Seal flue and thimble

seized123

What would you use to seal gap between the galvanized pipe and the .. is that a thimble? (See photo.)

I know @EdTheHeaterMan has recommended Structolite at least for where the thimble hits the wall, I wonder if that would be good here too. Great Stuff Fireblock would be by far the easiest, but I don’t know if it’s appropriate here.

jesmed1

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.

seized123

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.

EdTheHeaterMan

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).

EdTheHeaterMan

Not a fan of Furnace cement. it warps and separates from the surfaces because it shrinks as it cures. leaving very sharp edges and a poor looking finish. A professional product that makes your work look far from professional the next day.

STEAM DOCTOR

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. 

seized123

@STEAM DOCTOR here’s where I saw it, in the “Application” section:

STEAM DOCTOR

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.

EdTheHeaterMan

Does this mean that mortar mix is dangerous when applied to my fireplace and chimney bricks. I know some really old masons that have been putting mortar between bricks on chimneys for years. I think the stuff between the bricks on my fireplace and chimney is mortar. Should I have it tested for fire safety? Who would know if it is safe? The fire marshal? The chimney sweep? Maybe the salesman at Home Depot?

What if the Lowes associate disagrees with the Home Depot associate? Will I ever be able to use my fireplace again? And will Santa be safe entering my home this Christmas Eve? What is a person supposed to do?

I'm sticking with Structolite. Problem solved!

seized123

I was all set to get Structolite but I’d have to buy a 50 lb bag and what would I do with the 49.625 pounds I’d have left, so I just bought a container of furnace cement that everyone uses. It did go on really easy, it might curl up like you said but if I had all that Structolite left over I’d end up plastering my car, flowers, dog, driveway, mailbox, and I don’t have time for all that.

EdTheHeaterMan

I try to get plastered at least once a week. perhaps a 10 year old single malt.
Since you have the premix tub of furnace cement, then you can go back the next day and touch up the gaps in your work, then check it in a week, you may need to touch up again. The smeller the void you fill the less the shrink factor will matter.

Just be careful when removing it next year for inspecting the chimney base. That stuff hardens like steel and where it peals off, the edge sometimes can be as sharp as a razor. I have cut myself more than once using my fingers to smooth the edge of my Structolite and encountering an old piece of furnace cement left over from some other guy.

Furnace cement if fine for the DIY.

Still need to know if my chimney is safe for Santa!

seized123

EdTheHeaterMan said:

Just be careful when removing it next year for inspecting the chimney base.

Well, I don't think in the thirty years I've been in this house anyone has mentioned the chimney and I never thought about it, obviously I hadn't done my homework. Since it's been so long I'll probably get a chimney specialist to look at it. I do know that when I open the little door there's nothing obviously awful right there. Now I'm going to have to learn about chimneys, chimney liners whatever they are ... Sorry, that'll be more questions.

EdTheHeaterMan said:

Still need to know if my chimney is safe for Santa!

My understanding is that nowadays his advanced team checks out every chimney before the Big Guy will consider going down it. I know that I (infected now by tiny bits of knowledge thanks to this website) in his position would not go down any chimney with an oil burner unless I knew CO2, O2, CO, excess air, draft, and that there was zero smoke.

DJD775

EdTheHeaterMan said:

Does this mean that mortar mix is dangerous when applied to my fireplace and chimney bricks. I know some really old masons that have been putting mortar between bricks on chimneys for years. I think the stuff between the bricks on my fireplace and chimney is mortar. Should I have it tested for fire safety? Who would know if it is safe? The fire marshal? The chimney sweep? Maybe the salesman at Home Depot?

What if the Lowes associate disagrees with the Home Depot associate? Will I ever be able to use my fireplace again? And will Santa be safe entering my home this Christmas Eve? What is a person supposed to do?

I'm sticking with Structolite. Problem solved!

I would venture to say that the temperature limit is not a safety issue but rather a potential performance issue when exposed to high heat. What the performance issue is, your guess is as good as mine.

seized123

I have one of those small metal doors below where the flue goes in. Can I use that for annual chimney inspection instead of pulling flue pipe out of the concrete and re-concreting? I know that also one would want to inspect and clean the flue pipes and thimble too, but I’d have to take off the riser and elbow anyway to clean the boiler and could reach in with a long wire brush, easier than breaking free the flue pipe that goes in the thimble.

EdTheHeaterMan

seized123 said:

>I have one of those small metal doors below where the flue goes in. Can I use that for annual chimney inspection instead of pulling flue pipe out of the concrete and re-concreting? I know that also one would want to inspect and clean the flue pipes and thimble too, but I’d have to take off the riser and elbow anyway to clean the boiler and could reach in with a long wire brush, easier than breaking free the flue pipe that goes in the thimble.

Yes.

EBEBRATT-Ed

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.

EdTheHeaterMan

I loved this one:

My understanding is that nowadays his advanced team checks out every chimney before the Big Guy will consider going down it. I know that I (infected now by tiny bits of knowledge thanks to this website) in his position would not go down any chimney with an oil burner unless I knew CO2, O2, CO, excess air, draft, and that there was zero smoke.

Secret Service Elves "advance team" sporting black suites and wearing ear buds while doing combustion tests all thru the fall to make sure the chimney is safe.
(or do they just sit on a shelf near the boiler?)

seized123

Tiny little sunglasses. How times have changed.

realliveplumber

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.

EdTheHeaterMan

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.

realliveplumber

Im not trying to get your blood pressure up. Im trying to help the OP who had a question.


