crumbling brick chimneys
And are the bricks literally crumbling, as in deteriorating, or are the faces of the bricks breaking off? If the latter, it would not be unlikely that the crown on top of the bricks is cracked or otherwise incapable of preventing water from getting inside of the bricks, which then freezes, and breaks the faces off of the bricks. So, you would want to make that an integral part of the project. If this is something that you wish to undertake yourself, post some pictures, as Tony suggested, and the fine people here will be able to provide direction.