Chimney Crown Repair

KellyJ · Sep 29, 2016

I have a stone chimney, and need to do some repairs, including to the crown, which has a few cracks. Removing it is a pain - I'm afraid I'll damage the stonework if I go at removing it. Is it necessary to remove it, or can I just pour an inch or so of new crown mix on top? It has a block liner, and there's enough of the liner protruding from the existing crown that adding an inch of thickness shouldn't hurt.

The existing crown, besides having cracks, also has no overhang, so I intend to build a form and add some overhang and a drip edge while I'm at it.

If I can't remove the existing crown would I be better off going with an elastomeric topcoat to seal it?

Thanks,

KJ

bholler · Sep 29, 2016

KellyJ said:
Is it necessary to remove it, or can I just pour an inch or so of new crown mix on top?

No you can pour on top of it but 1" is not thick enough.

KellyJ · Sep 29, 2016

Thanks!
Why isn't 1" thick enough? How thick would I need?
Is there any minimum amount of distance the flue needs to protrude from the crown?

bholler · Sep 29, 2016

KellyJ said:
Why isn't 1" thick enough? How thick would I need?

Well to start off what material are you planning on using? We use fiber reinforced concrete and the min we will pour is 2.5" but I vary the thickness depending on the size of the chimney to make the proportions look right. I have gone as thick as 6". But I would say 3 to 3.5 is the norm.

KellyJ said:
Is there any minimum amount of distance the flue needs to protrude from the crown?

I believe it is 2" but I am not sure on that.

webby3650 · Sep 29, 2016

I bet your old crown will come off easier than you think.

Often times the top flue tile is already either cracked, or a partial piece. Both most often!
Either can pretty easily be replaced with a taller section so you could pour a new crown over the old.

KellyJ · Sep 30, 2016

bholler said:
Well to start off what material are you planning on using? We use fiber reinforced concrete and the min we will pour is 2.5" but I vary the thickness depending on the size of the chimney to make the proportions look right. I have gone as thick as 6". But I would say 3 to 3.5 is the norm.

I believe it is 2" but I am not sure on that.

Well, I was going to use topping mix, which is intended specifically for applying a thin top (1/2" to 2") to an existing base.
But maybe I didn't explain my situation well: I already have a crown, so the proportions are already correct. I'm just asking if I can top that crown with a thin layer, to to ensure that the cracks in the existing crown are covered.

Thanks for your help!

KellyJ · Sep 30, 2016

webby3650 said:
I bet your old crown will come off easier than you think.

Maybe. I may give it another try, but I'd rather avoid the work. The problem is, it's on top of stones, and though in some areas it HAS separated, in others it is bonded pretty well to the underlying stone. Breaking loose the crown from the stone may also break the stone loose from the stack.

Thanks! And, you're right about the flue - I just realized I have extra tiles anyway, that I could stack on, to ensure the proper height above the crown.

bholler · Sep 30, 2016

KellyJ said:
But maybe I didn't explain my situation well: I already have a crown, so the proportions are already correct. I'm just asking if I can top that crown with a thin layer, to to ensure that the cracks in the existing crown are covered.

Yes you have a crown but no overhang right? If you are going to pour a slab with an overhang it needs to be more substantial if you want it to hold up. The proportions will be totally wrong and it will look strange if you have a 1" thick slab overhanging also. Most stone chimneys look much better with a thicker crown. And I have no idea about topping mix I have never used it.

KellyJ · Sep 30, 2016

Ah OK I'm with you now. 1" thick overhang would be too thin.

Thanks!

ccmac · Sep 30, 2016

I used an Elastomeric coating shortly after the mason finished my chimney and would you believe the crown was already cracked in a few places! They were very small and no real gap but still I was surprised. I coated the entire crown with 2 coats of "Duck Coat". I made sure to overlap onto the clay tile so as to cover the hairline cracks between the clay tile and concrete crown.

I also used "Chimney Saver" to seal the brick on the chimney as well as various areas of the house, such as window ledge bricks, ect...

webby3650 · Sep 30, 2016

ccmac said:
I used an Elastomeric coating shortly after the mason finished my chimney and would you believe the crown was already cracked in a few places! They were very small and no real gap but still I was surprised. I coated the entire crown with 2 coats of "Duck Coat". I made sure to overlap onto the clay tile so as to cover the hairline cracks between the clay tile and concrete crown.

I also used "Chimney Saver" to seal the brick on the chimney as well as various areas of the house, such as window ledge bricks, ect...

If the mason had done it properly then it wouldn't crack. There's a real process to doing it right, most don't take the time or even use the right materials...

begreen · Sep 30, 2016

Sounds like a great wiki entry or article. I will post if you folks can write it up.

ccmac · Sep 30, 2016

webby3650 said:
If the mason had done it properly then it wouldn't crack. There's a real process to doing it right, most don't take the time or even use the right materials...

Yep I have since learn that very same thing. Mine was not done correctly so I had to improve on it or I would have a lot of rain coming into the chimney.

webby3650 · Sep 30, 2016

I had to haul 1,000 lbs. of cement up a ladder a bucket at a time to fix mine. Would have been a lot easier during construction! It's all good now, no more crappy mortar soaking up water..

begreen · Sep 30, 2016

That's a lot of ladder trips!

bholler · Oct 1, 2016

begreen said:
That's a lot of ladder trips!

Yeah we do it all the time It sucks. But we usually try to at least use a rope to pull the buckets up.

Fivehorizons88 · Oct 6, 2016

bholler said:
Yeah we do it all the time It sucks. But we usually try to at least use a rope to pull the buckets up.

What type of product do you recommend for crown repairs? Mortar, cement, etc...?

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