How Flat Does A Base Need To Be?

[stevenw00d]

I am taking delivery of a used Sundance Optima hot tub on Wednesday. I've been working on the base, and although it is pretty dang flat, it isn't perfect. I'm a mechanical designer, so by nature this has me wondering... how flat does the base have to be? I am using Ez Pads under the hot tub and have between 2" and 6" of crush and run (aggregate) and 1/2" to 1" of sand on top of that. The Ez Pads are definitely within 1/4" of flat all over, but depending on where I'm checking and how, I am getting some small gaps under a 6' level. I would certainly assume this is level enough, but how the heck would I know? I've searched everywhere and no one seems to give a tolerance.

I greatly appreciate your replies, and hopefully this will be a helpful to others in the future as well. (surely more people have wondered about this???)

[Spa_Guru]

Any deviation from flat is going to equal stress on the framework of the spa, so if your pad sags, the spa will flex to match it.

The more it sags, the worse the cover fits, and the more it costs to heat.

I would ask my dealer, and GET IT IN WRITING what the tolerance is.