Fireplaces, Heating Stoves, Flues and Chimneys - Chimney Masonry Repair

I have two separate chimneys for furnace and fireplace. The oustide concrete for furnace chimney is cracking and some have already fallen off. We recently installed a new stainless steel liner which was probably the cause of the cracking. Another reason is that the previous owner decided to go the cheap route and not wire the chimney before applying the concrete. Since part of the chimney has already fallen off, what is the preferred method to fix this and to prevent future cracking and breaking off?

I'm concerned my fireplace chimney may crack and fall off in a few years similar to my furnace chimney so I thought of possibly applying some waterproof to prevent the cracking.

Any recommended products? Is this Chimney Saver product any good?

Since the previous owner stucco both chimneys without any wiring, do I have to have the knock off all the stucco and start from scratch? Is there another solution?

If water already penetrated and you hear a hollow sound when knocking on it, will waterproofing the stucco fix the problem?

Please help!!! I really need some advice. Thank you!

You may want to post in the masonry forum: Bricks, Masonry, Asphalt and Concrete - DoItYourself.com Community Forums (http://forum.doityourself.com/bricks-masonry-asphalt-concrete-3/)

is the chimney under the stucco block or brick

The furnace chimney is block.

I dont know about the fireplace since the cracks are not so bad that the stucco is falling off.