Chimney cap to flue gap seal

Hi,
Had some chimney work done today. After reading some chimney construction wisdom, I asked the guy to leave a small gap, about 1/4" between the cap and the flue (terra cotta). This gap is to be filled with some flexible sealant. We made the gap with a piece of cardboard, which will be removed after the cap mortar sets.
Recently someone mentioned DEFY Chimney crown repair, which would work I'm sure, but it costs a bundle and I do not need nearly that much.
Can anyone recommend what I could use for this purpose?
Regards,
RichK
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They sell a high-temp silicone caulk. I've seen it at Lowes and H.D.
Bob
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Thanks Bob,
Been to both and have not had any luck finding it. Can't even find it on the net. Help Line from DAP suggested using their Polyurethane caulk, but it does not spec temp anywhere. Guy said it's good up 200F, but I'm not so sure.
Regards,
RichK

I'm
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RichK wrote:

Virtually any RTV silicone is good to well over 200F.
I don't think there's any chance at all the temperatures at that point will be a problem for any high quality silicone caulk.
How deep is this crack and is there anything backing it to help fill the void?
--
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It's not a crack, but a 1/4" (or so) gap, the depth of the crown, left by the mason, between the flue and the crown. When the cap mortar sets, I want to fill that space with some flexible sealant.
Some people recommend using this method to prevent crown from cracking. Sounds good, but now I'm having problems finding something easily available to use for that purpose. DEFY product is expensive and sold 1gal quantities.
Regards,
RichK
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RichK wrote:

Fire rated from DAP...note even here its service rating is 160F http://www.dap.com/docs/tech/00077364.pdf
DAP Premium Roof and Flashing Sealant http://www.dap.com/docs/tech/00077348R.pdf Physical & Chemical Characteristics: Volatile: Xylene Solids: 90% minimum Service Temperature Range: -40F to +185F
Note it's rated higher actual temperature than the fire-rated product.
"High temperature" is only used/needed around the actual outlet of a stove or similar heating source into the exhaust duct or chimney and will typically be rated at something like 2000F, not 200F.
I've used just ordinary "off-the-shelf" clear adhesive caulk/sealant for making probes into large diameter pulverized coal feed pipes in power plants operating w/ air temperatures of roughly 190-200F and had no problems with them withstanding the positive pressure and temperatures for weeks.
There's no way the temperatures at the outside of a chimney flue at roof level are going to approach 200F during weather during which a fire/furnace will be operating.
I think you're into the way over-specification region here for an unwarranted concern.
As for the "crack", I understand the gap, I was trying to find out what was behind the gap to judge the difficulty of filling the gap. If it's more than 1/4" deep or has no backing I would get some of the gap-filler material for backing caulking an insert it first.
HTH...
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wrote in message

Yep, last one I did I left 1/4". 5 gal paint sticks from the Borg perfect size. Also good when 1/4" gap required between flooring and wall.

Yep, but more important to keep the flue from cracking because of the cap. That was my belief.

Just a professional wanna-be here but I've always used polyurethane - Henry (900?) or one of the PL's. Good stuff while you're up there to cover/re-cover any exposed roofing nail heads. Doesn't dry out over time exposed to sunlight like roofing cement.

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Thanks Bundy :-)

Is the gap in the floor to prevent squeaking? Please tell.

I read about the gap on askbuilder.com. Idea is good, but seems the article was written purely to advertise DEFY product, which is expensive and easily available. They answered my e-mail, but failed to recommend anything, which is pretty self serving.

Yes, picked up a tube of PL Polyurethane Roof & Flashing Sealant. HelpLine guy from DAP suggested his own polyurethane, but I could not find it locally.
http://www.dap.com/product_details.aspx?product_id 
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Wood product floors. Expansion and contraction to prevent bowing, humps, buckling, etc. Different gaps for different products.

We're all just capitalistic pigs when you come down to it.

Al... <Today the painters tool was lonely. No activity. Roofing nailer happy though>
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At lowes, IIRC, it was located near the high-temp stove paint.
Bob

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