Poured Concrete Walls- What's Normal

Originally Posted By: Chuck Pere
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I’m having a home addition with basement done. The foundation is using a T footing with 10" poured 8 ft. concrete walls. Only horizontal rebar top and bottom. The walls have a couple pour lines that run at an angle. They also have lots of suface defects like honeycombs and large pitting. The contractor did not vibrate the concrete into the forms.


I guess I expected to see smooth walls. The contractor says what I have is normal. He will fill the surface defects on the interior side and the exterior will have damp proofing applied. My question is are smooth walls the norm? Or are some pour lines and surface defects to be expected?

Also he wants to backfill before installing the floor joists and the walls about 6 days old. I've read that backfilling should not be done until the floor is installed for additional support. This seems logical to me but the contractor says that isn't how it's done in the real world. Is it true that most homes are built with backfilling prior to floor installation?

Thanks for any help,
Chuck


Originally Posted By: lewens
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Chuck


First of all, get your hands on a set of plans and see what the designer has to say about damproofing, vibrating the concrete etc. it should be in the margins or on an detail sheet. Putting in the floor before back filling is a given, as far as I am concerned. Any support you can give a new concrete pour is always a wise move. The horizontal lines are the result of what is called a cold pour, caused by one part of the foundation setting up before the next truck arrived and while it is usually not a structural issue will allow water penetration along the seam. Damp proofing will not eliminate the water penetration issue. It will leak. A proper membrane applied to the exterior of the foundation and weeping tile properly installed will go a long way to correcting this problem.


Don’t let the contractor tell you it is a safety issue about backfilling, I have always built the floor and usually the walls before backfilling. The framers have to be careful not to fall in the hole but that is the way it goes. I myself have stepped off into nothingness but believe me you don’t do it twice. There is no reason I can think of that, if he can get a machine in there now, he can’t get it in there later.


Just my 12.5 Cents


You will no doubt here more on this subject as there are always differing opinions.


Larry



Just my usual 12.5 cents


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Originally Posted By: lkage
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Quote:
Also he wants to backfill before installing the floor joists and the walls about 6 days old.


Not a good plan.

Quote:
I've read that backfilling should not be done until the floor is installed for additional support.


What you've read is correct.

Quote:
Is it true that most homes are built with backfilling prior to floor installation?


No.

Really, Larry E. gave good advice when he said to see what the plans/designer says. But if the builder balks at following the design criteria, talk to your local construction code official.


--
"I have never met a man so ignorant that I couldn't learn something from him."
Galileo Galilei

Originally Posted By: dvalley
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Chuck,


Welcome to the NACHI forum.

In residential foundations, concrete walls often are designed to act as beams supported at the top and bottom to resist horizontal loads. The bottom support is there at the beginning of wall placement, but the top support is provided only by the installation of floor joists.

Backfilling foundation walls before installing the joists may result in failure simply because that top support is not there. In short, if your Contractor is in a hurry to begin backfilling, I suggest you work with an engineer to understand whether concrete strength or wall stability is likely to be the controlling factor, and determine when backfilling can commence.

Good Luck with your addition.


--
David Valley
MAB Member

Massachusetts Certified Home Inspections
http://www.masscertified.com

"Some cause happiness wherever they go; others, whenever they go."

Originally Posted By: ddivito
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Get another contractor. If he doesn’t know basic building practices for the foundation, god knows what he’ll do on the rest of the project.


Originally Posted By: John Bowman
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http://www.askthebuilder.com/569_Backfilling_a_Foundation_Wall.shtml


Originally Posted By: mcyr
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Hi Chuck;


Larry is right on his advice to you on your question.

I would like to add that any foundation poured that shows these lines is definitely a sign of waiting for trucks or other element variation.
Most of the time it is due to waiting for concrete trucks to arrive, and the improper vibrating of the concrete when the pour resumed.
Vibration in this case should penetrate the previous pour by at least 6-8 inches to consolidate the two layers, fresh and old. The angle of this cold joint line will also indicate at which slump the concrete was poured at. The standard 4" slump would indicate a cold joint line of about 45- 50 degrees. any less would indicate a concrete slump that would flag the excessive water cement ratio, that exceeded .35 to 1. Most residential foundations in this area comprise of 8" in depth and use 2500 PSI concrete with two # 4 bars at top and bottom.
I definitely wood want the floor framing installed before backfill and also the basement floor which is as critical to wall assembly.

In 14 days, 2500 psi concrete will achieve about 72-75% of it's design strength. This relates to about 1800-1900 psi. I definitely would not backfill these walls even at 7 days without lateral stability provided by the floor framing and also the basement floor.

The honeycombs you indicated in the walls were caused by not properly vibrating and that is why the walls are not smooth as you imagined.
This can be repaired with a parging of cementous product to fill in the cavities. If these areas are present on the backfill side, it should also be filled with a cementous based product prior to a sustainable waterproofing membrane as Larry indicated.

A residential foundation is not a retaining wall. It is not designed to do so.
Any backfill prior to the house framing being done to provide the proper lateral stability, is asking for a problem.

Hope this helps.
Marcel