I am pouring a 5 inch concrete pad for a hot tub. I am planning on putting down 4 inches of compacted gravel under the concrete with rebar mesh in the center. My concrete pad will be 9 feet by 9 feet. Should I clear an area a few inches larger than 9 feet and compact the stone and place the form on top of that for my concrete (5 inch tall form) or should I use a 9 inch tall form and compact the stone inside the form and pour the concrete on top? I have seen a few videos of it done both ways and I was wondering which was better. Thanks.
The problem with just pouring a flat slab is the rock can migrate out if above grade. If this pad base will be at grade or below so the rock can not migrate it will be fine to leave it flat. If you are adding the rock on top of grade make it a monolith pour so the outside edge goes down to grade this also creates the footing I usually add.
If I think a Gazebo or a roof may be added I will create a small footing trench (an additional 4x4” deep/wide ) so the pad edge could support a small structure on the perimeter.
As a patio you are going well beyond what would be needed at 5” thick reenforced but I would still add a thicker perimeter edge just in case.
You don’t have to make the pad wider to do this just don’t fill the gravel all the way to the form to make the footing.