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Old 12-21-2010, 08:08 AM   #1
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how to plug a hole in concrete


For those who've not bumped into me before, I'm in the throes of renovating a circa 1970 house that was badly neglected. Several weeks ago I posted a thread asking for help cutting concrete. I posted the lessons I learned, on that thread.

This week, I'm asking for advice on how to plug the holes. I have a trench almost bisecting the basement with a few branch runs and a few extra holes for good measure. About 50' trenched in total.

My objective is to fill the holes with compacted sand, lay my pipe, bury the pipe in sand and wet it down to compact it. When my sand approaches the level of the concrete, I've got to top off the hole with concrete. Hopefully, it will bond with the existing concrete (which additive?) be so smooth as to be unnoticeable and suitable for painting.

The trenching is nice and straight, cut with a diamond saw and is about 4-5" wide. There are a few points where I'm putting a 3"x3"x3" WYE that is larger and there are some points where a square hole was cut into the concrete to introduce sewers and address other problems that haven't been filled in. I also have an old floor drain that has to be removed.

Any suggestions would be appreciated.

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Old 12-21-2010, 10:18 AM   #2
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how to plug a hole in concrete


The plan sounds good. Just a few thoughts. You need to compact the sand using a plate whacker or a hand tamper. Wetting the sand is fine, but wetting alone will not compact the sand, it simply allows the compaction tool to work better. Maximum six inch lifts for compaction.

The Thoro corporation makes an entire line of products designed to bond concrete to concrete, check out their products. If you are placing a thin lift of concrete, say 3 inches or less, the most important issue in terms of appearance is crack control, which can be handled by proper placement and keeping the concrete moist while it cures. I like to use moistened burlap bags over the concrete as means of minimizing cracking. Since the placement is relatively narrow, there is no need for control joints.

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Old 12-21-2010, 05:00 PM   #3
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how to plug a hole in concrete


Hi Daniel:

Thanks for the comments.

Quote:
Originally Posted by Daniel Holzman View Post
The plan sounds good. Just a few thoughts. You need to compact the sand using a plate whacker or a hand tamper. Wetting the sand is fine, but wetting alone will not compact the sand, it simply allows the compaction tool to work better. Maximum six inch lifts for compaction.
There will only be 2-6" of sand on top of the 3" ABS pipe that I'm burying so I don't want to compact too much on top. I was hoping that if I compacted below and wet above, I'd be fine. I guess not huh? Now I just have to figure out how to compact on top of the pipe. Hmmmm, back to the drawing board.

Quote:
The Thoro corporation makes an entire line of products designed to bond concrete to concrete, check out their products. If you are placing a thin lift of concrete, say 3 inches or less, the most important issue in terms of appearance is crack control, which can be handled by proper placement and keeping the concrete moist while it cures. I like to use moistened burlap bags over the concrete as means of minimizing cracking. Since the placement is relatively narrow, there is no need for control joints.
I finally found the Thoro site ( http://www.thoroproducts.com/products_accessory.htm ) and found "Acryl 60." So, now I know what I'm looking for and I'll hit the local retailers. Wish me luck.
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Old 12-22-2010, 05:22 AM   #4
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how to plug a hole in concrete


if its only that wide, walking on it will compact it just as well,,, being that narrow won't let anything in anyway,,, not to be disagreeable but, in my experience, sand doesn't lend itself to power compaction & damned little compaction of any type,,, various types of soils/dirts will but sand don't

since the pipe chase is diamond sawed full depth ( a mistake, imo ), clean it well of remaining conc laitance,,, using a bonding agent's good - mortar mix applied to pre-wetted side surface,,, for the quan you need, apron store,,, unless you're using the floor for decorative purposes post-repair, don't worry about contraction jnts as the conc'll crk where it wants
3" is close to std thickness for res bsmt floors.
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if you hear it from a guy in the apron store, be VERY suspicious the mtl/method will work,,, when it time to build something together, they won't answer phones NOR help

Last edited by itsreallyconc; 12-22-2010 at 05:26 AM.
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Old 12-22-2010, 08:14 AM   #5
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how to plug a hole in concrete


Since you only have a few inches of sand over the ABS, you can compact using a block of wood and an 6 lb sledge. Put the three inches of sand over the pipe, lay the block over the sand, and tap it a few times with the sledge. Move the block along, repeat. I use about an 8 inch long block Works great, I did the same thing when I put my drain line in the basement.

