# How do I pour an in-ground concrete tub?



## tibberous (Mar 25, 2010)

I am just about finished digging a 4 x 6 x 3 foot hole (HARD AS ****)

I want to pour concrete sides and a floor, then paint it with a 5 gallon thing of swimming-pool type paint.

It will never freeze.

I'm thinking I might be able to get away with pouring it 4" thick without rebar, and relying on the clay soil and concrete to hold in the pressure of the water - but I'm not sure. I also don't really know how to pour it -- I was thinking:

- Pour a 2-3 in bottom just to create a solid, level surface for the forms.
- Build wall forms out of plywood and 2x4 (the inside would be plywood, the outside would be dirt)
- After the walls cured and the forms were removed (how do you get the plywood off the concrete?), pour a deeper floor, for better waterproofing.

Does this sound at all right? On one hand, I can't see it cracking, just because the clay soil is so damn hard -- I just want to make sure I do it right though, figure it will be holding almost 3,200 pounds of water!


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## Canarywood1 (May 5, 2012)

tibberous said:


> I am just about finished digging a 4 x 6 x 3 foot hole (HARD AS ****)
> 
> I want to pour concrete sides and a floor, then paint it with a 5 gallon thing of swimming-pool type paint.
> 
> ...


 
Not a good idea,your better off getting one of the plastic jobs from HD or Lowes,they come in different sizes.


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## tibberous (Mar 25, 2010)

Canarywood1 said:


> Not a good idea,your better off getting one of the plastic jobs from HD or Lowes,they come in different sizes.


I'd have to take out a wall and a floor to get it down stairs.


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## jomama45 (Nov 13, 2008)

What are your plans for keeping the water from constantly leaking out of it, or dirty ground water from leaking in if it's empty???

Contrary to popular belief, concrete is far from waterproof........


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## joecaption (Nov 30, 2011)

You spent all that time digging the hole before doing the research to see if it would even work

Clay one of the worst soils to have under a slab or any concrete. It shrinks and swells.

How do you plan on getting the water in and out of this?


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## tibberous (Mar 25, 2010)

joecaption said:


> You spent all that time digging the hole before doing the research to see if it would even work
> 
> Clay one of the worst soils to have under a slab or any concrete. It shrinks and swells.
> 
> How do you plan on getting the water in and out of this?


Water line and a sump pump. There was already a polyethylene tank there (above ground), but it was only 100 gallons (biggest one that would fit thought the door)

This new one is HUGE! I tried to make it bigger than needed, just because it won't be practical to expand it later.

Should I lay a bed of gravel before I pour the floor? I've seen that done, but never really knew why.

Keep in mind, this is inside and below the frost line.


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## cleveman (Dec 17, 2011)

This is a great project. I love it. Just let all the criticism roll off you. Those other guys are just jealous.

First thing, I think you need to dig some more. What size do you want the basin to be in the end? You mentioned a 6x4x3 hole. Does that mean 3' deep? Or will you be coming up off the surface with the basin?

I would just plan on some overdig of 4" on the sides. Dig down 4" deeper than you want to be. Then put in some 2x4 forms for some 16" wide footings. Then dig down in the formed up 16" wide area another 4". Put 2 lengths of 1/2" rebar in this 8" thick footing all the way around. Have rebar sticking up vertically from the footing where the cores of your concrete block will be. Fill the footing with concrete, then strip the forms.

Now you have your footings 4" above the grade with re-bar in them and sticking up out of them. Next put in 4" of rock, so it is level with the top of the footings. This will give you a nice, clean, smooth area to work in. Your footings are 16" wide. In the center of the footing, lay 8" concrete block all around your basin, up to the height you want, minus 4". We'll cap this with 4" cap blocks later.

When you are done laying the block, fill the block cores with concrete. You'll have rebar in these cores as well. Just put a rebar in every core, why not?

Now pour 4" of concrete on the floor. This will rest on the footing edge and against the concrete block.

Next you'll want to waterproof the basin and up over the cap blocks as well, and backfill the 4" overdig with more rock.

You can now fill it with water and do whatever you had planned on doing next.


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## tibberous (Mar 25, 2010)

cleveman said:


> This is a great project. I love it. Just let all the criticism roll off you. Those other guys are just jealous.
> 
> First thing, I think you need to dig some more. What size do you want the basin to be in the end? You mentioned a 6x4x3 hole. Does that mean 3' deep? Or will you be coming up off the surface with the basin?
> 
> ...


Funny you mentioned using concrete block, I had originally thought about this but thought the mortar joints would create more problems than simply using forms.

Not sure why my idea is getting any criticism thb, I believe basement foundations are poured in a similar fashion, and those are a magnitude larger and have to deal with the elements.


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## user1007 (Sep 23, 2009)

Hate to step in and quash enthusiasm but you have not disclosed the lay of the land to us. Are you on flat land or is this concrete pit you plan to build subject to whatever forces the ever so slight slope you plunk it in might put on it. And you expect the walls on that side of lateral forces to hold for how long without reinforcement?

And you are planning to add the weight of how much water? Water is one of the most wonderful but dangerous substances on the planet. A major part of all of us is water. It, more than just about any substance I can think of adapts to live load changes almost instantly but can trasmit and transfer them in the next heartbeat. The thought of you thinking you can contain those loads without reinforced walls is just plain scary. Even on calm days water just wants to respond to gravity. Anywhere in the World, if it could, it would go home and get back to sea level or below.

