Building A Level Hot Tub Pad

[jacobbencke]

I'm looking to buy a larger size hot tub (Hot Spring Grandee, Sundance Maxxus) and need to provide a level surface to install it. I already have a concrete patio that is in good shape, but it has about 2" slope over 8' in one direction which appears to be more than the recommended. These spas are too big to shim, so I need to build a level pad on top of my patio. It seems like I have 3 options:

1) Wood deck. However that requires maintenance.

2) Concrete. Building a wooden frame and filling with concrete. The concrete pad is obviously the most stable and long lasting, but I would like it to be removable if I ever get rid of the tub. One contractor said he could coat the patio with oil so the pad didn't really stick, it would just kind of sit on top of the patio. The outer wood frame would be bolted to hold everything in place. How thick at pad would I need, at the thinest part?

3) Gravel. Building a wooden frame and filling with gravel. Is this approach OK for larger tubs or only smaller one. How thick a layer would I need at the thinest part?

I woud appreciate any feedback.

[yellowdog]

I did a little research because I have no good answer for you. My tub went on a cement patio. Type in google search "how deep must the gravel be for a hot tub" You will find tons of answers that will help with your decision. By the way two nice tubs you are looking at. I have the Sundance Optima and love it. Good luck.

[Spa_Guru]

I have the perfect solution, I have done this many times.

1) Put down some 5 mil plastic.

2) Calculate the exact slope, and cut strips to build a form exactly the size of the bottom of your spa. Check to be certain it is level.

3) Using mortar mix, not concrete mix, pour yourself the wedge pad you need and scrape it with a board to make it even.

4) Place the spa on the form, and cut off the excess plastic.

If you ever move the spa, the plastic keeps the mortar wedge from sticking to the existing patio, it comes right up.

[jacobbencke]

good idea. does the plastic go under the form, or line the inside of the form? Since you've done this before, did you screw the form down? I'm assuming pressure treated wood. Did you paint it, if so any specific paint? And lastly, how thick should the pad be? I'd prefer to keep it as thin as possible so the spa height doesn't get too high. thanks

[Spa_Guru]

I put the plastic under everything.

I do not screw the form down, I just screw the pieces to each other.

Make it as thin as you like. The last one I did was only a three sided form, two seven foot wedges tapering from 1" to nothing connected by a one inch cross piece.

I do use pressure treated wood.

[Spa_Guru]

Don't be afraid to make the moartar mix a little runny, it makes the job easier.

Remember, no concrete mix, it has pebbles in it.

[jacobbencke]

the dealer emailed me and recommended concrete pad that could support 120 lbs/sqft. If I make it 1" thick at one end and 2" at the other will that meet that need? I'm looking at a big 500+ gal tub, so I want to make sure I build something strong enough to support it.

Most of the research I've found addresses pouring a brand new pad and always specifies 4" thick. Since I already have a solid patio underneath it's different story. Do I need to worry about a thin pad cracking? Do I need any rebar?

[Spa_Guru]

The concrete I am talking about pouring is going on top of concrete, so it doesn't need to be independently structural.

No reinforcing is required, just what I described.

The last one I did (Yesterday) was nearly 3" at one end tapering to nothing over 90"