How can a cinder block be made easier to break for a demonstration? I have heard of different ways, but much is basically "cooking" / "drying" the cinder block in an oven. If this is true, what temperature is used and usually for how long? Thank you for any help you can give me in this topic.
Bricks and cinder blocks are relatively easy to break since, as with most martial arts breaking, they are broken by exploiting their weakness, not their strengths. The strength of bricks and blocks come from their compression strength when stacked. They are not intended to be supported at the ends while having force applied to the midpoint of the span. Bricks and blocks gain strength from their aggregate, not from their base material. Bricks contain sand, cinder blocks contain cinder (smaller in size than sand), and concrete may contain anything from sand, to gravel, to rebar.
Sometimes there is a confusion about the differences between something that is hard and something that is brittle. Something may be hard not be brittle, such as steel. Hit steel with a hammer and nothing happens. Something may be hard but also be brittle, such a diamond. Hit a diamond with a hammer and the diamond shatters. Bricks and cinder blocks are brittle.
I don’t know of anything to use to weaken a cinder block except for maybe drying it. However, blocks are dried at the time they are made so there is very little moisture in them. The drying of a block relies more on the drying time than on the drying temperature. To dry a block, use a relatively low heat oven, maybe 130 degrees, and cook the block for hours or even days. Any gain in ease of breaking is probably more in the mind of the breaker than it is based in fact. If the breaker thinks the block will be easier to break, it will be.