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-   -   What is the minimum depth you can pour a basement floor? (http://www.diychatroom.com/f19/what-minimum-depth-you-can-pour-basement-floor-149359/)

tibberous 07-06-2012 10:52 AM

What is the minimum depth you can pour a basement floor?
 
Without it cracking?

gregzoll 07-06-2012 11:11 AM

Depends on where you are locating the body. Who knows, since you need to be asking the local AHJ what is required by code.

Joe Carola 07-06-2012 12:09 PM

Quote:

Originally Posted by tibberous
Without it cracking?

Call your building department.

wkearney99 07-06-2012 12:19 PM

You mean to do your digging out the basement idea? You're not listening. DO NOT DO THIS YOURSELF.

Start by calling a foundation company and get an estimate for the job. That will give you an idea about how a job like that is done. There may be ways to do some of the work yourself as a cost-saving measure. But that kind of job is NOT a simple one and should not be done without engineered plans and local permit approval.

tibberous 07-06-2012 12:51 PM

Quote:

Originally Posted by wkearney99 (Post 959215)
You mean to do your digging out the basement idea? You're not listening. DO NOT DO THIS YOURSELF.

Start by calling a foundation company and get an estimate for the job. That will give you an idea about how a job like that is done. There may be ways to do some of the work yourself as a cost-saving measure. But that kind of job is NOT a simple one and should not be done without engineered plans and local permit approval.

No offense, but literally every post I make, I ask a simple question, trying to include all relevant information.

Then 20 people tell me not to do it, that I should call a contractor, that it's illegal, to get permits and get an engineer.

And hopefully one or two people will actually answer the question I ask.

Then I do my project, and it will turn out sweet.

So can someone just answer my question:

- I need a 4' x 25' trough, 4" deep, in my basement, at least 2 feet in from the foundation walls. I was going to did a 5' x 26' x 6" deep rectangle. Then I was going to stick in a 4'x25'x6" MDF form, braced to ****, and pour a the outside of my form (6x6) with this:

http://www.homedepot.com/Building-Ma...&storeId=10051

No rebar, just concrete, because it won't freeze or be under pressure.

Then I wanted to pour a 2" floor our of the same stuff.

And then I wanted to either epoxy it or cover it with liquid rubber.

So could some please tell if this will work, or what I could do different - that my house is going to fall in because you need an engineering degree to dig a hold.

wkearney99 07-06-2012 01:17 PM

Just digging a hole... well, that's also how you make a grave.

If you do the project and your house caves in you or your neighbors will have suffered for your willful ignorance. Nothing 'sweet' about that. Did you not go read the web page linked above? The one that shows a house falling over onto it's neighbors? Does the picture not make it clear what the risks are?

There's plenty of times where DIY is a great way to learn, save money and have a sense of pride in workmanship. Digging the basement out from under your house is really NOT one of them.

It's not just the hole that's the issue. It's the load of everything on the foundation. All that dirt outside is pressing inward and the floor helps distribute that sideways load. The weight from above pushing down, again, the lateral strength provided by the floor helps keep the walls from buckling inward. If you take out that floor without a THOROUGH understanding of the loads involved then you WILL risk the house collapsing.

Jobs like this, done properly involve testing the soil first, to see whether it's even safe to proceed. Some soils are not strong enough to let the job be done safely. Then, usually, the job is done one section at a time to underpin the existing foundation to make sure it can handle the loads involved without risking the house shifting or collapsing. Then the slab is replaced, sometimes in sections, again to manage the loads involved.

By hey, you're free to be as bone-headed about it as you like. Just don't let your house fall on your neighbors and don't have anyone else anywhere NEAR the house while you're digging that grave of yours.

Joe Carola 07-06-2012 01:36 PM

Quote:

Originally Posted by tibberous

No offense, but literally every post I make, I ask a simple question, trying to include all relevant information.

Then 20 people tell me not to do it, that I should call a contractor, that it's illegal, to get permits and get an engineer.

And hopefully one or two people will actually answer the question I ask.

Then I do my project, and it will turn out sweet.

