As a forewarning it's immensely important to either backup

 It forces you to use strong Minecraft Mods blocks and stable construction for your structures to stay together.

 Your save or start a new one before loading this mod.

 You might finish up destroying many of your preferred structures otherwise.
Blocks will stack normally but a good most them aren't strong enough to hold up in mid air.

 As soon as they are put by you on the side of a block with no support below, they'll fall season to the bottom.
If you use more robust blocks like bricks or planks however, Stop Physics is a wondering little mod with major implications. blocks with more structure, you'll be able to place them privately of other less secure blocks.
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