32" build in Calgary, AB - pompeii neapolitan

[Giovanni Rossi]

I appreciate this dialog. My gasket is not showing physical signs of breaking down, which makes sense as the temps are not that high. But, off gassing occurs at much lower temps.

It looks like the better option would be LavaLock RTV650.

Once I get my v2.0 insert made I'll experiment with no door gasket and with the LavaLock and record both the door temps and heat retention over time.

It may be that a door gasket does not provide a material improvement.

I'll report the findings on my build thread.

[IH123]

I appreciate this dialog. My gasket is not showing physical signs of breaking down, which makes sense as the temps are not that high. But, off gassing occurs at much lower temps.

It looks like the better option would be LavaLock RTV650.

Once I get my v2.0 insert made I'll experiment with no door gasket and with the LavaLock and record both the door temps and heat retention over time.

It may be that a door gasket does not provide a material improvement.

I'll report the findings on my build thread.

This Silicone is not an insulator. It will conduct heat:

fibreglass: R-Value (Per Inch)Roughly R-2.2 to R-4.0 (depending on compression density)

LavaLock RTV650: R-Value Negligible (Solid silicone transfers heat quickly via conduction)

[david s]

This Silicone is not an insulator. It will conduct heat:

fibreglass: R-Value (Per Inch)Roughly R-2.2 to R-4.0 (depending on compression density)

LavaLock RTV650: R-Value Negligible (Solid silicone transfers heat quickly via conduction)

Conductors and insulators are relative. R values are calculated as the reciprocal of conductivity values.
Silicone is not particularly conductive.
Check the Engineers toolbox for conductivity of materials.

eg.

Perlite 0.03 W/(mK)
Silicone 0.2
Timber 0.15
Firebrick 0.47
SS 304 14.4
Carbon steel 59.0

so while silicone is 6X more conductive than perlite, carbon steel is 295X more conductive than silicone.

https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html#gsc.tab=0

[IH123]

	Heat Loss at 600°F Inner Temp	Heat Loss at 800°F Inner Temp
3/16" A36 Carbon Steel	~882,000 BTU/hr·ft²	~1,134,000 BTU/hr·ft²
1/4" LavaLock RTV650	~3,675 BTU/hr·ft²	~5,060 BTU/hr·ft² *(will break down)
1/2">>1/4" Compressed Fiberglass Rope	~880 BTU/hr·ft²	~1,520 BTU/hr·ft²

	Thermal Conductivity (k) at 600°F
3/16" A36 Carbon Steel	44 – 46 W/m·K
LavaLock RTV650 Silicone	0.2 – 0.3 W/m·K
Fiberglass Rope Gasket (1/2" compressed to 1/4")	0.05 – 0.07 W/m·K

heat loss compared to the steel door at 600F is:

silicone gasket: 240 times less
fiber glass rope: 1002 times less


which is actually about x4 not even x6 if pure perlite

[Giovanni Rossi]

Hey fellows, sorry to have opened this can of worms and to have temporarily hijacked this thread. I'm not sure the magnitude of the differences are all that material to this application.
I'm going to make this my final post and then sign off from commenting on this build in the future.

I shared the gasket solution as it made sense for me and has worked well and I thought it was a good alternative to a rope product that I had tried and discarded because of shedding fibers.
I was happy to have been cautioned on my choice of material and that led me to research a better alternative.

Choices made:
I was trying to solve what I perceived to be an issue in my particular situation.
While I was getting great heat retention with just the steel door, I wanted to push that as far as I could for multiday cooking.

My steel door is designed in such a way that it needs to be tilted to pass through the exterior arch. This made it impossible to add any thickness to it if I wanted to try to insulate it.
This led me to the idea of a separate slide-in insert. Again, I was intrigued by the history of using wooded doors. My insert is a wooded box with insulation inside.
My lack of knowledge led to an early failure that I have learned from.

The issue with an insert is that it needs to be sized so that it doesn't bind in the arch due to expansion of the wood as it heats or the contraction of the arch when it cools.
Accounting for this means there is a small gap around the sides and top that heat can escape from.
Since the steel door doesn't fit tightly against the inner arch due to slight variability in the bricks and mortar joints, I was looking for a substance that would remain flexible and tolerate the high temps.
That's how I landed on the silicone gasket.

While I am going to try another product, and may decide it is of little additional value, I'm honestly not that concerned using the gasket in my application.
While the top of the dome far exceeds 1000^oF during a pizza session, once the dome comes to equilibrium, the internal wall of the dome never exceeds 550^oF.
I can't remember exactly, but any time I've shot the exterior of the inner arch, I believe it's somewhere in the 300's.
If there is any off-gassing, I'm hoping those substances will follow the warm air up the flue.

IH123, good luck on the rest of your build. I will follow from afar since I make it a habit to read every post on the Forum.