Everything used in construction now a days need to be an approved material and meet a standard. I dont know if structolite does, but I do know before you applied it to a chimney, youd better be sure it does.

I cant find any code that says gypsum plaster is an approved material in masonry construction, specifically a masonry chimney. @EdTheHeaterMan.

Just because thats the way you used to do it doesnt make it right.


The building inspector likes nothing more than hearing "Ive been doing it this way for 30years...... he will smile as he writes out the red tag.

realliveplumber

realliveplumber

realliveplumber

STEVEusaPA

I was hoping @Bob Harper would chime in to give the definitive answer but this discussion has seemed to have gone sideways.

seized123

Interesting discussion though it’s moot for me since I just ended up using the widely available premixed furnace cement which went on very nicely though only time will tell how it holds up. 

If I may ask another question to @realliveplumber and anyone else which is also somewhat sideways of the topic: I notice you cite the International Mechanical Code, which I didn’t know existed, and some other code. If a pro wants to find out what code is for something, what does he do? My guess: check local code, and if it provides no guidance go to the International Mechanical Code, and then work your way down? Is there a national mechanical code? I know one should check the NFPA if it involves fire/combustion, and then would you go to state code (in my case the New York State Mechanical Code)? I’m assuming a case where you really need to know for sure and nobody you ask knows for sure.

realliveplumber

I would check with the local municipal construction department. You would follow the codes that are adopted by the government.

NJ adopts its codes Statewide. They are all available to view on the state division of consumer affairs website. They call it the uniform construction code.

STEVEusaPA

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.

seized123

I'll remember the name, thanks.

Bob Harper

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

realliveplumber

Deepest condolences to your family.

EdTheHeaterMan

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.

Bob Harper

LOL Ed. Yes, the funeral was yesterday. I couldn't resist misbehaving. Actually, she was a very loving, caring person. Her alter ego caused me to give her the moniker 'curmudgeon'. Very conflicted woman.

I've used Structo too. The Structo insulates as it contains perlite in gypsum for a K factor of 1.74- very good I've also used Phil Taggart's "Zip Mix". This is a blend of ChamberTech2000 with a handful of stucco mix thrown in. The lime in the stucco causes a flash set so you have to work fast. Chimney pros use CT2K for parging smoke chambers. 1.5" =5" brick per UL. It passes ASTM C199 as a refractory cement and it contains fiber reinforcing to knit it together. It's very creamy and sticky. That makes it good to 'cement' as in the transitive verb brick to steel as well as gap filling. The bottom line is, the pipe can't fall out. Honestly, if you've introduced it all the way to the face of the flue, how is it going to pull out on its own?

The greatest sin against humanity in venting is where techs will stuff a galvy connector into a rotten hole in the wall and pray the smoke and heat know where to know ignoring the massive caves and gaps they are discharging into. If you don't use a clay thimble or crock, use ss cemented into the wall permanently with the discharge well sealed to the masonry circumferentially using refractory cement. I'd like to see you do that with 3" pipe, which I want to outlaw. If you can't reach in through the pipe and palpate that inner seal or apply more mud then you cannot properly inspect or service it thus it fails the code.

Back to the Structolite- gypsum calcines around 275-356F meaning it begins to change state and break down. If your pipe is going to see temps in this range, it would be advisable to switch to CT2K or similar.

Another tid bit: CMU block problem. When you penetrate a CMU block wall up high, you run into a conundrum. You're supposed to breach the chimney as high as practical while meeting your stated clearances to combustibles. At 9", that means your typical 8" block with a 1/2" mortar joint comes up just short on clearance to a mudsill. It gets more fun. Let's say you use a thimble, which moves the connector to within your clearance. Great! So, what's to worry? Concrete Masonry Unit or CMU, aka 'cinder block' is hollow. The code requires chimneys to be constructed of 4" SOLID masonry units (my caps). Moreover, a thimble through a wall requires a minimum of 12" solid masonry units. Many breachings I see are within one course or 8-9" of the mudsill WITH NO BLOCK FILL! Heat from the connector can rise up through the open cells impinging upon the bottom of the mudsill and pyrolyze it. This lowers the ignition temp. from around ~600F to about 300F. Oops. Those cells must be filled. If you're changing out equipment, take a mirror with light and look up through the cells at the mudsill. If its shiney and grey, replace the wood and pack the cells with masonry. I will admit I usually cheat and pack the cells with rockwool insulation then a base of CT2K zip mix. Just be aware those hollow cells stacked one upon another form a chimney-conduit full of hot air.

FYI, 4" hollow CMU block count as solid while all larger blocks do not. Most 3 hole brick count but 10 hole brick do not. A masonry unit must have min. 75% of its cross-sectional area solid. That means 99% of all CMU block chimneys in America are illegal. If they grouted those cells solid, its ok to use.

Fun stuff.

STEAM DOCTOR

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. 

jesmed1

Bob Harper said:

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.

Thanks for that timely bit of info. I live in a 100-yr-old 4-unit house with masonry chimney and terra cotta flue liner just as you describe. I'm having the chimney inspected on Monday as a possible first step in changing from oil burners to natural gas burners in our boilers. We have a reputable local chimney sweep who will inspect it and tell us whether or not the chimney is in good enough condition to handle the natural gas conversion without a new metal liner. I'm expecting him to say we'd need a new liner. We'll see. Meanwhile, I'm going to check inside the cleanout door for the sand that you mentioned.