Veneer Mortar for the Chimney

Hi -

Should I be using a high temperature mortar when I veneer the chimney? Also when I mortar over the chimney pipe flange should I have a slight slope away from the chimney pipe?

Thanks very much.

Your chimney gets hot and occasionally takes direct heat when flames happen to go up (which should not be very often and you shouldn’t make a practice of that!). I’m not sure though if you’re asking about mortar between the veneer pieces, or mortar to adhere them to the chimney. @BrickWood has more experience with that and I’ll raise the flag for him to help you there.

For sure. You are making what’s called a chimney crown, and it must slope away from the pipe or else water will pool there. In cold climates that will cause cracks as ice breaks apart your mortar, and in all climates will lead to water dripping down onto your hearth, carrying some dissolved creosote with it.

I guess both. Isn’t the same mortar used for making the veneer adhere to the firebrick and to fill in the joints between each veneer piece?

It depends, which is why I would like @BrickWood to weigh in on this. He knows these things inside and out, and especially the right questions to ask. Thanks for your patience on this, Greg. You won’t be at that step for a little while, and the answer won’t stop your progress on other tasks.

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Hello Hello!

Yes, that chimney area gets CrAzY HOT! So you absolutely, positively, unequivocally have to use high-temperature mortar on the fire brick for the chimney. Now… if you are applying a veneer onto the chimney, you absolutely, positively, unequivocally have to wrap the firebrick chimney with ceramic fiber blanket & stucco before applying your veneer.

Chimneys can get hair-line cracks - and if you adhere your veneer directly to your fire brick, your veneer will also crack. That’s a given.

Secondly - your DuraTech Chimney Cap (that we recommend) will cover the anchor plate so the edges of your anchor plate are covered. But if you want to take the extra step of applying some mortar on top of the anchor place (and sloping the mortar so the rainwater runs off) you can… but remember - mortar does NOT adhere to metal and with that intense heat, it will eventually flake / fall off.

And before you ask “are you sure it will do that”…

Yes. I’m quite sure. Been There. Done That.

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Hi @BrickWood

Thanks for responding to this thread. Yes, I have used high temperature mortar for all firebrick including the chimney.

My mortar / veneer and chimney cap questions about the chimney stem from the instructions. Step G of the the instructions state: “Apply the veneer onto the chimney. If possible apply veneer OVER the bottom of the anchor plate.”

If I wrap the chimney with ceramic fiber blanket and stucco/ mortar then the front of the chimney will no longer be flush with the front of the oven, the front will extend 3" over the front of the oven. Maybe I’ll just leave the firebrick on the chimney exposed.

Thanks very much.

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Well, that also depends, Greg. Are you also applying veneer to the front of the oven? Or closing off the front, as many do?

If you do that, you will have your 3 inch extension to the front, a protected chimney as @BrickWood strongly recommends, and an oven that retains more heat.

The instructions for closing off the mouth are purposefully a little vague, as they are more guidelines for design than a rigid blueprint, but it is a relatively easy task.

May I suggest: place a crown on the chimney first, with sloping edges. Place the DuraTech cap on top of it, with the included high-temp silicone seal as instructed. Use a damp rag to smooth the silicone so water won’t get dammed up on the anchor plate, and be careful not to pull silicone out of the opening between anchor plate and chimney crown.

The silicone does two things: it keeps water out of the chimney, and it keeps smoke and flame from escaping under the anchor plate so all that heated air and smoke draw properly through the chimney cap as designed.

I think you can safely omit placing veneer on the chimney top. It can be a nice touch, but it doesn’t add that much to the look—and veneer is 100% for looks. (In my opinion, anyway.)

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I was originally planning to partially enclose the mouth of the oven with brick. I’ve since decided to have a metal lip / flange made to partially enclose the front, it’s going to be 1/8 inch thick stainless steel.

Sorry, I didn’t mean to raise a bunch of questions. I was just trying to reconcile the instructions for putting veneer on the chimney.

No worries, Greg. Our conversation can help other people, too!