So can someone just answer my question:

- I need a 4' x 25' trough, 4" deep, in my basement, at least 2 feet in from the foundation walls. I was going to did a 5' x 26' x 6" deep rectangle. Then I was going to stick in a 4'x25'x6" MDF form, braced to ****, and pour a the outside of my form (6x6) with this:

http://www.homedepot.com/Building-Ma...&storeId=10051

No rebar, just concrete, because it won't freeze or be under pressure.

Then I wanted to pour a 2" floor our of the same stuff.

And then I wanted to either epoxy it or cover it with liquid rubber.

So could some please tell if this will work, or what I could do different - that my house is going to fall in because you need an engineering degree to dig a hold.

Your simple question can be answered by your building department in two seconds. What part of that simple answer don't you understand?

Do you not have a phone? If not drive there and ask in person....its that simple!

AGWhitehouse 07-06-2012 01:48 PM

Most important aspect is a solid base... Also, remember that concrete shrinks as it dries, so you'll need to provide control joints to allow it to crack where and how you want it. If you don't provide the joints, you'll eventually see spider cracks running randomly...

4" is the minimum thickness I'd care to recommend for non-structural uses. 12" is a pretty common thickness for load-bearing slab haunches, though these require rebar to be truly effective at weight distributions.

Canarywood1 07-06-2012 04:48 PM

Quote:

Originally Posted by AGWhitehouse (Post 959273)
Most important aspect is a solid base... Also, remember that concrete shrinks as it dries, so you'll need to provide control joints to allow it to crack where and how you want it. If you don't provide the joints, you'll eventually see spider cracks running randomly...

4" is the minimum thickness I'd care to recommend for non-structural uses. 12" is a pretty common thickness for load-bearing slab haunches, though these require rebar to be truly effective at weight distributions.


He's using shrinkage compensating cement.

GBrackins 07-06-2012 06:08 PM

the minimum thickness for a basement concrete slab is 3-1/2", however I never pour less than 4" for uniform residential loading. I take it you are installing a perimeter drain (french drain)? I always installed a 6 mil polyethelyene vapor barrier under the slab and welded wire fabric in the slab.

AGWhitehouse 07-06-2012 06:41 PM

Quote:

Originally Posted by Canarywood1 (Post 959378)
He's using shrinkage compensating cement.

Fair enough but it is called crack-resistant cement, not crack-proof. Better to anticipate than regret the probable...

Canarywood1 07-06-2012 06:56 PM

Quote:

Originally Posted by AGWhitehouse (Post 959455)
Fair enough but it is called crack-resistant cement, not crack-proof. Better to anticipate than regret the probable...


No such thing as crack proof in concrete,but it sounds like he pouring a chase,so no control joints.

GBrackins 07-06-2012 07:50 PM

Quote:

Originally Posted by tibberous (Post 959234)

- I need a 4' x 25' trough, 4" deep, in my basement, at least 2 feet in from the foundation walls. I was going to did a 5' x 26' x 6" deep rectangle. Then I was going to stick in a 4'x25'x6" MDF form, braced to ****, and pour a the outside of my form (6x6) with this:

No rebar, just concrete, because it won't freeze or be under pressure.

Then I wanted to pour a 2" floor our of the same stuff.
.

sounds like a perimeter drain 4' x 25' trough (which would probably be more than 4" deep) and then a slab (his 2" floor).

tibberous 07-06-2012 10:25 PM

deletete

dalepres 07-07-2012 11:37 PM

Quote:

Originally Posted by AGWhitehouse (Post 959273)
Most important aspect is a solid base... Also, remember that concrete shrinks as it dries, so you'll need to provide control joints to allow it to crack where and how you want it. If you don't provide the joints, you'll eventually see spider cracks running randomly...

4" is the minimum thickness I'd care to recommend for non-structural uses. 12" is a pretty common thickness for load-bearing slab haunches, though these require rebar to be truly effective at weight distributions.

I think you can land commercial aircraft on 12" thick steel reinforced concrete. I think if you got to 6 inches you could put any heavy load likely to be found in a residential basement.


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