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

My house, built in 1960, has a very large chimney with four flues. I'm not sure of its correct name (have heard it called the crown and also the wash), but the sloped part at the top of the chimney is cracked and deteriorated. It seems a fairly straightforward job to remove what's there and replace it, but I'm not sure what material to use. Is there some special type of mortar for this application? Or perhaps concrete? Do I need reinforcing mesh or rebar? Any particular tricks to a repair like this? I've worked with concrete and mortar before so am familiar with the general techniques involved.

You want to use a very rich mix to cap it off. its a lot in how far do you want to go here. lots of times on a big chimney we put a big thick cap on it with a drip edge and be done with it. The drip edge would stick off the flue there about 2"and be about 2" thick at the edge there and slope up to the tile. build the form out of 2x4. you can put some 6x6mesh in it to help hold it. Take all the old cap stuff off


ED ;)

Thanks for the reply. What you describe is exactly what I've thought of doing. I did get an estimate ($1000) from a chimney place who said they recommended using concrete instead of mortar. They also said that to meet code the cap would have to hang over the edges of the chimney 2 inches or so. That part I don't like - the chimney is block faced with stone, and I just don't think an overhang would look right.

Exactly how do I achieve a "very rich mix?" All I've ever done in the past is mix mortar as it comes in the bag. I presume I need to add more of something to it?

You for sure want to use a concrete mix up there. A rich mix is just add some more cement to this mix for on top of the chimney. What that over hang does there is get the water off it so it cant like run down the side of the chiminey. Water will work its way down a chiminey and inside the home by what they call hydrostatic pressure. You do want the under side of the drip edge to angle down and out a little.

ED ;)

Thanks. Sounds more and more like something I can do myself. I do understand the purpose of the overhang but still don't think it'll look right.

I have a similar problem. The chimney is for a fireplace insert. I am concerned about how much the chimney top may weight. How thin can the concrete be when replacing? The top is appoximately 7' by 4' and a concrete slab that size can weigh alot if the concrete is thicker than 2".

Thanks for any inputs.

you could try and use soapstone or slate, but their weight may not allow for them to be carried to your roof height. otherwise the above answers are the way to go.
I just repaired a crown where the mason of 15 years ago decided that the leftovers go on top (14 inches worth)!