Seal flue and thimble

I would use Rapid Set Mortar Mix as recommended by Steam Doctor in this thread:

https://forum.heatinghelp.com/discussion/192052/sealing-4-gas-wh-vent-to-masonry

It's good general purpose stuff, cheap, and then you have 50 pounds left over for masonry repairs.

If you already have structolite, this is the perfect place to use it. Remove that old piece of metal pipe (unless it is the end of a liner, then just clean it up. Then place a new piece of single wall vent pipe in that opening. after the vent is connected to the appliance (HEATER) apply enough structolite to seal the operningbetween the pipe and the crock.

I do not recommend Great Stuff Foam. I'm not sure what temperature that STUFF is rated for. (Get it STUFF HAHA).

seized123 said:

Thanks @jesmed1, I just looked up Rapid Set and they said not for high-heat applications over 300 degrees, and I know the air in my flue can reach 500 degrees. The submittal for Structolite has no such warning and says: “Gypsum plasters specially made for fire-protection applications and used with specified plaster bases, provide excellent fire protection,” so I’m leaning that way.

Then there’s furnace cement which I assume from the name alone is fine for high heat. I think @EdTheHeaterMan likes the characteristics of Structolite better, though I don’t know if he’s used it where the potentially very hot glue pipe goes into the thimble. If I’m lucky he’ll weigh in here.

Been using for years. I have gone back to jobs, years later, and looks good as new. Just curious, where did you see temp ratings? Thanks. 

I am not good with pictures (more of a blood and flesh guy) but you might be better off removing the thimble. You don't want to rely on the thimble to carry the weight of whatever sealant you are using. If the Gap in the chimney is too big, stick some bricks inside and seal around.

Regular mortar was commonly used between the pipe and the thimble in the past and it is fine and will last a long time. Never mind the temp rating. Many chimneys were built without a clay liner and lasted 100 years or more with the bricks being held together by mortar.

If your concerned about the temperature rating, you could also use high temp silicone. Home Depot sells it . Look in the stove & fireplace dept. They don't have it in the paint dept with the caulking where it belongs.

realliveplumber said:

I use and would recommend mortar to seal the thimble.

Mortar is what the entire chimney is made of.

I would suggest not to use Structolite, which is gypsum based plaster, in this litigious society.

If something tragic were to happen, and you were on the witness stand, and counsel asks you, "why did you use gypsum plaster to seal the connection?" What will your answer be?

If they ask you "why did you use mortar?" You can answer "because thats what is holding the entire chimney together".

Our continuing education instructor drills it into our heads every class. Its not if you will be sued, its when.

If something tragic were to happen, and you were on the witness stand, and counsel asks you, "why did you use gypsum plaster to seal the connection?" What will MY answer be?

Members of the jury, Your Honor, and to you Mr. prosecutor, I have used this product for years as a professional oil burner technician, It is fire rated as a non combustible when applied to metal lath on wall from as far back as 1906. Many homes of that time were built with wood lath to hold the gypsum based plaster on ceilings and walls and had a fire rating of more than 1 hour, When applied to masonry or metal that fire rating is much longer.

I was first introduced to this product from a professional chimney repair man in 1972. The chimney professionals have used this as a removable fire-stop material for flue pipe connectors on chimneys since it is easily removed and replaced when a vent pipe connector needs inspection and maintenance. It was created many years ago and was first discovered to be used in Egypt on a pyramid that was built in 3700 BC. That pyramid has not burned down in all those years and I see no reason that this product was the cause of the occurrence that we are here discussing today. Besides, the crane that caused the chimney collapse had no effect on the vent connection. The death of the canary in this case was a result of carbon monoxide poisoning from the gaping hole in the 5th floor bedroom where the chimney collapsed. The basement connection and sealer were actually still intact when the fire marshal completed his initial inspection as shown in these photographs marked exhibits 37 through 59.

If you really need to know @realliveplumber .

And then the crane operator will make a spontaneous confession that he was asleep at the controls at the time of the accident, as Perry Mason asks for a complete dismissal of all charges to the structolite installer.

