Fireplace/ chimney grouting

[DRP]

I was having a discussion with our mason today over grouting the block surrounding a residential exterior fireplace and chimney. The block will be faced with 6-8" of stone on the exposed faces. The back of the fireplace is over 1" from a wood framed wall sheathed in 1/2" osb, tyvek, and then covered in hardi board panels behind the chimney. The block is 8", the firebrick are laying down flat, so the min thickness of the firebox is 12".We are in seismic C. Does the block need to be grouted solid? If so, how high does it need to be grouted?

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[ICE]

Is there a set of plans? How about re-bar? I would think, why not grout it? Is the mason worried about it getting too heavy for the foundation? Obviously, I don't know much about fireplaces. Actually, I can say that it's more like nothing about fireplaces. So don't pay any attention to this.

 

[rogerpa]

We are in seismic C. Does the block need to be grouted solid? If so, how high does it need to be grouted?

2009 IRC

R1001.5 Firebox walls. Masonry fireboxes shall be constructed of solid masonry units, hollow masonry units grouted solid, stone or concrete. When a lining of firebrick at least 2 inches (51 mm) thick or other approved lining is provided, the minimum thickness of back and side walls shall each be 8 inches (203 mm) of solid masonry, including the lining. The width of joints between firebricks shall not be greater than 1/4 inch (6 mm). When no lining is provided, the total minimum thickness of back and side walls shall be 10 inches (254 mm) of solid masonry. Firebrick shall conform to ASTM C 27 or C 1261 and shall be laid with medium duty refractory mortar conforming to ASTM C 199.

R1003.10 Wall thickness. Masonry chimney walls shall be constructed of solid masonry units or hollow masonry units grouted solid with not less than a 4-inch (102 mm) nominal thickness.

In the D group SDC's the "grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion."

I think that this is a "best practice" for any masonry chimney.

1996 BOCA

2115.3.2 Space between liner and chimney:

Liners shall be separate from the chimney wall, and the space between the liner and masonry shall not be filled. Only enough mortar shall be placed to make the joint and hold the liners in position.

 

[DRP]

Thanks for the reply Roger, I had been back as far as my 2000 IRC last night, minor changes but nothing got us off the hook. I'll admit this is not a chapter I had done anything more than flip though to check flue sizes in the past. I saw R1001.5 while checking the flue dimensions and we then sat down for a read. I offered and was asked to check with you all for any exceptions I might be missing.

I ordered 7 tons of pea gravel yesterday afternoon and it arrived first thing this morning. This wasn't met with great enthusiasm so I helped mix and pour, cleaned gravel out of the toys after and stuffed rebar in the cores. We'll pour every 6 feet or so, this will leave cold joints but assure that we get it down. There is a space between firebox and block and the basement flue and block so we should be good there. I have seen the results of tight packed flues and lintels. No reinforcement is required but we had already discussed 6 sticks, 3 per side in between the blockwork and the thick stonework as well as 2 bond beams as he goes up. He really does nice stonework and is a good mason with many fireplaces under his belt. This was simply something neither of us has ever seen in local work. The question of the day is why? Are we trying to provide strength, block the passage of gasses, or?