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Going completely level/zero slope is fine for the footprint of the tub. Just have the four surrounding sides slope away gently.
I don't mean to hi jack the OP's thread, but I'm looking for guidance on a similar issueI have an 8 ft by 16 ft stamped concrete patio on which I'd like to drop a hot tub. However, my village wouldn't allow the concrete workers to leave a zero slope where the hot tub would ultimately sit. So I now have a 3" fall across the 8 ft width (from house to edge of concrete patio). This is obviously done to protect the house, but has now created quite a challenge for a level base for the tub.I'm trying to keep the patio clean, and prefer not to use sand or pea gravel. This would be our first tub, and if I don't like it I'll dump it and don't want the mess. Can anyone suggest solutions here? A smart neighbor recommended someone laser-cut a large piece of fiberglass for under the tub.No hot tub installer in my area is willing to touch this situation, probably cuz they don't want the hot tub install warranty exposure.