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Marcel 10-20-2005 06:53 AM

#61 Furnace Caulk is not "adhesive"

(M) I will be joining sections of clay pipe chimney liner. I've read on this forum that stove/furnace cement is very strong and would like to use it. But at Home Depot, the 4 different "3M" products they offer, while implying an adhesive quality, are listed as "caulk".:confused:

(M) If you have used any of the following "3M" products on your chimney, please tell me which of the following:

FB 136, FD 150+, 1C 15WB, CP 25.

(M) If you have used something different, other than the refractory mortar specified in the Forno Bravo instructions, please let me know what that product is.

(M) btw, I am never quite sure which of these forums is the correct one for a question like this, since "Pompeii Oven Construction" could also apply.



svtlightning 10-20-2005 12:52 PM


I used "Harvey's Furnace Cement", found it in the duct work section @ HD.
The 3M products were alot more expensive.

My liner sections are 2' and did not have to join them. I used the "Cement" to join the liner to the angle iron supports.


Marcel 11-13-2005 08:58 AM

Joining short chimney liners, Furnace cement, & foil

(M) I saw Tarik's photos at the following URL and guessed that like me, Tarik could only get short sections of flue liner. Tarik's oven is similar to mine in concept and he also seems to be building a "gable house" around his oven with metal studs.

(M) I have 2 comments about joining the clay liners: We will need probably at least 4 of 1 foot each liners stacked in order to clear a peaked roof. The question I have is how to secure each 1 foot section to the next?

(M) I tried "Rutland" Chimney Sweep Furnace Cement, a gray water based high Temp. resistant adhesive that is said to dry hard. I patched between two liners with the product straight from the container. It is supposed to harden in an hour. The next day it was still soft and pliable! I will use it as a sealer but not as an adhesive.

(M) I have no photos yet to support my next idea but I hope to post some when I'm at that point. I plan to cut 4 pieces of 5 foot re-bar. Each piece will be refractory mortared to the inside corner of the existing first (bottom) clay liner. After that mortar dries I will still have 4 feet of re-bar sticking above the first liner. Then I will apply some mortar to the next liner's corners and with the aid of a ladder, slip the 2nd liner on top of the first. I will have already applied the Rutland Furnace cement to the horizontal edges to insure a tight seal. I will be able to add additional mortar to the inside corners once the new clay liner is over the re-bar, by using a long and narrow trowel. This will allow me to imbed the re-bar in the corner mortar.The object is to make one clay liner out of the 4 or more pieces. Any re-bar that extends after the last liner is secured will be cut to size with my angle grinder.

(M) As to securing the entire clay liner, I have an existing "keystone" at the top of my dome. I will use it and a steel rod to extend to the 2nd or 3rd liner and secure it as well with mortar. The top two flue liners will be secured with metal stud collar ties, and then in between the metal studs of the roof joists.

================================================== =====

(M) On a different point; I had difficulty getting the perlcrete insulation to adhere to the aluminum foil that covers my dome. I plan to build a simple plywood and 2x4 flexible jig to retain the perlcrete as it is drying. That form -jig will be built today. Next week is supposed to be rain free so by Tuesday I hope to test the form. I'll post photos when I get access to a digital camera.



paulages 11-13-2005 10:30 AM

good luck with the dry window marcel. godspeed.

i actually made pizza for 30 people two nights ago in an absolute gale, and stayed perfectly dry! i have glass covering the 3 foot space between my back porch and the oven, sitting on top of the kiwi arbor. it's great to feel like i've "beat" the winter rain, and will be able to use it all winter long. i also got it up to proper temperatures for the first time in a while.

you might consider framing your structure this week, and having a temporary decking up for the roof, so you can throw a tarp over it and still work in light rain. you can always continue with the chimney when you have more dry weather, but having the structure roughly ready to go might give you a bit more security.

Marcel 11-13-2005 03:08 PM

Oven has taken 3 test firings successfully
# 75

(M) Paul wrote:

(P) ..."but having the structure roughly ready to go might give you a bit more security."

