There is no specific “up” or “down” direction that block have to be laid in. You may hear a masonry say that block are manufactured “upside-down”. This means that the block molds are slightly wider on the bottom than the top. The reason is common sense – so you can lift the mold off of the freshly compacted block. The mason will usually turn the block over before he picks it up so he is holding the thicker portion of the web. It is simply easier to grip and hold the thicker end. Structurally, it makes no difference.
Jerry Painter, FASTM
Don Beers, PE, GC
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