Information About Melting Gaskets

First of all, let us explain what this page is and is not. This page addresses the question of what damages and melts gaskets so that they stick together, welding the cooker shut. It does not address the supposed issue of gaskets pulling loose from the ceramic due to the failure of the gasket adhesive. Although there are stories going around now that the gasket adhesive needs to set through a series of low-temperature cooks before attempting high-temperature cooks, we have never seen this recommendation come from Big Green Egg. The only recommendation we have seen is that when you install a new gasket, you should wait 24 hours before using the cooker. This comes from the gasket installation instructions. We have followed this advice and have never had a gasket come loose. (Well, ok, we had one episode where the gasket came loose after we had welded the dome shut with a mighty flashback that melted the gaskets together. Our efforts to pull the dome open did ultimately rip the gasket loose, but it took a mighty effort.)

So, we wanted to take a look at the issue of gaskets sticking together by actually testing some of the theories and actually measuring the temperatures that the gaskets are exposed to. The primary theories are that various types of high-temperature cooking will melt the gaskets, specifically the Trex Steak method, and cooking pizzas with a pizza stone that is too large.

Is It The Trex Steak Method?
One theory is that the ceramic gets so hot from the temperatures used in a Trex steak cook, that the gasket melts. We don't think so. We conducted a test where where measured various temperatures during a simulated high-temperature Trex Steak cook. Here are the locations we monitored and the type of measuring device used:

Dome Tel-Tru LT225R 150-750 degrees 5" Stem dial thermometer
Ceramic near opening Thermoworks 303-030 Type K Precision Surface Probe, 932 degree max
Gasket interface Thermoworks 113-363 Fine Gauge Wire Probe, 482 degree max

The ceramic temperature was measured with a surface probe in the location shown in the follow photograph by the yellow dot. The gasket interface was measured by placing wire thermocouples between the two gaskets at approximately the 7 and 10 o'clock positions:

We measured the temperatures at 1-minute intervals for 50 minutes, simulating the Trex process of starting the fire and getting up to 700+ degrees, searing for 3 minutes on each side, lowering the temperature to 400 degrees and waiting for 20 minutes for the steak to rest, followed by 13 minutes of roasting at 400 degrees. We won't bore you with all 200 readings, but here are the readings taken at the various significant events during the process:

Event Time Dome Surface Gasket 7 o'clock Gasket 10 o'clock
Startup 0 < 150 71.1 73.1 71.6
Searing Temp Reached 8 700 81.5 104.9 99.1
Steaks go on 10 740 88.1 120.9 110.9
Steaks flipped 13 680 113.2 152.3 137.8
Steaks come off 16 710 132.3 171.1 160.0
Vents shut 17 650 147.6 181.1 168.0
End of 20-minute rest 37 395 180.1 209 185.0
End of 13-minute roast 50 390 185.4 217 187.7

Temperatures reached during a typical Trex Steak cook. Note that the searing and
roasting times used were towards the upper end of what you might realistically use.
This was done to demonstrate the worst case possibilities.

As you can see, the highest temperature reached at the gasket interface was only 217 degrees. The manufacturer of the gasket indicated to Big Green Egg that the gasket will tolerate temperatures up to 1100 degrees. So clearly, the Trex Steak method will not, in and of itself, damage a gasket.

Is It The Pizza?
The next theory that we'll look at is that cooking pizza on the Egg at temperatures such as 550 degrees will melt the gasket. Also, there is a sub-theory that using a 16" pizza stone instead of the "recommended" 14" stone will force hot air around the stone and against the sides of the cooker, again somehow melting the gasket.

To look at pizza cooking, we will again use the thin wire thermocouples to measure the temperature at the gasket interface, but this time we will also add a Thermoworks WD-08467-64 K type high temperature ceramic probe good to a maximum of 2500 degrees. The probe was positioned just inside the cooker where it could measure the temperature of the air rising up the inner wall of the cooker.

Gasket after many 1000-degree cooks
The gap left when using a 14" stone.
Gasket after many 1000-degree cooks
The gap left when using a 16" stone.
Gasket after many 1000-degree cooks
The high-temperature ceramic probe inside the cooker.

We did two measurements, one with the 14" stone in place, and then one with the 16" stone in place. We allowed the 14" stone to preheat at 550 degrees for 30 minutes. We then allowed things to cool off a bit when we removed the 14" stone and replaced it with the 16" stone. We then allowed the cooker to come back up to 550 degrees and allowed the 16" stone to preheat for 30 minutes. Here's the results:

Stone Size Dome Surface Gasket 7 o'clock Gasket 10 o'clock Inside
14" 550 260 407 429 753
16" 550 301 475 475 767

The fact that the surface and gasket temperatures increased between the 14" and 16" stone tests should be no surprise since the ceramic material kept getting hotter and hotter over the 90 minutes that we had the cooker going for this test. However, the inside temperature remained about the same, dispelling the theory that the larger stone channels hotter air to the sides of the cooker, resulting in melted gaskets. In fact, as you can see, the gasket temperature never got over 500 degrees, and again, the gaskets are supposed to be able to withstand 1100 degrees. So, no it isn't the pizza.

