Bricks, Masonry, Asphalt and Concrete - Fixing crumbling brick/mortar?

During a bedroom remodeling project, i exposed a section of my chimney in the bedroom closet. There are a few bricks and some mortar that is crumbling. I dont' think its enough to worry about the strength of the chimney, yet. I had a chimney guy look at it and he told me that there is a cement/plaster type thing to put over it just to kind of seal it up and keep it from getting worse. Anyone have any idea what i can use, or what he's talking about? Thanks
-Ryan

can you post pictures on an external web site - like photobucket - and post the link here? also, how old is this chimney?

the proper way to fix crumbling mortar is to grind out the joints and repoint them with new mortar. the bricks have cracked because the mortar between them crumbled. once new mortar is in place, the bricks should be fine. but plastering over the problem won't fix it - it'll only hide it.

you - or a mason - should do a little at a time, depending on the extent of the decay, to avoid compromising the structural integrity of the stack.

also, look at the roof where this chimney penetrates and make sure all of the mortar, flashing, bricks, and the cap are in good shape. after all, the bricks and mortar are all the same age from the ground up.