I have chipped a lot of stuff that looked like that. It needs to be sawn or bifaced before cooking, else it will most likely blow up. I agree that it needs a preheat temp of 190-210 degrees F before beginning to ramp up. I think it will take 500 degrees to get very agreeable. Hold it there for 3-4 hrs or a whole day before ramping down.
Instead of ramping, I put sand under, around, between and over the rocks when placing them into the cooker. The sand is excellent for ramping the temp down for me. In other words, after cooking at the top temp, I just turn it off and the sand prevents any fast ramp down. It usually takes at least 16 hrs before I can touch the rocks.
To do the cooking, buy a turkey roaster for $25 at Walmart. Take the liner out. Drill holes into the lid at various places to allow insertion of a meat thermometer. Wire some fiberglass insulation to the inside of the top cover. When loading the cooker, keep in mind that around three sides (not the side with the regulator) the temp will be 50 or more degrees above the temp of the rest of the inside. Put the toughest stuff there. Do NOT depend on the temps printed on the control dial. Insert a meat thermometer. Be sure it is a thermometer that can go to your target temps. Do not open after starting the cook until the temp is down to 120F or lower, else the rocks may fracture when fresh air hits them. If they have been sawn, be sure to soak them in soapy water for a few hours or overnight then wash them thoroughly.
If the rocks were recently wet, be extra careful that the preheat at below boiling temps is adequate to dry the rocks thoroughly.
PM sent.
WA