Is It The Warmup?
We did happen to observe something which might prove useful in avoiding gasket damage when cooking pizza. In the table above, you can see that the temperatures of the gasket, the ceramic and the air just inside the cooker don't get all that hot when the cooker is sitting stable at 550 degrees. But what about as you are heating up the cooker? During that time, you have a hotter fire going than when you have the cooker stabilized at 550 degrees. With the 14" stone in place and vents wide open as we heated the cooker up, we observed that the temperature just inside to cooker was 980 degrees. This is approaching gasket-damaging temperatures, so we then placed the daisy wheel top on the cooker with the slider all the way open. The temperature just inside the cooker dropped to 780 degrees, perhaps a more comfortable range. So, it might be adviseable to place the daisy wheel top on the cooker when heating it up for pizza with a pizza stone in place. You can trade a slightly longer warm up time for lower temperatures near the gasket interface.

We repeated this little experiment with no plate setter and pizza stone, to recreate what happens if you are just heating the cooker up to nuclear temps for searing steaks. With the daisy wheel off the cooker, when the dome temperature reached 950 degrees, the temperature just inside the cooker at the gasket interface was 690 degrees. We then placed the daisy wheel on the cooker with the slider all the way open. The dome temperature fell to 860 degrees while the temperature just inside the cooker crept up to about 700 degrees. So, there was really no drop in temperature just inside the cooker when we placed the daisy wheel on the cooker as there was with the pizza stone/plate setter in place. This shows that the pizza stone/plate setter does indeed force more heat to the perimeter of the cooker. And while it might benefit your gasket to heat the cooker up for pizza with the daisy wheel in place, it doesn't make any difference for heating the cooker for searing purposes.

It Isn't Just High-Temperature Cooking
So, the Trex Steak method doesn't produce temperatures high enough to melt the gasket, and an hour and a half of pizza temperatures with a plate setter and pizza stone in place also didn't produce gasket-melting temperatures. As one final bit of evidence that hot ceramic is not the cause of melted gaskets, let us show you what the gasket looks like on our medium Big Green Egg. This is the gasket after several years of using this cooker to conduct our maximum temperature tests for the Lump Charcoal Database. In this test, we load the cooker up and let the charcoal burn as hot as it can for up to 10-15 minutes. The temperatures routinely exceed 1000 degrees. However, we never open the cooker when it is burning this hot. When the test is over, we always close the bottom vent and place the ceramic top back on, so that the gasket is not exposed to either a flashback or just the normal outpouring of heat which occurs when you open the dome. The lid on this Egg seats properly and there are no leaks anywhere around the circumference of the opening. Here's what the gasket looks like in four locations around the perimeter of the cooker:

Gasket after many 1000-degree cooks
Gasket after many 1000-degree cooks
Gasket after many 1000-degree cooks
Gasket after many 1000-degree cooks

Photos of the gasket from our medium Big Green Egg after many 1000-degree cycles.

As you can see from the photos, while the inner portion of the gasket has darkened considerably, most of the gasket is still in good shape. You can see the individual threads of the gasket material. Obviously, there is no melting of the gasket material going on here.

Is It The Gap?
So what does cause melted gaskets? For the gasket material to get hot enough to melt and bond, the surface of the gasket has to be exposed to heat on the order of 1100 degrees. As we have seen, this just doesn't happen due simply to cooking at high temperatures. In order for temperatures this high to even have a chance to get to the gasket surfaces, the gaskets cannot be touching each other so that hot air can pass between them. One way this could happen is if the dome and base aren't properly seated leaving gaps between the two gaskets:

Properly seated gaskets with no gap. Hot air stays inside the cooker.

Gaskets with a gap. Hot air can move between the gaskets and exit the cooker.

