Concrete Slab + Large Fish Tank = Worried, will it be okay?

[iReefer12]

I’m pretty far along with the build of a 700 gallon tank, and someone mentioned to me

“Hey, you should be careful, if you have a monolithic foundation, you’ll need to have the void filled in beneath in order to support all that weight”

Call me naive, I just figured that, concrete slab = totally safe..

I’ve researched monolithic foundation, and I don’t think I have this style of foundation, I think it’s a floating slab…

Here are some pictures:

The tank is 10’x45”, so 40sqft. Roughly 250lbs per sqft (I’m factoring weight of the stand, sump weight and Frag tank).

So my worry is, will my concrete slab floor be able to hold the weight of my tank… or should I be worried?

 

[Stealthreefer]

It's on the wall?
The slab is thicker at the walls and thins out in the middle. If tank is on the wall then that's the strongest place, if floating in the middle of the room you should maybe ask your contractor/concrete guy.

 

[iReefer12]

It’s in the center of the room….

 

[Stealthreefer]

I don't think there is a void it's just thinner a few feet from the wall. It's supposed to spread out force more evenly since it's all 1 pour so probably okay. That seam (6108) is kind of worrying me.

No cracking in the foundation or anything right?

 

[iReefer12]

The control join towards the end of the tank?

 

[Thumbster]

What void is this person taking about?

Your walls are setting on footers. The footer is the wider concrete under your walls. They’re poured wider so there’s some wiggle room to get the wall’s square when they’re setting the forms for the walls. The footer also sets on undisturbed (settled) ground so the walls don’t sink. Although they will still settle some.

Your floor (from what I can tell) was poured directly onto the dirt or maybe pea gravel if they had to fill any voids.

Your floor should also be the same thickness in the middle as it is against the wall.

Edit: a monolithic foundation is poured directly onto the ground and has no voids anywhere either.

 

[iReefer12]

Yeah, I’m not an expert in the matter, I just figured, it’s a concrete floor, and there’s dirt below it, so if I couldn’t put it on that, then what structure would I put it on haha

Okay, so you think I should be okay?

 

[2Flash1]

4” or 6” thick? You’ll be fine nonetheless. Just remember it should have rebar and construction people drive gradalls on concrete slabs 4+”.

*Gradalls weight 30000 plus lbs!

 

[YOYOYOReefer]

That’s only like 1.7 lbs per square inch. Ya your floor will not have any issues at all

 

[iReefer12]

No, don’t see any cracking anywhere.

I wasn’t there to see the pour, so I don’t know if they put rebar in, I assume they did.

 

[Thumbster]

Yeah, I’m not an expert in the matter, I just figured, it’s a concrete floor, and there’s dirt below it, so if I couldn’t put it on that, then what structure would I put it on haha

Okay, so you think I should be okay?

I wouldn’t be any more concerned about putting your tank there than I would be if it was setting on your driveway.

 

[KrisReef]

Do the stand feet act like high heels in this scenario or is the stand flat on the floor?

Great original question btw!

 

[iReefer12]

They are 1” steel feet. They are rated for 750kg each. And there are 15 of them.

So, it works out to about 633lbs per (foot) so 633 lbs per sq-inch. Albeit, I would think that the load gets distributed evenly through the concrete slab, so would then distribute over the full surface area of the tank.

- this is all just in theory, so I hope my thinking on all this is correct.

P.S. I like the driveway analogy. That gives me some piece of mind thinking of it like that.

 

[BeanAnimal]

It's on the wall?
The slab is thicker at the walls and thins out in the middle. If tank is on the wall then that's the strongest place, if floating in the middle of the room you should maybe ask your contractor/concrete guy.

Why would the slab be thicker near the walls? A basement o foundation slab would typically be uniform thickness. It may or may not have integrated footers, depending on frost depth.

 

[BeanAnimal]

No, don’t see any cracking anywhere.

I wasn’t there to see the pour, so I don’t know if they put rebar in, I assume they did.

An on grade basement slab would not typically be reinforced with anything more than wire mesh.

 

[iReefer12]

They used the wire mesh on the driveway, I did see that.

With no Rebar, does that cause some concern for weight bearing ability? (There’s got to be a better way of saying that)

 

[Thumbster]

Rebar will make the slab stronger because it distributes the weight from one point to the rest of the slab but I don’t think it will make any difference in your situation since it is setting on the ground. The weight goes straight down to the ground rather than flexing the concrete around it. If that makes sense.

The concrete in your floor is probably 3000psi minimum depending on the mix and how much, if any, water they added to make it easier to work. Your floor looks good from what I can see in your pics so I wouldn’t be concerned with weak concrete.

If I was concerned about anything it would be the 600+ pounds resting on the 1” foot. That seems like a lot of weight but if it’s rated for that I guess it’s okay. Do they make a bigger foot?

 

[Stealthreefer]

Why would the slab be thicker near the walls? A basement o foundation slab would typically be uniform thickness. It may or may not have integrated footers, depending on frost depth.

It's supposed to be thicker under the walls on a mono pour.
Everything I have ever read or been told and the google pictures I am now looking at because you made me second guess also confirm that.

 

[iReefer12]

They do make a bigger foot.

The current foot is rated for 750kg, so 1600lbs.

So 15 x 1600 puts the load bearing capacity at 24,000lbs… am I thinking about this the right way? Or overlooking something?

Or are you more concerned about the weight being applied to the concrete in such small points?

 

[Thumbster]

They do make a bigger foot.

The current foot is rated for 750kg, so 1600lbs.

So 15 x 1600 puts the load bearing capacity at 24,000lbs… am I thinking about this the right way? Or overlooking something?

Or are you more concerned about the weight being applied to the concrete in such small points?

Ok the foot seems like it should be plenty then. It probably won’t be a problem on the concrete either but if they make a wider foot or if you can put a small plate or pad of some sort under your existing foot to spread the load on the concrete it wouldn’t hurt.

Also I say this without knowing what your feet look like so I may be overthinking this.