This is why I mentioned @Bob Harper. No need to worry about anyone quoting different codes, as he is the code. He knows them, he influences them, he sits on boards that writes them.

LOL. My fan club. Thx Steve. I apologize but I've been planting my mother in law today.
NFPA 211 calls for connectors to be "firmly cemented to masonry." Here, cemented is a verb. It means to adhere, connect, make firm, unite, or attach.
Mortars are typically made with lime (up to around 1930's) then ordinary Portland cement (OPC). This coincides with the widespread use of terra cotta clay flue tile, too. In the Philly area, many old homes were relined with tile by lowering tiles with the bottom edge buttered with OPC-mortar. These were rarely stacked properly nor were the joints struck properly. We see these failures on video inspection. The OPC mortar falls out, erodes or decomposes. When flue gases hit the alkaline mortar it forms soluble salts and sand, which is often seen as sand in the base of the flue such as the cleanout door pictured.
As for forensic investigations of mortars allow me this please: The Standard calls for it to adhere or 'cement' the steel pipe to the masonry (think glue). If it allows movement of the pipe, it is ineffective or has failed and needs to be replaced. If there is an "Oops!" that results in an investigation into why a connector slipped out of a thimble then yes, a sample would be tested and analyzed. Even if it was a viable cement when installed, if everyone ignored it for years as it broke down instead of replacing it then liability would attach. If the failed mortar is found to be the proximate cause of the incident, then yes, you'd better worry.
As for std. masonry mortars used in chimneys, they are allowed to lay the outer wythe walls but not flue tiles. The codes have called for refractory cement in flues since 1927. A chimney pro can spot non-refractory mortars on video inspection. Also, the joints should not exceed 1/8" and be struck smooth.
Note that since a steel connector must extend to the inner face of the flue, there must be a seal where it penetrates the thimble. Therefore, it must be attached or secured and it must seal. Many masonry materials can fill gaps or seal when new but later degrade and fail. Thimbles that attach to the inner face of a flue tile must meet the same requirements as flue tiles- be tested and approved to ASTM C 315 and be set with a medium duty non-water-soluble calcium aluminate refractory cement mixture. Most people refer to this as '211 mortar'. It is a dry powder you mix in small batches for just that joint, discard any remainder then repeat at the next joint. Regular refractory mortars, such as common furnace cement must be tested to ASTM C199.

Keep in mind, the entire connector must be accessible for inspection, service or replacement. If you entomb a connector into a masonry wall it should be stainless steel. The std. calls for galvanized steel pipe if a minimum gage thickness. This, however, cannot be met where galvy connector is left in masonry being eaten daily by acidic flue gases, water and soluble salts. As soon as the zinc coating fails or the pipe rusts, it must be replaced.
In order to be able to meet all the requirements, connectors buried into walls should be ss without joints. That means use rigid ss chimney liner stock. Regardless, all connectors must slope up to the flue 1/4" per LF. That includes the section buried into the wall. Most are level, which is wrong. On masonry flues, there must be a cleanout 12" below the breeching as shown in the pic. Listed liners, venting and chimneys do NOT require cleanouts.
HTH, Bob

Planting? A term of the utmost affection, I'm sure. You did say Mother IN LAW.

My condolences also.

I have a query for @Bob Harper

I am no longer servicing oil burners since my retirement. However I did use Structolite, which is used primarily as a base coat for plaster walls, to seal the connector pipe to the chimney base.. There was this old-time chimney installer/repair company in the Greater Philadelphia area that used it for sealing connector pipes to chimney crock or chimney bases. I learned about this stuff from them.

You could mix it to a consistency that would stick to the pipe and the crock, or even to chimney bases that were holes where bricks were left out. That stuff would stick and hold, seal openings as much as 2” gaps and stay in place. Also it did not shrink as does the premix furnace cement. When I returned next year to do the maintenance. It looked as good as the day I put it there last year.

Was that a non-approved sealer for connector pipes?

Just asking for a friend.

Was on a job recently. Seasonal boiler maintenance. Flue pipe was stuffed into hole in masonry chimney. Gap was sealed with aluminum foil (as in the stuff you use in the kitchen). Can't make this stuff up.