a low garden wall of tapestry bricks. This style of brick has vertical marks scratched into the clay surface before firing to give a different finish. Behind the wall is a garden with soil against the brickwork. On the exposed side is a hard white deposit which fill the tapestry marks. It cannot be removed by wire brushing or waterblasting. I suspect it is salts, a lime deposit or silica, the results of soil, moisture and nature working on one side of the bricks and forcing the product through to the exposed side. It is not too unsightly but I would like to remove the deposit to have a clean look to the brickwork. Any ideas?