High temp silicone

[maxed_out]

Nice forum, been reading for about a month so time to join in. Does anyone have a recommendation for a high temp silicone? I'm going to clean the chimney and in the process need to reseal the block off plate. Our woodstove (VC circa 1990) is connected to our fireplace hearth. I've used stove cement in the past but just thought I'd ask about new stuff...any experiences/performances would be helpful too. Thanks in advance.

 

[begreen]

Welcome. Just to be sure is this the chimney cap block off plate or the damper block off plate? I've used regular GE Silicone adhesive for this with good success, but it is not in contact with the pipe, just the top plate seal to the chimney cap. If you want high temp, then a good RTV silicone sealant will work. But again, that is not for contact with the liner.

 

[Chad S.]

Kind of a hi-jack here sorry.
When sealing the storm collar to the chimney outside the roof is vulkem flashing caulk good enough or will I have to use rtv? I don't understand what "mastic" is in my instructions. Mastic to me is what holds tile on to walls not seals flashing.

 

[maxed_out]

Thanks for the replies....I havent got to the top seal for the chimney yet but thats good advice, so far I'm just dealing with the blockoff plate that replaces the damper. Its the ole stove to stainless liner-thru the fireplace damper setup.... the vc encore has 8"oval outlet that fits just perfect thru the now removed fireplace damper.

I've used fiberglass to make a "seal" but was looking at switching over to kaowool. I'm wondering about silicone for the edges of the blockoff plate. I've used stove cement before but wanted to try something more flexible. I guess I could use rtv and see what happens. Thoughts???

 

[BrotherBart]

I used plain old 100% silicone from ACE Hardware for the edges of the block off plate and for the top plates on both chimneys four seasons ago and it looks like the day it came out of the tube. And I burn these suckers hot. I am the guy around here that says 100% silicone is 100% silicone and anything else is marketing BS. It and RTV branded stuff both vaporize at 800 degrees and if the edge of that block off plate gets to 800 I will have been far away in front of the house waiting on a fire truck for awhile already.

But buying the nine buck red stuff isn't exactly a budget buster either.

 

[bren582]

I can tell you from experience to follow BB's advice and keep the silicone including the high heat bologna away from the liner and stove connection. Anything silicone based in that area will burn off with a nasty burning plastic smell. Even Rutland's "Seal-It-Right" product which is rated to 800deg F will not hold up and stink to high heaven. Use High heat mortar or furnace cement around the pipe or better yet take the time to line up the connections at the stove collar so you don't need anything or maybe just a bit to seal it up tight..

 

[tradergordo]

Any silicone will work for just about any type of sealing or adhesive around the stove and chimney as long as its in a place that isn't going above 400 °F. Normal silicone sealant is also excellent for gasket rope installations (despite the fact that it goes way over 400 °F). Just buy the cheap stuff from your local hardware store, or the $2 version from Harbor Freight:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90026
which is supposedly good to 600 °F continuous.

 

[maxed_out]

Thanks for the nice replies. you all convinced me to try plain silicone from the hardware store. I'll do that and report back results. I'll also get some numbers for the temp on the plate when shes running as well.