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Metal lined Plywood?

post #1 of 6
Thread Starter 

I am making a small, inexpensive pit for direct heat charcoal grilling. My son passed through Memphis and fell in love with Rendezvous ribs, so we are looking to cook at 350 18" over the coals (we will start at 18", but the height is adjustable to find the perfect distance for holding 350 at the grill on this contraption). I got an old New Braunfels Red River charcoal grill and separated the ash pan from the lid. The ash pan goes on bricks inside the cinder block sides that the lid sits on. The sides go up against my fireplace chimney which provides the back. All I need is a door or doors for the front. Being on a tight budget, I want to use a piece of 3/4" plywood I have for the doors and simply line it with whatever tin or thin sheet metal I can scrounge. As long as I line it with metal, I am thinking that the plywood will be protected from the flames and should never pose a fire threat. What do you all think? Anybody have experience with this sort of thing?  Thanks!

post #2 of 6

Sounds risky. The plywood could warp, delaminate, outgas unpleasant vapors, etc.

post #3 of 6

pulled this off the web

Thermal Degradation and Ignition Point

When the temperature of dry wood is raised above 212° F (100° C) a slow exothermic decomposition takes place. This degradation involves the loss of carbon dioxide and volatile materials such as extractives, in the form of gases or vapors. The rate depends upon temperature and air circulation.

The thermal degradation and ignition point of wood and plywood may be generalized by the following:

  • 230° to 302° F (110° C to 150° C): The wood will char over time with the formation of charcoal. If the heat is not dissipated there is some possibility of spontaneous combustion. Examples of the thermal degradation of maple blocks are:
    • 1050 days at 225° F (107° C): 10 percent loss in weight and slight discoloration.
    • 1235 days at 248° F (120° C): 30percent weight loss and a chocolate color.
    • 320 days at 284° F (140° C): 60percent weight loss and charcoal appearance.
  • 302° to 392° F (150° to 200° C): Charring takes place at a somewhat greater rate. If the heat source is close to the wood, the surface temperature may be higher than the temperature of the surrounding air due to radiant heating. Gases released at these temperatures are not readily ignited by an outside flame source. A greater chance for spontaneous combustion is present if the heat is not dissipated.
    • In tests, after 165 days at 302° F (150° C) maple blocks showed a 60 percent weight loss, and the samples had the appearance of charcoal.
  • 392° to 536° F (200° to 280° C): The formation of charcoal takes place at a rapid rate. Spontaneous combustion is probable.
  • 536° F (280° C) and greater: Spontaneous combustion will occur in a short period of time.

A number of attempts have been made to measure a definite ignition temperature of wood, with little success. A specific temperature is hard to define because there are so many contributing factors, such as size and shape of the material, air circulation, rate of heating, moisture content of the wood and so on. Estimates range from 510° to 932° F (270° to 500° C), but no value should be accepted as an absolute.

 

copied from    http://www.performancepanels.com/thermal-properties

post #4 of 6
That would also play into why wood gassifier can run engines. Personally I would not do a wood smoke house for anything beyond cold smoking. You can wood frame something then insulation barrier between the wood and inside wall paneling. That would be fine for heat then based on your insulation.
post #5 of 6

Also if you are going to operate at 350* that is the air temp at the cooking grate.  The actual temps near the heat source will be much higher.  The metal will give absolutely no protection from the transmission of that heat to anything the metal is in contact with.  You might be able to do this with an air gap (ie, two sheets of metal  or the box within a box concept where there is air or insulation between the two boxes), but at that point you are basically building a metal insulated smoker with a plywood exterior so why bother with the plywood.

 

It might work for a while, but I don't think it would last very long and stands a good chance of the wood combusting at some point.

post #6 of 6

This is what I picture in my mind with wooden build smoke houses that are not lined. I think this one added more smoke to the cook then the owner intended.

 

 

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