So, to examine the effect of a gap between the gaskets, we created a gap on one side of our large Egg so we could measure the temperature in the gap as well as on the other side of the cooker where there was no gap. As you can see in the photo below, on the left side of the cooker is a Thermoworks 113-383 high temperature wire thermocouple with fiberglass insulation which is in contact with the gasket when the lid is closed. On the right side of the cooker is the same type thermocouple that rested in a gap between the gaskets formed by place two nails between the dome and the base:

Gasket after many 1000-degree cooks
Setup for gap temperature testing

The first thing we did then, was measure the temperatures as the cooker heated up to 900 degrees as you would when preparing to sear steaks:

Dome Left Gasket Right Gap
200 78.9 74.8
300 87.4 80.0
400 89.4 80.8
500 92.5 81.2
600 96.4 84.3
700 101.8 88.6
800 107.1 93.3
900 115.0 99.0

What's this? The temperature in the gap is lower than the temperature where the gaskets meet? Well, yes that makes sense. While the cooker is heating up and there is a strong chimney effect going, air is being pulled through the gap as well as from the bottom vent. The cool air from outside the cooker being sucked into the gap indeed keeps the temperature between the gaskets lower than where the gaskets touch.

However, that's not the whole story. We then placed the daisy wheel on the cooker with the slider open to simulate the conditions when you are maintaining a high temperature for a long time, such as when cooking pizza. Here's what we saw:

Time Dome Left Gasket Right Gap
1 650 132.7 129.2
2 650 141.8 134.9
3 680 151.3 149.9
4 680 159.9 162.1
5 680 170.7 228.0
6 650 180.8 241.7
7 660 191.5 259.5
8 700 201 279.0
9 660 210 301.5
10 680 219 312.9
11 670 227 320.4
12 670 235 335.4
13 680 242 342.2

So, as you can see, the temperature between the gaskets just kept slowly increasing as time passed, while the temperature in the gap jumped up quite a bit and rose to a temperature 100 degrees greater than the temperature where the gaskets touched. Once the cooker was at a stable temperature, air was no longer being sucked into the cooker in such volumes that it was keeping the gap cool. Another interesting observation which reinforces this idea that air being sucked in or forced out makes a big difference in the gap temperature was when we placed the ceramic cap on the cooker to shut it down. The temperature in the gap suddenly spiked to 366.7 degrees as the only way for air to exit the cooker at that point was to go through the gap. When we then closed the bottom vent, the gap temperature dropped to 295 degrees, since air was no longer able to pass through the cooker. And while we were doing this, the temperature where the gaskets were touching slowly climbed to 271 degrees, peaked and then slowly fell as the cooker cooled off.

There are also reports of "wavy" domes/bases where the surfaces aren't in a plane and thus cannot mate properly all the way around the perimeter of the cooker. Of course, this would also create a gap that could let hot air out between the gaskets. However, based on our observations, it doesn't appear that even a gap between the gaskets will produce temperatures that melt gaskets.

Is It Burping? (Excuse me!)
Of course, the other time that the gaskets aren't touching is when you open the cooker. We can verify that a large flashback will melt a gasket (we did it on our very first cook on the Egg), so avoiding flashbacks is one way to avoid melted gaskets. However, one method to avoid flashbacks that is often recommended is to "burp" the Egg. In other words, to raise the lid an inch or so and induce small flashbacks. These small flashbacks, while not as scary as large ones, still produce extremely high temperatures. Carbon monoxide, one of the gases that burns in a flashback, will burn at about 1100 degrees, enough to damage the gasket. We obviously don't have the equipment to measure the momentary burst of heat caused by a burp (excuse me!), but we recommend against burping the Egg.

Instead we advocate opening the vents for 10 seconds or so in order to get the draft going again and to allow any collected flammable gases to escape before you open the cooker. Then, slowly open the Egg and inch or so for a couple of seconds, then raise the lid. This should avoid any gasket-melting flashbacks, and reduce the volume of hot gases exiting the cooker over the gaskets. In general, we think that any time you open the lid with a hot fire going, you want there to be a good draft going through the Egg so that hot air isn't inclined to be forced out between the gaskets when you open the lid. If the air is passing through the cooker unimpeded, then little if any pressure will have built up inside the cooker to force air out between the gaskets.

Is It The Adhesive?
One last theory we have heard is that if your gasket is new, the adhesive can soften to the point of liquifying and then soak through the gasket until it reaches the gasket interface. Once the cooker cools down, the adhesive sets and you now have two gaskets glued together. We haven't determined a way to prove or disprove this theory, but like we said earlier, Big Green Egg has never warned of this and we have never observed it in over 6 years and several gasket replacements on several cookers. We just don't believe this one, for what that's worth to anyone.

So, we are sorry that we haven't produced evidence of a smoking gun, but based on everything we have observed, the only time that gaskets are exposed to temperatures that will melt a gasket is during a flashback. But in general, it probably makes sense to

  • follow Big Green Egg's instructions when installing gaskets,
  • eliminate gaps between the gaskets caused by ill-fitting lids, and
  • avoid flashbacks and avoid burping (excuse me!) your cooker.
We wish you good luck with your gaskets!       Home       Search Our Site       Email The Whiz       Listen To Whizcast       Whizlog       Buy Whiz Gear       Privacy Policy       Kamado Grille
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