concrete slab repair

Old 10-13-07, 07:34 AM
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Join Date: Oct 2005
Location: Florida
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concrete slab repair

Hi I used a jack hammer to open the 4" concrete slab and made a trench for the plumber to come to redo the underground cast iron pipe fittings.

Once they are done I need to pour the concrete slab back.

Question I have is...

(1) As I broke off the old concrete slab, there were a lot of the large chunks of concrete I have as debris. Should I use some of those to fill in the trench up to the 4" mark below grade then fill the void with sand, or should I use pure sand and pack them tight?

(2) There were wire mesh inside the concrete slab that I broke up. The trench is about 8" to 12" wide about 10 feet long. Is there anything I need to do as far as the wire mesh? Should I cut another wire mesh of that size and put it in? Should I drill holes on both sides of the slab and insert rebars in between? The way many of them broke off I am not sure I can tie back to the old ones.

(3) Underneath the concrete slab is a sheet of plastic, is that a moisture barrier? Now that seal is broken what can I do to have the same effect? There are only a few spots with the edge of the plastic dangling out most of it is torn right at the edge where the concrete broke off. Do I get another sheet same size to toss it in, or should I fill sand up to the 4" mark, then pour a thin layer of something (what?) that will seal in the bottom of the concrete?

Old 10-13-07, 07:46 PM
Join Date: Dec 2001
Location: Volusia County, Florida (Central)
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Since you appear to be in Florida, your "issues" are familiar.

The best way is marrying the existing slab to the part you tore up and don't use the old pieces that are broken up.

If you can, get a hand tamper or since it isn't too big use a sledge hammer (pound down with the broad top of the hammer) to compact the soil so it isn't loose. Wet the soil first to make it compress more easy.

If possible, drill a six inch hole with a masonary bit approx every 6' in the old slab on both sides and put epoxy (Simpson brand...., in where the Simpson Strong Tie materials are....Home Depot, Lowes) in the hole and a piece of rebar in it extending at least 6" into the part you'll pour, more length if you can. If you only have 4" of slab, use 1/2" rebar. The point is to tie the old to the new. A Milwaulkee bit from Ace Hardware is cheap and the best I know at more than half the price. If you can't drill it straight, the drill at an angle, but it is important to add the rebar so the new is strongly tied to the old.

The plastic barrier was to hold in and protect the termite protection from the water in the concrete (also helps keep the water consistency in the concrete for extremely dry soil) put in before the original slab was to be poured.

If the the home is more than 7 years old and/or the soil was removed and new added, it would be best to get someone to add some termite treatment (Termidor) which at the most shouldn't cost more than 30 cents a sq ft. Some areas sell a Borax mixture which is also effective and mostly used where the well is <25' from the treated area. If you have a well, and it is less than 25' from the area you're treating, then don't use Termidor (so I'm told). The visqueen should be 6 mil. to meet code must be taped together ( in your case with the old, common duct tape will do). If too ragged to tape to the old, lay it in and add a latex caulk and just try to seal it best you can.

Rather than put grid or rebar back in and since it isn't a footer , use fibercrete which is usually no more than $6 per yard more at 2500psi or more ( I personally use 3000psi fibercrete). Fibercrete @ 2500psi minimum meets code in Florida and if used, steel isn't required imbedded in the concrete (except for footers). By the way, DOT also approves Fibercrete for aprons. If you're going to mix and pour yourself, Fibercrete is available at the home centers.

Now, you may say that why should I pay attention to code?
Recent litigation has indicated that insurance companies and home inspectors have been asking how things are done and can use it to either refuse a claim, or negotiate a lower price if code isn't followed, besides the peace of mind of doing the job right has worth.

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