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bolumenb

06:31PM | 05/12/02
Member Since: 05/11/02
19 lifetime posts
Bvbasement
I will be building a new home in about 2 months and plan on using a 12" poured wall. I am planning footers of 24" x 12".
Questions:
1) Do I need any rebar on the footers or can they be just plain concrete? Soil is in Ohio (clay and some sand).
2) Do I need a keyway (2"x4") in the footer prior to poured wall? If so, why?
3) Do I need vertical rebars in the poured walls?
4) How do I know what concrete I should use and how do I know the vendor is supplying the proper concrete. I am thinking of 6 bag mix but also limit the water to 5 or 5.5 gallons to get about 3,000 psi but how do I know that the mix is fine out of the truck and how do I really control the water used by the workers?

Thanks,
Bill

GlennG

05:43PM | 05/15/02
1. Use at least 3 - #5 rebars continuous with a 22” overlap at any splice joints. Use #3 rebars for cross ties every 24” O. C.
2. Yes you should use a keyway in the footing to prevent movement from soil and hydrostatic pressure against the wall and as added insurance in the event the rebars rust through at the joint.
3. You should have #5 vertical rebars (bent dowels) that are embedded in the footing and stick up at least 22” above the footing. Tie additional rebars to them as needed. Horizontal bars should also be used to create a vertical “mat”. Ties the bars at 12” O. C. each way max.
4. When ordering the concrete, tell the plant to send it at a 3”– 4” slump max. Be sure to use a mechanical vibrator when placing the concrete to minimize any air pockets or honeycomb. To be certain you are getting the quality of concrete you order, and to control the addition of water after it leaves the plant, you should hire a soil & materials engineering firm to send a technician to the job for each concrete pour. They will make test cylinders and verify the air entrainment and slump of the concrete as it is being placed. The slump test is used to control the amount of water that can be added. A 4” slump should be the maximum allowed. The more water the greater the slump. The test cylinders will be “broken” in a hydraulic press at 7 and 30 days to test the compressive strength of the concrete as it cures. It should reach the 3000 lbs. Strength within the 30 days.

Good luck,
Glenn Good

[This message has been edited by GlennG (edited May 15, 2002).]

bolumenb

12:52PM | 05/19/02
Member Since: 05/11/02
19 lifetime posts
1. How important is "Use #3 rebars for cross ties every 24” O. C." - I have a hard time getting anyone to even use rebars on footers lengthwise much less crossties.
2. O.K..
3. I assume these vertical rebars go in the keyway (center of the footer)? How do I know when I need to "Tie additional rebars to them as needed".
Where do I tie these "Horizontal bars should also be used to create a vertical “mat”" to?
Please explain this step a bit more as I understand the vertical rebars but not the horizontal where they would go on a poured wall which has forms that concrete is poured into the forms.
4. O.K. but can't I just take a sample myself and measure the slump?
Does anyone goes through a test to measure the strength of the concrete? I understand that this the right thing to do but will the concrete company work with a homeowner to do this test?
Thanks a million.
Bill

GlennG

06:13PM | 05/19/02
Many contractors will not use rebar unless an engineer or inspector forces them to. It takes some time and cost money but it is important if you want the foundation to be sound and to last. Without using the rebar you may likely get some cracking in the foundation walls that are carry troughs from the footing. The #3 crossties act as a brace to hold the #5s in the proper position and will help stabilize them when the concrete is being poured. They also help prevent longitudinal cracks from forming in the footing. You can do without them, but the overall job will not be as strong. You could tie the bars together yourself if the contractor will take a few minutes to show you how. It is not very difficult. When the mats are tied together you should place them in the trench and lay them on some 2x4x8 concrete bricks to hold them up off the ground. Then when the concrete is poured over them they will be in the proper location. (2-3 inches from the bottom of the footing.)

If the foundation wall is higher than the vertical dowels you embedded in the footing you will have to tie additional rods to them to make up the proper length to match the overall height of the wall.

The horizontal rebars are tied every 12” OC across the vertical bars making a vertical mat between the wall forms.

To measure the slump in concrete requires a test cone and instruction in the proper testing procedure. It is not likely you can do it yourself. If the concrete is too stiff and the finishers need to add more water, you need to know how much you can add based on the quantity in the truck and the slump. If you mistakenly add too much water you will ruin the load of concrete. An experienced “soil & materials” engineering firm should do this for you if you want it done properly. They will also make the concrete test cylinders that will be used to test the overall strength of the concrete.

Glenn Good

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