Jeanine Gurley wrote:I also want to build a pit but hubby told me not to use anything with concrete - such as cinderblocks. He said they can shatter/explode suddenly with high heat and temp changes. Others may have used them just fine but since he was a concrete man by trade for many years I'm going to trust him on that one.
I knew about the risk of degradation over time with concrete (the lime in it powders at high temperatures), but I didn't run into the explosion issue until recently. I think it's the aggregate (rocks) in the concrete that actually explode, but it's pretty impressive to watch. Hard to tell what aggregates they used in an old cinderblock, but at least they're usually smaller than the rocks in a 6" slab. We had glowing chips leaping about 8-10 feet when we tested our new super-insulated rocket core.