Building new home. Question for contractors / home builders about foundation / slab

[pharmvet]

I am about to start construction on a new home. My contractor has discussed with me that he plans to pour my footings one day, leaving re-bar sticking up out of them. He then plans to bend the re-bar over and tie it in with the re-bar that will be in the slab. He plans to pour the slab a day or so later. Everything will be tied together with rebar, but obviously there will be a "cold joint" at the juncture of the footings and slab. Do you feel this is an acceptable method as compared to pouring footings and slab at the same time? Any and all thoughts/ opinions welcome. Thanks!

 

[KennyG]

This is a pretty standard approach. In a commercial/industrial project, the cold joint would be prepared with treatment to get better adhesion, but for residential there may be nothing special done. It may crack, but the rebar will keep it from moving and, because the slab is continuous, you won't have any leakage crack or relative movement under your floor. As long as the base under the slab is properly compacted, shouldn't be a problem.

 

[Streetcar]

The construction joint is common. Field bending the rebar is frowned upon.
For construction joint have the footing water cured and wet the existing concrete prior to placing slab.
There are bonding agents available to increase the joint strength. They look like elmers glue

 

[EddieWalker]

This is done for porches and garages, but not so much for living space. Why is he wanting to do the footings separate from the slab? The reason for doing the porches and sometimes the garage after the living space is poured is because of exposure to the elements compared to a controlled environment inside the house. I rarely see garages done separately anymore, but always the porches.

 

[topbuilder]

Construction practices can be regional...
I've been building nearly 20 years. Never seen anything like that. Never seen an engineered drawing for residential foundations that did not specify continuous pour. The largest residential slab I have done was almost 16,000 square feet. Continuous pour...

 

[747driver]

Lived in southeast Texas for 13 yrs ( Beaumont ). Poured many slabs and footers. This maybe be ok for a free standing garage or shed but not for a house slab. I always poured in one continuous pouring ( monolithic ). Formed everything up leaving the top 4 inches for the slab thickness and then the bottom 16 inches for the continuous footer at 8 inches wide. Always put a bevel on the inside of the footer so the slab would have more bearing placement, otherwise the slab is subject to break at the 90 degree angle where it meets the footer. Rebar all around the footer then tie in the mesh for the slab. Cold joints anywhere are not good and makes it a weak point for separation and cracking. Good luck on your new home !

 

[flusher]

I am about to start construction on a new home. My contractor has discussed with me that he plans to pour my footings one day, leaving re-bar sticking up out of them. He then plans to bend the re-bar over and tie it in with the re-bar that will be in the slab. He plans to pour the slab a day or so later. Everything will be tied together with rebar, but obviously there will be a "cold joint" at the juncture of the footings and slab. Do you feel this is an acceptable method as compared to pouring footings and slab at the same time? Any and all thoughts/ opinions welcome. Thanks!

Here's how my concrete contractor poured a 24x42 ft x 6" thick slab for my shop in June 2005.

4000 psi concrete, 6" thick #4 rebar on 18" centers, 10 mil thick Visqueen plastic barrier under the slab.



No cold joints in that slab.

Good luck

 

[CurlyDave]

I have seen it done both ways.

The advantage to a continuous pour is that the concrete in the slab on top of the footer adds to the strength of the footer. OTOH if the footer only has to be 4" thicker to make up for it. Usually not a big deal.

The advantage to separate pours is that a crack will not usually propagate through the cold joint.

Typically it is allowable to field bend #4 and smaller bar, and I have bent up to #6 bar but being careful to allow a sufficient radius.

If it gives the contractor more time to properly finish the slab, this could be an advantage to you. I would take a better finish over a monolithic pour any day.

 

[topbuilder]

This is done for porches and garages, but not so much for living space. Why is he wanting to do the footings separate from the slab? The reason for doing the porches and sometimes the garage after the living space is poured is because of exposure to the elements compared to a controlled environment inside the house. I rarely see garages done separately anymore, but always the porches.

Porches not part of the slab are considered "flatwork" not a foundation. 1/2 the cost. That would be the only reason I know for pouring them separate. That and the concrete can be ordered with a cheaper mix. 2500 vs 3000 psi.

 

[dmccarty]

Our porches were poured well after most of the house was finished. I never asked why but always assumed that this was to keep the finished porch from getting chipped, painted, or mortar on the finished surface. All of the houses I have seen being built in three states did it this way.

The house foundations were poured and days later the slab was poured. Our land is not flat and the difference in height from the lowest point to the highest point of the slab is about 5 feet. Most people would have built a crawl space but we wanted a slab. The interior of the foundation was filled with 67 stone and after the plumbing was completed and then the slab was poured. Worked just fine. We do have plastic and four inches of rigid insulation under the slab as well.

Later,
Dan