# Proper concrete for footing and stem wall



## Willie T (Jan 29, 2009)

The question is not the material choice - 5,000 far surpasses what you need - but the method of pouring.

You will have 'cold joints', the negatives of which can be largely negated by the use of strong and effective 'keying'. But the problem will come from continuious rebar pieces that will be exposed to moisture, and subject to failure due to eventual rust.

The more logical and secure process might be to be certain all your rebar is contained within the confines of each section of footing replaced. Basically pouring a series of individual 'pad' footings.


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## JayG (Jan 29, 2010)

Thanks for the response Willie. My plan- which is extremely ambitious- is to do a new section each week. Although I haven't taken into account the curing process and if that time frame is possible. But any rate, my plan is to replace each section in the quickest possible time. Do you think that if this is done quickly and the sections of rebar are exposed for the shortest possible amount of time, I will still have problems with moisture negatively effecting the strength?


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## Termite (Apr 13, 2008)

Yes Jay, even if you pour it in lifts a couple hours apart you'll still have cold joints between the pours. The concrete hydrates and begins to cure (and form a crystalline structural bond) immediately when it is placed. Once the water is hydrated out of the concrete, concrete poured against the "dry" or drying concrete will not bond like it should....Cold joint. No way to avoid it other than to pour the footing in one pour and then the wall on top of the footing in another pour. It is commonplace for a wall to be poured on top of a footing as early as a day after placement of the footing. The bond between the footing and the wall isn't critical...You should at least form a keyway in the footing (with a 2x4) to receive part of the bottom of the wall and help with lateral stability of what is effectively a horizontal intentional cold joint. A rubberized waterstop poured into the footing is another option but not as common. 

Plan on pouring the footing in one pour and plan on pouring the wall in another pour. Otherwise you're guaranteed a weakened job.

4 yards is normally available from ready-mix plants. They may charge more since it is a short load, but they'll do it. Many batch plants also offer you-cart concrete in a trailer that you pick up and haul to the site. A really great option is site-mixed concrete that is batched on a truck...Many rental companies and some concrete companies offer this service for jobs such as yours. Last time I used it they charged about $100 per yard.

4 cubic yards is 140 bags of concrete at 2/3 cubic foot per bag. That's a heck of a lot of money and it is a heck of a lot of mixing by hand. You'll regret doing bag mix on a job like this. :no:


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## JayG (Jan 29, 2010)

Well it sounds like doing this in sections isn't such a good idea. I think the problem I'm going to run into with with my initial idea of digging out underneath the existing foundation and semi underpin and then pouring a footing and stem wall in one section is that the foundation will certainly cave in if it isn't done in sections at a time. The existing foundation is a 16 inch concrete slab over buried bricks (house was built in 1896). 

I thought about cart concrete being the best option. I just haven't looked into the availibility of it in my area.


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## Scuba_Dave (Jan 16, 2009)

I did around 20 80 lbs bags 2x - hot tub pad & shed "footing"
It was a PIA both times & back breaking work
I can't imagine doing 140 bags


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## tpolk (Nov 7, 2009)

people underpin large old structures all the time with rebar exposed and cold joints. use some bonding agents at cold joints


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## JayG (Jan 29, 2010)

I'm imagining 140 bags would not be fun. My thought was bags would be easier if I were to do this project in sections. All of your responses have been extremely helpful and have enabled me to do addtional searches and learn more about what I'm trying to accomplish. The idea of a series of pad footings seems to be a viable option. Is it fair to see that a series of pad footings would create a more stable footing and stem well than joining cold joints? Given the great soil stability in my area, I would think this could be the better option. Thanks again for the information. This will be very helpful for me when my structural engineer gives me his final assessment.


