Rutland cement or silicone?

slindo said:

I ran into an old post here where someone was questioning Vermont Casting's use of Rutland hi temp cement for seals, and saying most of the other stove manufacturers use silicone. Is this so? Does anyone have any comments on the relative advantages or disadvantages of both?

I know in some fields (like divesuit repair) techs like to avoid silicone because once you use it the surface is "poisoned" for any other cement, so you once you use it, you are stuck using it forever, unless you do a major job of cleaning.

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I've been experimenting with this stuff (edit: Rutland 500* clear RTV silicone sealant) recently, and here are my notes.

Used it for door gaskets in both stoves this fall, and I like it MUCH better than cement in that application so far. Only fired a few times though, and haven't had to clean it out yet, but it can't possibly be harder to clean than stove cement which is a major PITA in my book. Will get back to you on poisoning the surface, but I doubt it's an issue that a small wire wheel can't fix on cast iron.

Used it sparingly to make repairs to my cat combustion chamber, basically as a kind of assembly adhesive to hold the fragile refractory material together while I pinned with stainless wires. I have fired this, then inspected. The chamber gets very hot (maybe 1000*) and cooks the silicone to a fragile crumbly whitish powder with basically no adhesive properties left. But I figured this would happen, so it served its purpose, with no unexpected side effects.

Used it also in a similar way to adhere a fiberglass gasket to the cat itself, a custom repair to correct a blow-by problem resulting from a distorted cat and a failing refractory package. Idea was that if I could get the gasket to stay in place on the vertical metal front of the cat long enough to put the cover and fireback back on, then friction and compression would hold the gasket in place after that. The silicone very sparingly used here as assembly adhesive also worked really well. It cooked off, but the gasket stayed in place until I pulled the cover off the cat again to inspect after several firings. I tried this once before using too much silicone, and the results were not as good -- the stuff expanded when it cooked and moved the gasket. With the bare minimum used, results were much better.

I would consider sealing at least some parts of my stove or insert with this next time it's apart. If it doesn't cook off, it seems to me it would have a much longer useful life, better at absorbing expansion than the cement. But having seen the stuff turn to dust after high temps near the cat, I would like to know more about the temperature at which this sealant breaks down before using it in the very hottest areas of my firebox.

Are you talking hi-temp ($15) or regular ($3) silicone? I assume regular since you say it degrades.

I've seen both suggested by various sources for various uses, but wondering if there is any general consensus out there. For example, on rope gaskets? My impression is that regular would be fine - even if it degrades the gasket should remain in place, no?

branchburner said:

Are you talking hi-temp ($15) or regular ($3) silicone? I assume regular since you say it degrades.

I've seen both suggested by various sources for various uses, but wondering if there is any general consensus out there. For example, on rope gaskets? My impression is that regular would be fine - even if it degrades the gasket should remain in place, no?

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For the jobs I described above, I've been using Rutland 500* clear RTV silicone sealant since I had a partial tube left over from installing chimney liner. I did not see this hi temp stuff degrade with door gaskets -- I don't think you could get that area hot enough -- but it definitely got cooked in the high temps near the catalyst, so I don't think I would use it, for example, on my by-pass damper gasket.

Sutherlands sells a high-temp silicone in their fireplace area that is good to 700 degrees. This more for sealing outside the firebox, like along tile or pipe joints. I would think you would want furnace cement for the inside of a stove.

One thing I will mention is that the mfg of Napoleon stoves told us to use loctite (which is a high temp glue) to hold the screws in around the door bracket on the inside of the Napoleon 1402 door. We had some that were loose. This might be useful in dealing with gaskets if you are trying to get the gasket to adhere better.