Topic :Chimney Stains
What causes white chalky discoloration on the exterior of a chimney? What can be done about it?
Most likely the white chalky stuff is caused by minerals working their way out of the mortar. I would recommend a sealer designed to seal concrete. There are a few good ones out there…I think Flood (name brand) makes the best. You should apply it every 2 years for best results. As for getting the staining off, try vinegar and a scrub brush.