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## Mort (Nov 26, 2008)

At my concrete company, we have a 1 yard minimum. You'll get a short load charge, but its worth every penny if the alternative is mixing 140 bags of concrete. I've been to jobs before where they pour the footing, wait about 45 minutes to an hour, then wet the rest of the load up and pour a wall. Doesn't happen too often, but it can be done. Only reason to not do it all in one shot is that the concrete will ooze out of the top of the footing form. If you take steps to eliminate that as a factor, you can do it all at once.

Just make sure your mix has air entrainment. Its not necessary for the footing, but it is for the wall, and won't hurt anything. A 3000 psi mix should be sufficient.


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## walkman (Jan 4, 2009)

If you decide to mix it yourself based on what your engineer tell you, I'd suggest getting a mixer and sell it afterwards on CL. I can do about 20x80# bags in 2 hours using my Kushlan. Make sure you're not placing it in freezing weather. I don't mind it so much as I consider it a gym membership. 

I would definitely go the trailer route if I had a truck big enough to bring it home.


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## Willie T (Jan 29, 2009)

Here's an idea of how you would set up each of the sections... following the numbers, so they will 'KEY' into one another. Of course these are shown separated by10" or so. In reality, they will fit (pour) right into one another.

The 'OPEN-SIDED' sections show where the rebar would run (chairs and cross ties not shown)

As you can see, after the 'odd' numbered sections are poured and stripped, only the sides of the 'even' numbered sections require forms because the hardened parts of the 'odd' sections will make the ends of the forms.

BTW....... These CAN be formed a little differently so that you can just keep them going, one right after the other. But this way allows you to leave the original support walls in place for every other section till you get the new walls built.


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## JayG (Jan 29, 2010)

Wow. Thanks for the visual WillieT. This definitely makes much more sense in my head now. One follow up. What you are describing is for the footing and stem wall together? I'm looking at probably a 50 inch stem wall.


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## tpolk (Nov 7, 2009)

perfect willie:thumbsup: do you have a program that lets you do those or is it from a library of material?


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## Willie T (Jan 29, 2009)

This will give you an idea of how you leave alternating sections of old supporting block in place while you lay up the new wall in between.

You just make sure of two things.

One: You make your footing lengths appropiately spaced multiples of 16" so that they will fully support the new block walls.

Two: You space your new blockwork accurately so you will be able to fill in the missing areas perfectly. (Allow for the mortar joints on each end of the blocks.)

It may take some study to grasp all this.

Also, the alternate way of forming the footing sections (I mentioned it above) is shown in the foreground.


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## Willie T (Jan 29, 2009)

tpolk said:


> perfect willie:thumbsup: do you have a program that lets you do those or is it from a library of material?


I just use SketchUp (the free version). I drew the foundations, but imported the block wall from a library.


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## JayG (Jan 29, 2010)

This is great stuff Willie! I was planning on doing a poured concrete stem wall. I'm guessing a poured concrete stem wall is a little bit more difficult to do than block.


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## Willie T (Jan 29, 2009)

It's going to be a bit more difficult, especially stripping off that inside form piece after the pour, but doable.

You will need to modify a "Trimmy" such as this one to be sure you get the forms fillled all the way up. It will have to be mounted to the side of the wall, not the top as it is here, however.


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## Willie T (Jan 29, 2009)

Just so you are aware. There are various other ways to accomplish what you are looking for.

Not knowing all the particulars about your existing construction, it is impossible to go into all of them. But don't limit yourself to just one way of approaching your problem.

This (below) is probably the best way. Support it all on jacks, then remove and replace all the foundation at one time. I only drew this with minimal support so you could get the idea. It would take doubled lumber and likely more jacking locations.

And, yes, you COULD just simply eliminate the steel beams, and run a line of jacks down the inside, under the house, as another alternative method.


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## JayG (Jan 29, 2010)

When I was thinking about pouring the stem wall today, one issue comes to mind. I would still need to do the stem wall in sections just like the footing (with my original plan). Would this be a problem since it would create another series of cold joints? Also, when creating the keys at the footing joints, would six inches be sufficient?


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