Sealant for chimney mount

[David Vaughn]

Some recent rains have found a new way into our cabin. Our E31 has a wood stove. The 3” chimney flue passes through a 5” opening in the deck. The leak is at the base of the wood mount where the exterior cap is mounted. Got it apart and the old sealant is obviously beyond its “best if used by” date. No problem, clean it up and reseal it.

But with what? Normally I’d use butyl tape on deck hardware that is mechanically fastened to the deck, but in this case is temperature an issue? Do I need something more along the line of chimney flashing sealant? Anyone have experience with resealing around a chimney?

 

[Christian Williams]

I don't know the answer, but if it were me I'd probably use some version of standard caulk unless the temperature there gets worrisome high. If so, there are lots of high-temp engine gasket products, Permatex and so on, for peace of mind.

 

[Kenneth K]

Many chimney pipes are double-walled to keep the outer wall cooler. If yours isn't, that might be one thing to consider. The fact that the pipe is surrounded by wood gives you a good idea that heat isn't a huge problem. The teak would likely be burned/dried-out/cracked if it were.

I wouldn't recommend chimney flashing sealant unless you can find one that remains flexible. I used hi-temp flashing sealant on my home's dryer vent and it dried rock-hard--probably not good for a boat.

You could try any number of high-temperature silicones or automotive RTV's--but silicone always has the problem that it permeates gelcoat, preventing any type of non-silicone sealant from ever adhering there again. But, if silicone is what was already used, you may as well use it again.

Or, you may want to just check for the acceptable heat ranges or various common sealants. Sikaflex says it's good up to 70 degC/158F, while 3M 4200 is good to 88C/190F.

For any sealant that comes in direct contact with the hot metal, I'd definitely use high-temp RTV.

 

[David Vaughn]

Thanks guys. I’ve got some 4200 left over, I’ll give that a try.

 

[Nick J]

Now's a good time to seal the core. The chimney on our 25+ was one of the sources of water that caused core damage. It's fairly easy to hollow out and fill with epoxy or replace with G10.

 

[David Vaughn]

Good point Nick, but the guy that put the stove in however long ago, beat me to it. Core is well sealed all around the opening.