# weight of a concrete floor



## overlooker (Mar 7, 2011)

I would like to pour a concrete floor in my second-floor bathroom. It's a small bathroom, but I want to be sure I won't be adding too much weight to the floor by doing this, and compromising the structural integrity of my house. I'm planning on a thickness of about 1/4-1/2 inch. Anyone have any information on this? The internet has not been very useful so far on this question.


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## joecaption (Nov 30, 2011)

Why in the word would you want a hard, cold, poris floor in a bathroom?
Anything that thin will just crack.


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## Canarywood1 (May 5, 2012)

overlooker said:


> I would like to pour a concrete floor in my second-floor bathroom. It's a small bathroom, but I want to be sure I won't be adding too much weight to the floor by doing this, and compromising the structural integrity of my house. I'm planning on a thickness of about 1/4-1/2 inch. Anyone have any information on this? The internet has not been very useful so far on this question.


 
Exactly what kind of info do you want?


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## Daniel Holzman (Mar 10, 2009)

Concrete weighs approximately 150 pounds per cubic foot. That means that every inch of concrete exerts approximately 12.5 pounds per square foot of load on your floor. Whether or not your floor can support the load of concrete requires knowledge of the bearing capacity of your floor, which you can compute if you know the size of the joists, the span, the spacing, and the species of wood. If you do not know this information, and do not know how to use it even if you have it, most recently built bathrooms are designed to carry a total load of approximately 30 pounds per square foot.


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## Mort (Nov 26, 2008)

And taking Mr. Holzman's information (I've done a lot of concrete unit weights, and they were all between 145-150lbs per cubic foot), concrete in a four inch slab would weight 50lbs per square foot, given a 4" slab thickness. This doesn't take into account structural steel, but you get the idea. 

Okay, so I just read you want 1/4-1/2"? You can't. Just tile it.


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## SER56 (Jan 18, 2012)

Perhaps I am missing something, but why not just install 1/2" cement board and tile over that (assuming you already have a subfloor in place)?


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## overlooker (Mar 7, 2011)

I can't stand tile floors. Concrete looks really great--that's why I want it. Thanks to those who gave me the means to calculate the weight.


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## SER56 (Jan 18, 2012)

overlooker said:


> I can't stand tile floors. Concrete looks really great--that's why I want it.


Gotcha :thumbup: So I was missing something!


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## stadry (Jun 20, 2009)

the right conc is more important - polymer-modified conc ( grey/white cement, water, fine aggregate [ silica carbide ] - 8' x 10' bathroom mtls weighwhich won't challenge anyone's floor joist system :no: expanded wire mesh sheets stapled to the 15# felt-papered wood floor, 15# felt paper - pool trowel, squeegee, waterproof tape, etc - compressive strength 5,600 - flexural 700 - tensile 260 - most decorative conc artisans do this work every day as did i 'fore retirement - if you want pics, elitecrete.com or any other dec conc mfg'er has 'em :thumbup:

no financial int


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## Canarywood1 (May 5, 2012)

You might want to look into light weight concrete,wich has an in place density of 90-115lbs a cubic foot as opposed to regular concrete with in place density of 140-150lbs a cubic foot, it weighs in at 3000lbs per cubic yard opposed to 4000lbs for regular concrete.


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## stadry (Jun 20, 2009)

lite weight gets its advantage from lighter coarse aggregate whilewtr, cement, & fine aggregate are the same + its a large PITA :yes: placing & finishing it in a small confined space,,, even a thin conc floor is much more difficult than a thin o'lay posted earlier + no risk of random cracking,,, IF you're considering in-floor elec heat, the o'lay is an excellent medium for it,,, you don't have elevation troubles, either, as, at the most, the total thickness is only 1/2",,, can't get that out of conc as most define it.

many aren't aware of possibilities 'cause apron/vest stores don't sell the stuff & 
arch/engineers see it as more decorative than structural,,, its easier to decorate than ' normal ' conc, lighter, & stronger


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## cleveman (Dec 17, 2011)

Question for the engineers:

If the concrete was placed in a 12x24 room, with the 12 dimension having bearing walls, how much of the 50 lbs/square foot could be figured to be transferred to the foundation? 

I'm just thinking if the concrete supported itself, like a piece of plate metal, maybe most of the weight is transferred down on the perimeter and not on the floor joists at all.


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## Daniel Holzman (Mar 10, 2009)

A four inch thick concrete slab does not support itself, even if reinforced with steel. For purposes of analysis, you should assume that all of the concrete weight is carried by the joists, and none by the walls.


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## concretemasonry (Oct 10, 2006)

cleveman -

There must be something to support your mythical self-supporting thin slab that deflects and ultimately finds a load path downward. The thinner the concrete, the more the deflection (and cracks), the more is transferred to the floors. The load goes to the floors. In any event, something has to hold up the structure in some way.

The floor load is transmitted to the joists and beams and into the walls, then down to footings and eventually into the supporting soil.

Dick


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