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New Gasket Adhesive

EgtsEgts Posts: 27
edited May 2012 in EggHead Forum
I fried my felt gasket and decided to go with a fiberglass seal for a fireplace door that is similar to a Rutland gasket. To glue the gasket down I was looking for something that would with stand 800-900 temps and not be orange. I do not like the orange color of the high temp Permatex. I ended up finding "Mill Pac Black". It's a high temp sealant with a max operating temp of 1050 degrees F (565 degrees C). It's been around for 17 years and is used to successfully sealing direct vented hearth products. Here is some info from the manufacturer. The root formulation of Mill-Pac has been used in Steel-making to seal the continuous caster moulds, damming molten steel and preventing breakouts. Mill-Pac Black was formulated using this original recipe, with slight changes made through Research and Development and extensive testing by a major Hearth Products Manufacturer. Mill-Pac Black is approved as the "Fit for Purpose" sealant, meeting high production standards and suitability requirements for use in direct vent assemblies.

Natural Gas & Propane form acidic by-products as a result of combustion. These acids will accumulate in the inner pipe exhaust; slowly breaking down silicone sealants that are most commonly applied in the field. Mill-Pac Black will resist the effects of the acidic accumulation, providing an integral seal that will thermal cycle within the fastened joint for the intended lifespan of the appliance.

Acidic by-product components of Flue gas condensate are per ULC-S636-95:

HCl - Hydrochloric Acid
H2SO4 - Sulfuric Acid
HNO3 - Nitric Acid
NaNO2 - Sodium Nitrate
HF - Hydroflouric Acid
Mill-Pac Black is comprised of high temperature elemental fibres and ceramic fillers that are encapsulated in a high temperature organic based resin. Mill-Pac Black cures with heat; as heat is applied the sealant will begin to expand and flow into the fastened joint providing a homogeneous high temperature gasket.


Mill-Pac Black has many uses within the Hearth Products Industry:

Firebox enclosure sealant used during production.
Sealing the inner pipe of the direct vent assembly from appliance to exterior.
Sealant suited for pellet vent, as it allows for disassembly for cleaning.
(Note: Mill-Pac Black is not an adhesive. Metal joints must be fastened ensuring the gasket is held in place)

Now I know the nay sayer are going to say that since this is not an adhesive that it won't work. However, I did use it and it worked awesome. After applying a bead I pressed the fiberglass gasket down, started a 400 degree fire, closed the lid and let the grill go for an hour. I then shut it down and 24 hours later it was cured. The gasket is not going anywhere. Best of all I don't have orange spots of Permatex oozing out, combined with a sealant that has a much higher temp rating than silicone.


  • Hillbilly-HightechHillbilly-Hightech Posts: 966
    edited May 2012
    I was also looking around & found this (907GF Severe High Temperature Ceramic Sealant/Gasket):  - this bad a$$ stuff is rated @ 2300* F!!!!

    I'm curious though, whether you use the stuff I found (907GF) or the Mill Pac Black, why not just use it by itself as the gasket? 

    EDIT:  P.S.  it seems that "Mill Pac Black" stuff needs to be heat cured.  The stuff I found (link above) is RTV, though it says that mild heat may accelerate curing.  I'd like to do some more research on both...
    Don't get set into one form, adapt it and build your own, and let it grow, be like water. Empty your mind, be formless, shapeless — like water. Now you put water in a cup, it becomes the cup... Now water can flow or it can crash. Be water, my friend. - Bruce Lee
  • EgtsEgts Posts: 27
    Hilly-Billy, good question. Data sheet wait it would cure and still be flexible. I looked at making a jig to slide around the rim of the base, but I wasn't willing to gamble on how smooth the gasket surface would turn out with just using Mill Pac and how flexible it really would be. My initial guess was that it would be stiffer than silicone with what I've seen ot the HVAC industry. So.....I added the fiberglass gasket. I forgot to mention in my first post that after the Mill Pac was cured I took my propane torch and ran it over the fiberglass gasket to burn off all of the protruding glass fibers on the gasket. While the glass doesn't burn, the individual fiber just burn/melt away. Hope fill this solution will last for quite some time.
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