Chimney Cap/Crown mortar that will not crack?

Hi All,
Had a guy repair the top of my chimney including a new cap. A week later I get on a roof and the cap/crown is already cracked. Had the guy leave a gap between the crown and the flues (2), so I can fill it with flexible sealant, but that apparently did not help. I live in the Midwest.
Can anyone point me to a mortar formula for a mortar that will crack in such a short time? Guy says he used the following:
1 part acrylic to 3 parts water 2 parts sand to 1 part Portland cement
Apparently this is not a good combo.
Regards,
RichK
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Who cares what formula he used. Get him to replace it. You wanted a new cap not new cracks. Or was his warranty good only as long as you could see his tail lights...
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Silicone mortar caulk has lasted longer than any cap I have replaced. After the third on in 10 years I turned to the caulk which has been there for 5 years with no signs of separation.
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Well...at this point I'm not sure if I want someone to hammer on the chimney to crush the new cap. I sealed it for now with a roof sealer - the kind that's applied with a trowel.
At this pace I will be looking at a new cap in year, I suspect, so would like to prepare by learning what mortar works. OTOH - who knows after the one crack relieves the tension, it may last for a while.
RichK

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Hello,
I did my own chimney crown using a ready-made sand/cement concrete mix that I bought at a local diy store here in montreal. I used a small full length of rebar (for an approx. 20 inches square chimney) to ensure no cracking would occur. I poured the crown in my garage for a better control over curing (~ 7 days, wetting every day). It's been 2 years now and the crown looks like new.
Make sure you do not use a brick mortar mix to create the cap. More often then not, masons use the same mix as they used for bricklaying to pour the crown and this results in cracking.
There is also the option of buying a pre-cast crown (if you have a standard chimney size) for around 50 $ My next door neighboor chose this option 6 years ago and it is holding in place, no crack.
Christian
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RichK wrote:

layers of Rustoleum exterior epoxy concrete paint .. .. ..
http://www.saversystems.com/trowelable.php
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Thanks Bob,
This stuff was mentioned here before, but it's expensive as hell and practically "mail-order" only.
Find it strange that no one has revealed a working chimney cap mortar mix. It's either obvious, or secret. Not so obvious to me, as in two cases (mine and friends) the cap cracked soon after being re-done. Two unrelated "masons" did it. Have browsed the web and nothing comes up, as far as mortar, just folks trying to sell you goop.
Have another friend who wants his re-done, but after these two cases, he's waiting until he's comfortable with a mix that might hold up a year or two :-(
RichK

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