Filling in concrete in basement


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Old 09-28-10, 08:35 AM
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Filling in concrete in basement

Hello all,

I had a 20' long x 1' wide x 4" deep (approximately) trench cut out of my basement so I could put a drain in for a wetbar. Could someone please give me some advice on filling this back in? What concrete mix should I get? Or is this really not a DIY kind of job?

Thanks for your help in advance.
 
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Old 09-28-10, 09:10 AM
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Out of the subject I would say that a 20 feet long drain is a very long run. Have you thought about venting this run? Did you try to see if the drain works properly? Do you have a P-trap under the sink?

Regarding the concrete, did you go right thru the slab? If not I would say a few bags of cement / sand / gravel will do the trick. Make sure you wet all existing trench well without leaving pools of water and pour the mixture into the trench.

If you went thru the slab, perhaps some vapour barrier is needed under the drain pipe. Also if the new drain pipe is not ABS you may need some protection to prevent the gravel in the concrete to puncture your drain.

Other members may have a different approach
 
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Old 09-28-10, 10:08 AM
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To make a long story short, I ended up only needing about a 8 foot drain thanks to a lack of communication between contractors. I hired out the plumbing, so I'll have to double check what he used.

They went through the slab, does the vapour barrier go above or below the gravel thats under the slab?

What kind of things did you have in mind for "protection"?

There are lots of different concrete mixes at the local hardware stores, and as you can tell I am a newbie, can you recommend one that would be good for this project?

Thanks again.
 
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Old 09-28-10, 11:58 AM
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Just a standard, inexpensive concrete will work fine for you. Mix it up and put in the trench. Flatten it off with a 2x4 to the top of the existing concrete. After the water is gone from the top smooth it out with a magnesium or steel trowel/float.
 
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Old 09-28-10, 12:11 PM
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sounds good.. thanks man.
 
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Old 10-14-10, 05:37 AM
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I did about 36 square feet myself last year for the first time. I did it with a friend. I recommend that. You could do 20 feet yourself, but a buddy to help is a big help.

I think a great way to mix the concrete is by pouring it and the water mixture onto a sheet of poly (6 mil). Then you and your friend each grab a corner and basically walk back and forth a foot or two at a time. it does an amazing job of mixing the cement really well (there may be vids on youtube of the approach).

Something I did not do--a mistake--was not tamping down the concrete. I did wait for it to semi cure the hour or so and then troweled over with a magnesium float to make it nice at the top, but the concrete itself was very "holey" after the first 3/4 " because I had not pushed it down into itself just after putting it in place (I know this because of a side section I had formed for bathtub, so I can see a cross section of the concrete).

The plastic, btw, goes on top of the gravel and underneath the concrete, absolutely that is where it goes. You can use 6 mil poly (and then use some to mix the concrete per above).

You are going to have some minor cracking between the concrete old and the new. Unavoidable, and no big concern. If you have a rough edge on your old concrete it will help key the new in place. You'll also definitely have a crack or two along the new concrete, since a 20' strip of concrete absolutely will not avoid cracking. There's no way around this and it's no cause for concern.

I recommend the quickrete stuff with the fiberglass fibers in it.

Also, get a mask and despite its uncomfortableness use it. You do not want to be breathing in concrete dust and having it cure in your lungs, which is what it will do if you're breathing in the dust.
 
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Old 10-14-10, 09:17 AM
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If you keep concrete damp for about 10 days, covering it with sand and damping it down every day, it will not crack.
 
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Old 10-14-10, 09:41 AM
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Covering it is a great idea to slow the rate of moisture leaving the concrete, but there is no way a 20'X1'X4" single strip of concrete will not crack. It is guaranteed. It will probably also separate away from the old concrete, although the width shrinkage on concrete only a foot wide is such a tiny amount that he may not notice even looking up close.
 
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Old 10-14-10, 10:48 AM
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Skoob - there is no reason why this repair is guaranteed to crack. It may, or it may not. I put drains under my slab many years ago and though I have slab cracks in my basement, the patches that I put in are not cracked. My guess is that it's because the house has already settled, the patches are narrow and shrinkage cracks are less likely to occur. Also, I made sure the concrete cured slowly. I also used mesh in the repair and that may have helped.

FWIW - I use plastic over curing concrete rather than sand. It's a lot easier rewet the concrete and to clean up after it has cured.
 
 

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