I used to design features like you have in mind in to landscape designs all the time. Then I handed my drawings over to pool designers with engineering staff to make them work---safely. Would your ego be totally done in if you admitted you were in over your head (pun intended) on this and sought out a local pool, spa, whatever designer to help you with this? Your idea sounds like it could turn out to be spectacular. I know we guys don't like asking for help but if you find the right pool/spa guys you will end up with what you really want and for a lot less money than fixing this approach you have in mind when it is floated south on whatever you put in this tub concept.


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## SeniorSitizen (Sep 10, 2012)

I have a 1909 Kohler cast iron tub you can have to bury and the hole you've dug is about right. Bring pizza :thumbup: and at least 4 strong helpers to load. It takes 2 just to turn it over.


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## Canarywood1 (May 5, 2012)

"I know we guys don't like asking for help but if you find the right pool/spa guys you will end up with what you really want and for a lot less money than fixing this approach you have in mind when it is floated south on whatever you put in this tub concept."


If you really want to do this project,i'd take sdsester's advice and contact some pool/spa builders,for it to hold water it should be a monolithic pour,not a two part pour,better yet gunnite would insure it being water tight.


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## pwgsx (Jul 30, 2011)

I wana see pics of the hole


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## Jackofall1 (Dec 5, 2010)

Sounds like this is either in the basement of a house or in the crawlspace?

I want to see pictures to.

Building a water tight concrete tub into the ground has me asking a simple question..........how high is the water table in your area. I am not talking about now, I guess its dry as you are digging a hole in it, but will it rise?

If it does rise your tub will turn into a boat and start floating.

As for building a water proof tub, I am sure you can find some direction fairly easily by searching the subject.

http://www.ehow.com/how_4690387_build-concrete-hot-tubs.html

http://www.youtube.com/watch?v=otp10UhiBUE


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## pwgsx (Jul 30, 2011)

Very interested to see this, post some pics ASAP


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## tibberous (Mar 25, 2010)

pwgsx said:


> Very interested to see this, post some pics ASAP


I will once I'm finished digging.

Question though - what about skipping the concreting completely and just getting a pound / swimming pool liner? Or concreting, then using a pound liner, since your have a way to glue it.


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## pwgsx (Jul 30, 2011)

Before you dig anymore, PLEASE post some pics. A pool liner for a bathtub....dude :laughing:


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## user1007 (Sep 23, 2009)

I forgot to ask how you plan to fill and drain this thing and what systems you have in mind for treating and heating the water to hot tub temp? The ground around it will suck ambient temperature instantly. 

You could do a natural design or one conventional with a filter and all that jazz. Natural pools, tubs and spas are becoming the rage and they should. They are beautiful and complete sustainable environments. Low or no chemical requirements. Kids get to play with some aquatic creatures. 

Unless you are into weird toe fungus and raising mosquitoes you cannot just leave a tub of water outside.


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## user1007 (Sep 23, 2009)

pwgsx said:


> Before you dig anymore, PLEASE post some pics. A pool liner for a bathtub....dude :laughing:


It stopped being just a bathtub when he decided to bury it in the ground. Why is this funny to you? He has to line it with gunite, vinyl or something does he not? :yes:

I say again, call a pool or spa designer in on this.


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## pwgsx (Jul 30, 2011)

sdsester said:


> It stopped being just a bathtub when he decided to bury it in the ground. Why is this funny to you? He has to line it with gunite, vinyl or something does he not? :yes:
> 
> I say again, call a pool or spa designer in on this.


 
He is talking about a TUB in his house, dug in the ground ( assuming its in the basement) and wants to line it with a pool liner. Now to see the look on a pool/ spa designers face when he comes out to see this big hole dug in this guys basement...... Non of this yet is funny to you?? :wink:


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## user1007 (Sep 23, 2009)

pwgsx said:


> He is talking about a TUB in his house, dug in the ground ( assuming its in the basement) and wants to line it with a pool liner. Now to see the look on a pool/ spa designers face when he comes out to see this big hole dug in this guys basement...... Non of this yet is funny to you?? :wink:


Explained as you did, it is hilarious. :laughing::laughing:

Somehow I missed this was a hole in his basement. I would still be calling a pool and spa company though. :yes:


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## pwgsx (Jul 30, 2011)

Im assuming basement- he said up top he couldnt fit a pre-made tub down the stairs.


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## user1007 (Sep 23, 2009)

tibberous said:


> I will once I'm finished digging.
> 
> Question though - what about skipping the concreting completely and just getting a pound / swimming pool liner? Or concreting, then using a pound liner, since your have a way to glue it.


I am done. You want affirmation your half baked approach to this will somehow work. 

I say, for the last time, this is not a DIY project. Call in a pool, spa or tub designer that build to the approved specs they provide if you want to do the work yourself. :furious::furious:


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## cleveman (Dec 17, 2011)

Tubs-r-us,

Have you got that hole dug yet?

Don't worry about what everyone is saying. 

Worst case scenario, you can put a slatted floor on it and raise some hogs on top of it.

Give us a progress report.

Regarding waterproofing, I want you to plaster it nice and smooth with some fiber reinforced plaster, then hydro-ban the bejesus out of it.


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## shinyhalo (Oct 6, 2011)

Don't let the negatives on these forums get you down! 
OMG
I encountered the same thing on my post about a warped wooden base flooring fix. I went ahead with my idea and it turned out GREAT.


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## pwgsx (Jul 30, 2011)

Where are the pics :clap:


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## Pianolady (Jun 28, 2012)

I don't think OP ever said exactly what his plans for this are. Will it be an indoor pond?


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