Slab Repair after plumbing repair

Old 12-18-07, 09:49 PM
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Slab Repair after plumbing repair

Well, as it often goes, one small project has become a beast. Was repointing grout one minute, the next minute having to reframe bathrooms, now the slab has to be opened up for supply and drain plumbing issues. Turns out my p-trap for the shower was rusted out and needs replacement. To do so, the slab has been opened up to access the trap. Well, now that we can see under the slab, it appears that the 1/2 inch copper servicing 6 fixtures has joints all over the place under the slab and looks like there is a leak. I was tempted to change the p-trap and cover things back up, but I want to do this home renovation right, so I am going to re-pipe the house.

Questions for this forum, what is the best way to repair trenches created in the slab? Fibercrete? Rebar? Replace the liner?

Also, is copper required for the plumbing or could I go with a plastic of some type?

What about cutting the trench? Could I saw it as opposed to using a Jackhammer?

Thanks for any info you can provide!

Old 12-19-07, 10:38 AM
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Yes you could use a saw provided you aren't worried about the dust it will create and it will be a lot. Even if you get one of the water cooled ones from a rental place it will kick up a lot of dust as the water is to cool the blade and not designed to stop all of the dust.

The benefit of the jack hammer is you can follow the direction of the pipe by starting at the bad piece and following the pipe to a joint where you can tie into. A saw will allow you to cut a straight line, but if the pipe isn't under the area you scored in the concrete, it does you no good.

I would check with your local pluming inspection office to verify what is acceptable under a slab as far as water supply pipe. You are doing yourself a big favor by cleaning up the mess now as your water bill will skyrocket if that leak gets worse and you might not ever find the location if you hadn't dug up for the trap.

As far a the replacement concrete, make sure the drain pipe is well supported with the proper slope. Easiest to do this with gravel and not dirt. Cover the pipe with more gravel to the base of the current slab and use a good quality bag mix. You could buy an additional bag of cement to add some more cement to the bag concrete to strengthen it, but this isn't necessary.

Don't think your adding rebar or mesh will solve anything as it won't be tied into the remaining slab. Replacing the "liner" which I assume you mean the plastic sheating under the slab will not work, because it won't be tied into the remaining plastic either.
Old 12-28-07, 05:38 AM
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I put a bathroom in our basement and cut piping trenches and finished it all back to a smooth floor, so here's my 2 cents:

I mostly agree with sgtgerryf except that a jackhammer is going to give you a horrible edge to your trenches (if you care) and may leave stress cracks in neighboring concrete areas.

I rented an electric 14" concrete saw and my wife kept the water hose on the blade to minimize dust in the tented area we created. But yes as sgtgerryf said, we still had dust (we were wearing respirators). Once all the trenches were cut, we then jackhammered out the unwanted areas. After all the plumbing was inspected, we packed the pipes solidly in stone and then closed the trenches.

Rebar is very important - not for strengthening the new concrete, but for tying the new to the old. Going on the advice of the concrete trade assoc., I drilled 1/2" holes horizontally every 3 feet around the trench perimeter. I then hammered rebar "dowels" into the holes sticking out over the trenches. When we poured the new concrete, the rebar tied the new/old together.

Around 1-1/2 years later, there's not even a single tiny spider crack.

I hope that helps!
Old 03-18-08, 08:27 AM
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Reading with interest

I too have a plumbing fix under my slab and I am trying to get the right person lined up to do the work or play a huge role in the fix.

I was told by a plumber that if you pack rock or gravel around pipes and then concrete, the rocks will wear a hole in the pipes over time. Did you hear this from anyone or can you dispel this?

I had a camera run in my clean out and i have a broken fitting just in front of my sink. I need to break in the concrete and replace the fitting. It is about 20" down. I also want to put in a new drain line that will allow me to move my W/D to a new location about 5' down the wall from the current location. So the fitting involves a drill down hole and then the new w/d will require a trench to add new drain pipe for Washer and maybe a drill down hole to cap off the old drain line for the washer.
Old 03-18-08, 09:55 AM
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two things without reading the previous replies thoroughly so they may have already been answered.

1. gravel around the pipe. I am an electrician and it is against code to allow large rock to touch the pipes due to the wearing a hole in the pipe.

If you do use gravel, I would suggest pea gravel as it is rounded. I do not see this presenting a problem but I would check with your local code office as this is probably code controlled.

2. when you pour your repair patch. You need to drill horizontal holes in the old 'crete and install pieces of rebar with half in the old slab and the remainder poking into the area where the new pour will be. This will tie he two sections of 'crete together and prevent either section from rising/falling seperately.

as to reinforcing with rebar etc. I am not a concrete person but I have seen huge amounts poured during the course of my work. I have seen very little poured without some sort or reinforcing installed. In a pour suck as this mesh is typically used. It is either supported prior to the pour or lifted after the pour so it is in the middle of the slab and not on the bottom, where it will do no good.

Repairing any vapor barrier should also be done prior to the poor.

The ground should be compacted very thoroughly before pouring as well. Poor compaction now will show up as cracks or unequal settling later.
Old 03-18-08, 10:16 AM
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round stone for backfill,,,

then compaction's much easier,,, yes, vapor barrier even if it doesn't ' tie in ' to the original,,, wire mesh centered vertically ( +/- 5% per aci ) adds tensile strength to conc while its going from plastic thru ' green ' to cure,,, after that, it holds the broken pieces together fiber's an individual choice but i wouldn't use it in my home.

its more important to place contraction joints properly,,, as tscar once noted, its ' controlled cracking '

the lateral pcs of rebar ( tie bars ) aren't nec imn-s-hfo but can't hurt,,, compaction's more important than they are,,, normally 1 side would be either epoxied into place OR the free end coat'd w/grease but many don't bother & their conc's still there.

once cured, there's normally little expansion/contraction of conc due to fairly constant temps.

just my $ 0.03

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