Fireplaces, Heating Stoves, Flues and Chimneys - Laying Chimney Block

I am about to have my old chimney torn down (about 33 blocks high) and a new Cement block chimney built. This work will be done by a local contractor.

I have been told that you can only lay so many chimney blocks a day to allow the mortar to harden before adding more weight.

Can you tell me how many blocks should be layed at one time and how long before the next set of blocks should be layed? I would also appreciate any other helpful advice on things to watch out for.

Thanks in advance
Ron

There is no need to slowly lay the chimney block. The critical item is to make sure the chimney is sufficiently braced or set up enough to progress. Actually, the weight provides compression of the mortar, which is what you do when you tool the joints.

Make sure that you lay the chiney block in unison with the flues. You will use 3 block for each flue length. Use refractory mortar for the flues.

Dick

Thanks Dick, I appreciate the information. As for the proper bracing and refractory mortar, I will consult the contractor on how he plans to do this.

I'm not real knowledgeable about this work (I'm a certified welder) but I guess common sense will guide me the rest of the way.

Thanks again for the info.

Ron

Be sure you and the contractor are clear on the use of refractory mortar. It is a lot more expensive than regular mortar and it's apparently common practice to just use regular mortar throughout. When I built my chimney, even the guy at the place I bought the block said that's what local contractors do.

The use of refractory mortar is well advised but it is not necessary to use too much of the stuff. I used to keep my bucket of refractory right on the scaffold as I laid up the heavy blocks and I reached in and got a small amount on the back of a pointing trowel and applied just enough to spread and seal the tiles together.

One of the most important elements of your chimney will be the cap. Spreading a bed of mortar sloped from the tile and sloping off the top is not by any means an acceptable method. The best thing to do is to obtain a pre cast cap of reinforced from the dealer you got the blocks from. This cap gets mudded to the last course pitching off from next to tile liner to edge of block and it extends at least an inch over the edge of the chimney block. This method will hold up well and protect water and frost from getting into the top block and damaging the lightweight block due to frost and moisture.

One more tip, those clay liners are not always cast out precisely square and sized exact. Try to keep the tile liners plumb and centered in the cavity within the chimney block. To keep them centered and spaced, try using wads of raw spun fiiberglass insualtion stuffed between the block and the liner where needed to try and keep the liner spaced and unhampered Block or brick masonry chimneys with clay fired liners should never be used to vent gas fired appliances without installing a flexible stainless lining.

bs5

md2lgyk & bs5,

Thanks for the additional tips. I hate to tell a contractor how to do his job when I don't know what I'm talking about, but I will discuss your suggestions with him and hope for the best.

Sorry for the delay in responding. Wish I would have checked the "Notify me when new posts are added". :(

Thanks again
Ron

Technically, you only need refactory mortar where there is direct contact with flame. Above the damper, regular mortar is fine.

Not so. IRC R1001.9 says nothing about "contact with flame."

It doesn't. What it says is (R1001.8) "Firebrick shall conform to ASTM C 27 or C 1261 and shall be laid with refractory mortar conforming to ASTM C 199."

So, if you are using firebrick to line the throat, smoke chamber and chimney stack you should use refactory cement. If not, then you don't need refactory cement (and you don't need to use firebrick above the firebox).