Hot tubs are a popular addition to any home, especially for people who entertain regularly. Most people put hot tubs outside. They weigh around 4,000 lbs. fully loaded, so it's important that the structure you place the hot tub on can handle heavy loads. Grass or bare dirt just won't do. If you choose to place your hot tub on a concrete slab, you''ll have to build something more substantial than a normal 4-inch concrete pad, due to the weight. You'll need footings much like the foundation of a house.
Stake out the perimeter of the slab you want to pour. Slabs for hot tubs generally are 8 feet by 8 feet. Run twine between the stakes.
Excavate the concrete pad area 6 inches deep. Excavate the perimeter 1 foot deep and 1 foot wide to form a deeper trench around the excavated area.
Build the forms for the footings by placing the 2-by-10 lumber around the outside of the trench and securing them with wooden stakes. Secure the 2-by-6 lumber on the inside of the 2-by-10 lumber, 6 inches away, forming a 6-inch wide frame for the footings you're about to pour.
Dump 2 inches of gravel into the trench inside the forms you just built.
Mix the concrete using your wheelbarrow, hose and shovel according the manufacturer's directions.
Pour the concrete into the forms to create the 10-inch-deep footings that will support the weight of the pad and the hot tub. Flatten the top surface of the footing by running a 2-by-4 along the top edge of the forms.
Wait two days before removing the wooden forms from the footings. They will cure fully in about a month, but you don't have to wait for that before moving on to the next steps.
Tamp down the dirt inside the footings, which should be about 6 inches below the level of the footing you just built. Pour an even, 2-inch layer of gravel onto the tamped dirt, then tamp the gravel down as well.
Mix more concrete as before, then pour it into the enclosed footing, using the footing as your form. Run the 2-by-4 along the top surface of the footing to make the central pad level with the footing.
Allow to dry and cure for 20 days before placing the weight of the filled hot tub onto the pad.