As noted, compacting sand or gravel is more difficult than compacting finer grained soil, but it does work, especially if the sand is moist. It may not be obvious, but sand will compact.
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Old 12-22-2010, 10:21 AM   #6
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how to plug a hole in concrete


true, sand does compact to an extent but i wouldn't want to build roads on it,,, gravel's different ( eg, NYSDOT item 6 ),,, even in ga & sc, we use sand/clay which is NOT sand,,, merry Christmas to all ! ! !
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Old 12-22-2010, 06:00 PM   #7
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how to plug a hole in concrete


Thanks very much Gentlemen.

I'm pulling the old pipe right now and finding out what BNQ is. Hope to have the new floor laid early in the new year. We're hosting a crowd on New Year's day! In the middle of construction too. Wish me luck!
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Old 12-23-2010, 12:55 PM   #8
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how to plug a hole in concrete


I'd personally skip the sand all together (unless you already have it) and simply use a clear stone, like #1 washed stone or #1 fractured stone. No compacting required at these minimal depths.

As for the bonding agent, I would skip it in this scenario, as it will do nothing as the concrete shrinks ever-so-slightly away from the existing. Dowels out of 3/8" rebar, pole barn nails, etc... every few feet along both sides of the trench will do an adequate job.

As for the finishing itself, it's certainly not easy to blend it in w/o being able to notice it later. The patch will have a tenancy to shrink away, sowing a distinct line on each side. Possibly, a few quotes of paint may blend it in better so it's not noticeable. The hardest part of the patch will be keeping the cream off of the existing slab wile still closing up the edges of the patch.
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Old 12-23-2010, 02:32 PM   #9
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how to plug a hole in concrete


Hi Jomama45:

Quote:
Originally Posted by jomama45 View Post
I'd personally skip the sand all together (unless you already have it) and simply use a clear stone, like #1 washed stone or #1 fractured stone. No compacting required at these minimal depths.
I'm putting down cell-core ABS which is fine for burying but can't take a lot of pounding. That's what I've learned so far, I hope it got it straight. In order to make room for the pipe, I've been removing and sifting the sharp concrete bits out of the sand and chucking the stones and concrete and stockpiling the sand. I've also got several tonnes of sand in the back yard waiting for a job or disposal.

Can't get stone or stone dust until spring. It's buried under several feet of snow.

Quote:
As for the bonding agent, I would skip it in this scenario, as it will do nothing as the concrete shrinks ever-so-slightly away from the existing. Dowels out of 3/8" rebar, pole barn nails, etc... every few feet along both sides of the trench will do an adequate job.
Here's where I was hoping to lay the concrete slightly curved above the existing floor so it will shrink down to the level of the floor. I was thinking about 1/8" "crown." Is this a good idea?

Quote:
As for the finishing itself, it's certainly not easy to blend it in w/o being able to notice it later. The patch will have a tenancy to shrink away, sowing a distinct line on each side. Possibly, a few quotes of paint may blend it in better so it's not noticeable. The hardest part of the patch will be keeping the cream off of the existing slab wile still closing up the edges of the patch.
What happens if I "sort of" spread the cream slightly too far? I was thinking I'd feather off with a brush or something. Not a good idea?

Thanks for the help gentlemen. And may I take this opportunity to wish each and every one a very merry Christmas and a Happy New Year.

Talk again in 2011;-)

Ron

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