DIY Chimney Crown

[david_]

Decided to tackle this prior to cold weather this year. Recently cleaned the chimney and hated the busted up crown. No good companies I can find close, so decided to do it myself.

Starting point:


Removed mortar and top layer of brick to allow for a thicker crown and flue tile exposure:


Day 1 Progress:


Adding some mortar to reinforce my new top layer and to better support crown support structure:


My plan is to use floating angle iron / cement board to create the base for the crown. I'll use 2x6's around the 2x4's for the form and leave a couple inches of flue tile exposed on top. I will provide room for expansion around the tile.

I might use a line of caulk on the 2x4's for my drip edge, or just come back after with a grinder and notch under the 1.5" overhang.

 

[Garbanzo62]

Check with Begreen and/or Bholler, I think you need some sort of expansion joint between the cap and the terracotta

 

[Prometeo]

I would probably apply a sheet of welded mesh, removing the excess and the central part of the flue, obviously, and make a good base in concrete, not premixed, and wetting the bricks first, but without excess water. The slope must be towards the outside, and if possible, a profile to let water drip without touching the bricks. The thickness of the concrete should be at least 3 inches

 

[bholler]

Yes you need an expansion joint around the clay. And a bond break between the chimney and crown. Don't use metal reenforment use fiber in your mix.

 

[david_]

Yes you need an expansion joint around the clay. And a bond break between the chimney and crown. Don't use metal reenforment use fiber in your mix.

Does my plan to create a sheet metal/hardie board base for the entire crown qualify as a "bond break"? Or is there an easier way, like just put a layer of tape/cardboard between the chimney bricks and the concrete crown?

I imagine the crown will not fit perfectly flush against the brick if it's poured on top of a hardie board base, and will just be resting on my mortar bed in the last photo. Should I caulk around any gaps there?

 

[begreen]

 

[bholler]

Does my plan to create a sheet metal/hardie board base for the entire crown qualify as a "bond break"? Or is there an easier way, like just put a layer of tape/cardboard between the chimney bricks and the concrete crown?

I imagine the crown will not fit perfectly flush against the brick if it's poured on top of a hardie board base, and will just be resting on my mortar bed in the last photo. Should I caulk around any gaps there?

Put a sheet of plastic under or over the cement board

 

[david_]

Thanks all!

Had to re-set this top tile with refractory mortar. Built the form up and fit my cement board.


Will add a piece of plastic below cement board prior to pouring, and the flue expansion joint.

 

[Prometeo]

I don't understand those iron bars and that panel, under those iron profiles there is no empty space, the concrete does not pass through very narrow spaces, instead of that panel put electrowelded mesh, it will keep your work intact over time.

 

[begreen]

I like bholler's suggestion of using fiber in the cement instead of metal. That adds a lot of dimensional stability without concerns of longterm corrosion.

 

[Prometeo]

I have used fibers several times, and well-known products, prestigious brands, the results are not comparable to classic iron and concrete, all those mortars will end up creating cracks, it's like saying that the iron of a reinforced concrete beam can be replaced by fibers.
Concrete protects the irons if the job is well done

 

[begreen]

Our whole garage floor is done with fiber reinforcement. No cracking after 12 yrs.

 

[david_]

I'll check out the mesh instead of the board. Lower profile might fit my chimney better. And I don't mind adding iron reinforcement in the fiber reinforced crack resistant concrete I bought.

 

[Prometeo]

@begreen
garage concrete here is done without mesh and without fibers and there are no cracks. If instead you have to make a concrete slab outside, accessible by car, and directly on the ground, the mesh definitely holds up better than fibers. Fibers have their uses, certainly. But if I have to build a hat that keeps the bricks in one piece, I believe in electrowelded mesh then if I want to add fiber it's something more.

 

[bholler]

I have used fibers several times, and well-known products, prestigious brands, the results are not comparable to classic iron and concrete, all those mortars will end up creating cracks, it's like saying that the iron of a reinforced concrete beam can be replaced by fibers.
Concrete protects the irons if the job is well done

No iron in structural beams can't be replaced with fiber. But a crown isn't structural it simply needs to resist cracking. Which honestly with a bond break and expansion joint it really doesn't even need fiber. But I have seen way to many crowns or concrete in general fail when the steel corrodes.

 

[Prometeo]

@bholler
I'm perfectly agree, but simply from my experience I believe that the electrowelded mesh maintains the single piece, only with fibers, I'm not sure, between sun, frost, it remains all one piece, concrete degrades if it is not well made.

 

[bholler]

@bholler
I'm perfectly agree, but simply from my experience I believe that the electrowelded mesh maintains the single piece, only with fibers, I'm not sure, between sun, frost, it remains all one piece, concrete degrades if it is not well made.

Fiber is the recommendation of the brick institute of America. And we have crowns out there done that way that are now pushing 30 years old and are still in great shape.

And yes of course the mix needs to be right. If not it will erode or degrade quickly.

 

[Prometeo]

@bholler
the mix must be right, but also keep an eye on the weather, (too hot or freezing is not good) the seasoning, wet the concrete often in the first few days, and the thickness, 1-2 inch concrete would be poor.

 

[david_]

Okay.. finally ready for pour in a couple days when the weather is good. I bailed on the concrete board and I'm going with two layers of the mesh for the base. I have the rebar there in case I want to use it. And a cut-up trash bag which will be trimmed to size for my bond break. I also sealed the form seams with silicon.

 

[Prometeo]

make sure the mesh has an inch and a half, at least, Over and under of concrete, and also all around, While the metal mesh with tight mesh leave it underneath, completely, or remove it, no need here, in that video it was used inappropriately like a support, but you already have.

 

[david_]

Pour went well I think. Used about 250lbs of fiber reinforced crack-resistant concrete.

I'll let it set a few days and carve out a drip edge underneath with a concrete cutting wheel.

 

[Prometeo]

keep it moist for a few days, looks like a nice job, congratulations

 

[david_]

Removed form and foam, sealed around tile, and cut in a drip edge on underside. I think I'm done here.

 

[Prometeo]

very nice, you could try the drip system if it works, either way you will be ok for the next 50 years. Happy New Year !

 

[thewoodlands]

Removed form and foam, sealed around tile, and cut in a drip edge on underside. I think I'm done here.

View attachment 321839

Nice job, have you thought about water proofing it?