Susan: It has been colder than Block Island in a Nor-Easter today and I was out in it for the duration so that the only thing that still worked at the end of the day was my head, and I'm not too sure about that. Of course some would say that they are never sure about that, but Oh well. I've been thinking about your problem of lining a chimney since nothing else I needed to do this day required any thought. If you decide to line said chimney, here are a few considerations. The object is to keep the liner centered in the existing chimney and that is the purpose for the cement that you had proposed to use. Cement is not a good idea as it will bridge off and from the point of the bridge to the bottom the liner will be for ever hanging in space. They used to sell centering devices which look like hose clamps with little feeler wires all around. These are meant to keep the liner centered in the open space. One of these devices needs to be attached at the center of each section of pipe as it is lowered into the chimney opening. I think you can readily see that cement is not going to flow past all those little wires and that is why sand is the best option, but you need a fine sand that has been screened. Next problem is keeping the sand from flowing past the end of the installed pipe, which is not normally a problem as liners usually are installed from the top to the bottom of the a chimney, but in your case you only intend to line the upper portion, though in fact the whole thing is probably in equally deteriorated condition. If you put a metal skirt at the base of the liner that has been cut to provide a close but loose fit inside the Chimney and attach said skirt with a good clamp and several sheep metal screws, one at each tab you will have a base for the sand, but and there always seem to be one of those. Once the liner is in place and the sand has been slowly poured around it, the total weight of the sand will rest on the base plate which could cause the whole liner to begin a rapid decent toward the basement area, not a good situation. The Solution: Attach the afore mentioned skirt and the centering rings, also attach each section with three sheet metal screws or steel pop rivets at each joint. after the liner has been lowered to the desired level attach and screw a clamp that will hold the weight of the pipe against the top of the chimney. Now fill the space around the liner by slowly pouring dry Sack Crete around the liner. Be sure to pour slowly or it too will bridge at some point. You will probably have to mix your own mixture as most commercial products contain a gravel mix, or you could use pre mixed mortar mix which normally only contains sand. To guard against bridging use several long thin rods that can be slipped down along side the liner and moved up and down to keep the mix moving toward the base. Try to cover no more than 8 to 10 foot of the liner in a single days pour. Wait several days and start a second pour, but you might want to check with one of the rods first to see if the previous pour has started to set. The mortar or Portland mix will absorb enough moisture from the brick and the atmosphere to begin to harden after a few days. If it is very dry at the time you can put a little water down on top of the pour to insure a set. When the final pour is about one foot from the top mix up a watered batch and finish off around the liner at the top, troweling to form a slopped surface so that rain will run off. You will want to leave enough liner protruding from the top so that a suitable rain cap can be attached. Short of coming to Boston, which I have avowed never to do again, this bit of advice is the best I have to offer at this time. Good Luck and let us know how it all comes out. Dale in the Flat Lands