Thin concrete floor, Pour pad?

Coasterfrk

New member
Looking to do a large 250-300g tank in our basement. I know that the floor is very thin somewhere around 1-3 inches. Digging out and pouring deeper isn't easily doable. Could I pour a concrete pad on top of the existing floor to place the stand on?
 

sirreal63

Go Spurs Go!!!
Premium Member
Pouring on top will not make a proper footer. To do it correctly you must dig and pour properly. If it is 3" I may not be concerned, if it is less I would be concerned depending on the soil underneath the slab. If using a metal stand I would be even more concerned about point loading the slab if it is under sized.
 

Coasterfrk

New member
I'm planning for it to be wood... Just because I don't know why how is a block of concrete above ground pushing down different from a block of concrete in the ground pushing down. And for that matter wouldn't it still add strength to the floor?
 

davidfrances

New member
I have both my 250G tanks sitting side by side on my concrete floor in my basement, but I am certain the concrete is thicker than 1".

I don't know much about concrete, but do know that if your floor is only 1" thick, it would rapidly crack and buckle just from seasonal variations.

How old is your house? Is there a way that you can drill a test hole and measure the thickness?
 

sirreal63

Go Spurs Go!!!
Premium Member
It would add strength directly under, but not to the adjoining section of slab around your pour and this is where it would crack as it is now the weakest section.
 

Coasterfrk

New member
I was able to confirm through a piece I did break up. It's definitely 1" in some spots closer to 2" in others. The house is about 120 years old.
 

Coasterfrk

New member
The concrete that would be in front of and next to the tank is already covered with finished flooring. Would it be good to just break out where the tank sits dig deeper and pour a pad?
 

Kenmx10

New member
I would cut out the area of concrete a little larger than the tank. If your tank is 6x2, cut out a section about 8x4. You can get a diamond blade that will fit a standard circular saw for about $20 to cut the concrete.
Dig down about 12" and install a couple pieces of rebar that you can get from Home depot for about $20. Back fill with concrete and it will be more than enough to support your tank. Should be able to do this for less than $100. Not including replacing any hardwood flooring.
 

Jreed983

New member
I would cut out the area of concrete a little larger than the tank. If your tank is 6x2, cut out a section about 8x4. You can get a diamond blade that will fit a standard circular saw for about $20 to cut the concrete.
Dig down about 12" and install a couple pieces of rebar that you can get from Home depot for about $20. Back fill with concrete and it will be more than enough to support your tank. Should be able to do this for less than $100. Not including replacing any hardwood flooring.

+1
This would definitely be the way to go but the $100 estimate might be bit low. If you were to do this and buy 80# bags of concrete mix it would take approximately 55 bags which alone would be around $175. You might be able to get it cheaper if you did a ready-mix/u-cart from a rental store around you.

If you go this way, if your slab is thick enough you should drill in to the cut sides of the existing slab and insert rebar pieces. Then tie them into the rebar structure you build in the new section.
 

ryansc

New member
it looks like you need to dig out and re-pour. you mention that it is in a finished area, but that the floor is only 1"-2" deep from your test dig.

now just imagine. You don't go through with the re-pour. Get the tank set up leveled and filled. then 6 months down the road the floor starts to give under the weight of the new tank. Tearing down your newly established tank to reinforce the floor properly then re-set the tank seems like a much bigger headache than if you just did it correctly the first time.

To the actual pouring. I would add that you probably want to add packed layers of rock, crushed rock then do the cement layer. I used to build houses and when building the foundation we never poured one without the proper sub levels of rock and crushed rocks under the cement pads. you can rent a small earth compacter or get one of those heavy steel rods welded onto a plate and manually pack it. With such a small area i am not sure i would rent the compacting machine. I have just never done it without one.

And then if you really want to make sure it doesn't crack you can pour compacted concrete. If you don't feel comfortable doing this yourself hire a contractor in your area or watch youtube to become familiar.

In any case. If i was putting up a large tank that i was investing 10's of thousands on dollars in. I would take the time to make sure the floor and sub floor could support it. I mean, your talking a few hundred in materials if you do it yourself and one weekends time vs not and then taking everything down setting up temp tanks to hold whatever livestock and corals you have and keeping them alive and happy for about a month while the new concrete sub floor properly cures and dries.

best of luck
Jiambi
 

Kenmx10

New member
+1
This would definitely be the way to go but the $100 estimate might be bit low. If you were to do this and buy 80# bags of concrete mix it would take approximately 55 bags which alone would be around $175. You might be able to get it cheaper if you did a ready-mix/u-cart from a rental store around you.

If you go this way, if your slab is thick enough you should drill in to the cut sides of the existing slab and insert rebar pieces. Then tie them into the rebar structure you build in the new section.

I count 28 bags.http://www.quikrete.com/Calculator/Main.asp
 

Jreed983

New member

Your right it does say that but that is only for a 4" thick slab so that would need to be tripled for a 12" slab.

I definitely agree with putting a good layer of crushed rock under the slab. You would also probably be plenty safe with 6-8" thickness for the concrete. This has always been the standard I've seen for foundation footers and they hold up an entire house.
 

CStrickland

New member
It might depend where you live, too. Anyplace where the ground freezes I would deff chip the old floor out and dig down. Think of the house as a rigid square floating on a shifting mound of dirt. The more the mound moves, the more the square cracks. It's not so much that it would sink into the ground, as it would come out of level, or bow the stand such that the frame cracks (worst case scenario, obvs).
 

Kenmx10

New member
Your right it does say that but that is only for a 4" thick slab so that would need to be tripled for a 12" slab.

I definitely agree with putting a good layer of crushed rock under the slab. You would also probably be plenty safe with 6-8" thickness for the concrete. This has always been the standard I've seen for foundation footers and they hold up an entire house.

Recheck the math. 8'x2'=16'sqf. The number of 80b bags for 6" equals 14. Multiply by 2 for 12" gives you 28 bags.
 

green_troll

New member
Dont know if its been said but id tie the new slab into the old one.
which could be tricky if the old slab is that thin....
But that way it acts as one slab again and you wont have movement between them.
 

Jreed983

New member
Recheck the math. 8'x2'=16'sqf. The number of 80b bags for 6" equals 14. Multiply by 2 for 12" gives you 28 bags.

Your right that math is acurate, however the size pad you originally suggested and I agree with was an 8'x4' which equals 32 sq.ft.. This would be double your math here which would equal 56 bags.

Aside from this, OP, I would go with these same dimensions but with a 8" thickness rebared to the surrounding slab (if thickness permits) and a approx. 4" thick rock substrate. I've dealt with this exact scenario before when installing industrial machines in factories with inadequate floors for the machine size and did it just like this. Pm me if you need any more detailed ideas.
 
Top