Is it safe to use cinder blocks or red bricks in stoves and ovens?

As how-to book and blog authors we face many questions that begin, “Is it safe to . . . ?” And, for some reason, any post of ours involving rocket stoves sets off a firestorm of incoming Google hits.

An old blog post on a “Redneck Rocket Stove” made out of cinder blocks prompted many to suggest that the cinder blocks would explode due to heat. Leon, of the blog Survival Common Sense, does a good job of refuting this notion in a blog post, “Build a brick rocket stove: Is it safe to use concrete blocks?” The short answer is that those concrete blocks are not going to explode. But if you want something permanent you should use fire bricks and fire clay as mortar so it won’t crack.

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Related to this issue is our use of regular bricks in the hearth of our adobe oven. Most sources suggest using fire bricks or kiln bricks. Kurt Gardella, the adobe master who led the workshop where we built our adobe oven, is a fan of recycling materials and saving money. We happened to have a pile of ordinary red bricks and he said it would be fine to use them for the oven floor. He was right. We have fired the oven many times and none of the floor bricks have cracked. If I had not had the red bricks on hand and I was at the brick yard buying materials for an oven, I probably would have bought fire bricks. But having just paid for sand and straw gives me cheapskate bragging rights.

Opinions? Have you faced this issue?

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4 Comments

  1. I have no idea exactly what kind of bricks were on my friend’s house that I watched burn with him inside. But, none of the bricks cracked that I ever saw. It seems they were all loose in one area, but it was the mortar that seemed to give way somehow. I did walk close to his house the next day and marveled that the bricks seemed to stand when the wood underneath was charred and some gone.

  2. We used a combination of cinder blocks and regular, recycled bricks for our outdoor maple syrup fire pit last winter, and a few bricks popped apart with a loud noise and incredibly minor shooting out of debris. We also had a cinder block crack. I’m not sure if the extreme temperature differentials are part of the problem (fire vs. sub-freezing outdoor temps), but I certainly wouldn’t go so far as to call it an explosion…

  3. The redneck rocket stove pictured won’t explode, because it isn’t mortared, so there are pressure release cracks. If you build with cinder blocks and mortar the whole thing together, it will probably crack and then settle the first time it gets to high temperatures. This happened with my dad’s home built smoker (a big cinderblock creation)… but it still works just fine, and is happily in use more than 20 years later.

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