# concrete thickness for patio hot tub



## denemante (Apr 2, 2010)

Hey all - we have an existing poured cement patio the previous owner put in a few years ago. It's about 30 feet wide by about 12 feet out. I believe it's 4 inches thick. It butts up to the house on one side, lawn on the other, and on either end, it butts into cement retaining walls. On one of them, there are actually stacked 8x8s that further retain a bit of the earth out towards the lawn.

I want to put a hot tub on this patio at the end with the 8x8s.

However, I had some septic issues a few years ago. I didn't trust the guys who came out. But nonetheless, they noted where the main house drain flows into the tank. I saw it with my own eyes as well. Instead of flowing into the tank on a downhill angle, it was almost level if not slightly uphill. This is just what appeared to be a 6 inch PVC pipe.

It comes straight from the house (underground, then makes a 90 degree turn into the tank.

These guys thought that perhaps when the patio was put in, it pushed down the whole main drain pipe, causing the 90 degree turn to push down, and the little 2 foot final run into the tank is now almost level or pointing slightly uphill. There are zero cracks in my patio nor gaps where they meet the walls.

They said to fix it, I'd have to jackhammer my patio to readjust that main drain line. But I haven't had any septic problems since, however. I had my yard graded better and the problem was solved.

But now I want to put a hot-tub here. Is that going to sink the whole patio and increase the potential issue they noted with the pipe grade? Or would a patio this size easily handle a hot tub?


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## Canarywood1 (May 5, 2012)

That patio being on top of the pipe, is 18,000 lbs. so i'd guess it would have some effect on the drain line, and the additional weight of the hot tub may not help matters, being that water weighs 8.3 lbs. per gallon.


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## ront02769 (Nov 28, 2008)

Could be right with respect to impact on the pipe...but hot tubs are decently heavy. Mine is 700 lbs empty, add in 300 for a couple of decent size adults making it. 1000. Then 410 times 8.whatever coming in at about 4500 lbs. ron


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## Msradell (Sep 1, 2011)

Canary, I didn't bother calculating the weight of the concrete but assuming your calculation is correct that equates to only 0.34 psi which is nothing! As for the hot tub, if you use a size of 8'x8' and the weight of 4500 pounds it only adds another 0.48 psi which again is very minimal. Combining these two is still significantly less than the pressure put on the ground by one person standing on it.


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## TRUEPRO (Apr 10, 2012)

Id pour 5" thick with fiber and wire. Stronger the better, right? And the extra 1" and fiber is only 8% overall increase in material cost.


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## AMHope (Oct 28, 2014)

I do not believe the extra 4500 lbs is going to have any effect at all- and if you are asking if you need to re pour the entire slab due to the hot tub being added then I would say absolutely not. The fact is dirt will only compress so much. While the whole concrete slab does certainly add a lot of weight- adding a relatively small 4500 MORE lbs is pretty insignificant. 

As long as the hot tub is not going to be sitting directly over the sewer drain line I would not expect and issue. Also, If you place the hot tub on any type of build base that increases the footprint and further distributes the weight.


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