(M) Perhaps I forgot to post my test firings of a few weeks ago which were successful, so I actually already have the structure roughly ready to go. But unlike Paul, who has a rain free breezeway, my oven necessitates a walk in all weather to start baking. I've not actually tried a pizza yet because the 3rd firing was only a medium flame and I want to continue to gradually bring it to "Farenheit 451".

(M) Because it was simply gray and not raining, I tried my "jig" aready today to retain the perlcrete. It was only moderately helpful since the circumference of the dome determines a rapid increase in perlcrete cladding against a flat surface. However, I got more of a feel for applying the perlcrete with a flexible wide putty knife. I was able to build up perhaps 1/10th of the area with perlcrete. When it dries and hardens (please, please!) the chicken wire will be secured enough that I can bend &/or cut the extra and more easily continue. Once past the vertical I should be alright. I will try other builders method of hand packing with rubber gloves on.

(M) I need to keep reminding myself that this project is supposed to be a process; enjoyable in itself and that I am in no hurry to finish it.



paulages 11-13-2005 05:05 PM


Perhaps I forgot to post my test firings of a few weeks ago which were successful, so I actually already have the structure roughly ready to go.
i was talking about the encosure, which will keep your oven dry, but while on the subject...

why not build an entire pole-framed roof, which extends well beyond the oven in all directions, giving you a rain-proof structure to stand under in the winter? it would be easy to construct: much like a carport or any other open-air roofed structure. the roof of the structure could still be the roof that sits on top of your upright walls containing your insulation, but would give you year-round coverage. face it---we don't have quite the weather freedom many other people may have. i believe i remember someone on here having such a strucure for their oven, where the oven ties into a larger awning. it wouldn't really be much more expensive than a smaller roof, and the pole-framing would take the weight off of the actual enclosure.

Marcel 11-13-2005 05:39 PM

Extend a roof to use the oven year round

(M) Thanks, Paul for your concern and idea to cover the oven with an extended roof. I'll run this by Mary to see what her reaction is. Because I would like a fairly steep roof, the eaves sides might be left out of the plan or the roof would be too low, but extending the as yet to be built enclosure roof would give us some protection from the elephants and is indeed an easy build.



paulages 11-13-2005 06:06 PM

my suggestion, would essentially be a big lean-to roof, with the oven tying in to enclose the insulation. 4 poles, some basic framing, and as easy as it gets roofing. maybe not totally traditional looking, but it does leave your finishing options for the oven itself a little more open, much like an indoor oven.

Marcel 11-14-2005 07:07 AM

Some "furnace cement" needs to heat cure.

(M) I phoned Rutland about the still flexible "Furnace Cement"; their Item # FSC32. Apparently I bought the wrong product for joining clay liners. What I bought needs to heat cure, and at fairly high temperatures not generally attained at the top of a chimney flue. The product I bought is best used for sealing and joining metal to metal, or metal to brick.

(M) What I will need to use is a refractory mortar, the same as, or similar to the mortar I used to set the firebricks in my dome. :confused: Those proportions were 8 parts mason's sand, 3 parts Portland cement, and 2 parts fireclay ("greenstripe"). I may cut back to 6 parts of mason's sand for assumed greater strength with a thinner bead but a civil engineer could advise me if the revised proportions for joining clay tile liners to each other would be better (stronger) than the standard refractory mix. Since the temperatures are lower in the "chimney" than in the oven proper, cracking is less of a concern than strength.



aikitarik 11-14-2005 11:39 AM


I was about to post about the furnace cement. It is intended to be cured with high heat, and I've been using it in the cracks that I've made in the oven with great success. It's always an excuse to fire up and cook.

The whole idea of the aluminum foil to to prevent the insulation from from sticking to the oven when you pour it. I've poured about 5 large bags of perlite concrete over the oven now, using a retaining form of 1/8" masonite.


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