Sulphur problem in broikc chimney

[stokepotter]

Hi, We have a brick chimney that has for many years been used for a coal fire. The bricks are now porous and there has been a chimney pot leak which has let in water and now caused the bricks to ouse out wet sulphur deposits. Any idea what I can use to seal the bricks on the chimney wall so that we can re-plaster the walls.