Hi,
I used 4 x 4s set in concrete to build a level 8’ x 8’ frame for a hot tub pad that is 5-6 inches deep (depending on the location within the frame), and the frame is set atop a newly laid but slightly skewed shed floor made of 4 inches of rammed dense-grade gravel that is covered by a thin layer of Portland cement, all watered down (the shed floor was my landlord's idea and his work, not mine). I also still have a pile of dense-grade gravel in my driveway that I'd like to use to build the pad. (I know concrete for the pad is the best option, but I'm on a tight budget.) The hot tub weighs 3,090 pounds when filled, and it will be arriving sometime this month.
Now I could do the following 3 things with the dense grade to form the pad, and I’m wondering which you think would be the soundest option:
1. Completely fill and tamp dense grade in the frame and have that serve as my hot tub pad.
2. Do the same procedure in option 1, except water the dense grade thoroughly after all the dense grade is tamped.
3. Tamp and water a layer of dense grade three times (for a total of 3 layers), but not starting a new layer until the previous layer hardened.
Option 1 concerns me because I'm not sure the dry pad—which of course would contain fairly large rocks (and thus countless air pockets)—wouldn't eventually sink somewhere, causing the tub to tilt.
Options 2 and 3 appeal most to me because of the hardening effect that water has on dense grade, potentially offsetting structural concerns due to an unhardened pad and air pockets. But these options are also the ones that could cause me to lose the most sleep at night: The reason I’m concerned about Option 2 is I suspect that no matter how long I water the pad, the water will penetrate only the upper 1 to 2 inches of dense grade, resulting in a pad with two structurally distinct layers, with the top one being firm but thin and the bottom one dry and relatively loose, which I suspect may lead to problems. Option 3 concerns me because I suspect I will have 3 hardened yet thin and “disconnected” members of the pad, which could lead to problems as well. That is, it seems to me that each of the three layers would not be structurally bound to the other 2 layers.
Please help. I'm struggling over here.
Addition to original post:I thought of 2 more options:
4: I could make “super dense” dense-grade gravel by sifting the larger rocks out of it and then building the pad with it. No water, like in Option 1.
5: I could use “super dense” to make three layers, watering each one as I went, like the procedure described in Option 3.
Follow up:
Never mind. I went with concrete.
