6. Wood not anchored into earthen floor well enough
We have split level floors, and so there's steps and short 'walls' between levels which are topped with madrone wood. Underneath this plaster, there's stone walls holding in the upper level - like a terrace. Stupidly, when I was putting on these wooden pieces, I didn't want to use some fancy chemical glue to fasten the wood down to the stone. (I'm too 'all natural' for that! I thought to myself) and so I used mud and had nails and screws going into the back sides of the wood. Well, of course they get traffic, and they move a bit. Thus, the floor behind them doesn't flex as much as they do, creating cracks. Advice: don't have edges on your floor. if you do, use good glue to hold them down.