# Patching Concrete Slab after Plumbing Work



## kktalker (Aug 13, 2017)

I'm doing a kitchen renovation, moving an island sink to a new island location, as well as adding two dishwashers and an icemaker to the island. I am a moderately-capable DIY-er, but I hired a contractor for this job because my life is more busy than usual at this time. Well, the contractor walked mid-job, so I'll be GC-ing after all. :glare: 

Just prior to the contractor ending work, his plumbing and electrical subs had passed their rough inspections, then his demo guy covered up the work in preparation for patching the slab. The pictures below (see next post) are how the contractor left the work. I didn't watch the holes get filled, but I don't think there is gravel under the pipes. I do know the demo guy took two days to backfill, filling partially one day, wetting it down, then filling more the second day. Overall, I'd say the plumber, electrician, and demo guy were all pretty reliable, though at this point--based on what I know about the contractor and other parts of the job--I am wary of corners being cut.

Tile and island cabinets with quartz countertop will sit on these patches. Here are my questions:

1) There are new stress fractures from each corner of the two holes. Do I need to be concerned about these, or just rely on my decoupling membrane when I tile?
2) Do the stub-outs look like they are wrapped appropriately for the pour, and can I pour right up to the wrapping? (The square thing covered by cardboard is a floor drain for the icemaker.)
3) What do I need as vapor barrier, and do I need to dig out under the surrounding slab to overlap it?
4) Should I use rebar dowels to tie the old slab to the patch? Do I need a concrete bonding liquid on the slab edge, or just wet it before pouring?
5) I'm not sure whether I want to just pour from here, or dig up to make sure the demo guy backfilled properly. What would you do?

Thank you for your time.


----------



## kktalker (Aug 13, 2017)

Here are the pictures.


----------



## Guap0_ (Dec 2, 2017)

They should have saw cut the floor before chopping. That could be what made the cracks. I would square the holes with a saw, compact the dirt evenly & pour a concrete ready mix or type S mortar mix. Use a bonding agent.


----------



## kktalker (Aug 13, 2017)

Thank you, Guapo. Can you tell me the purpose of square-cutting the hole? Wouldn't I want to leave the edges jagged to key the new patch to the old slab?

And you are saying no vapor barrier is needed?


----------



## Guap0_ (Dec 2, 2017)

Was there a vapor barrier under the slab that got destroyed when they chopped the floor? There are pros & cons on vapor barriers, under a slab.
https://www.wagnermeters.com/getting_the_vapors/

I guess that it isn't totally necessary to square the edges although that's what should have been done. At the very least, I would dig around the edges. I don't like the way the dirt slopes upwards. I would want at least 2 inches depth. There is less chance of cracking. Make sure that you coat the edges with a bonding agent & I would put some in the mix as well.


----------



## stadry (Jun 20, 2009)

*square cut patches certainly look a helluva lot better + reduce odds of random crking,,, haven't heard any cons from no vapor barriers - neither from engineer, designer, OR specifier,,, undercutting conc always aids in patch longevity,,, whatever your floor's final finish will determine how best to fill voids,,, probably not nec to use dowels - how thick's existing floor ?*


----------



## kktalker (Aug 13, 2017)

Thanks, guys. Guapo, yes, there was a vapor barrier there. Stadry, existing floor is about 4" I believe. The flooring will be tile.


----------



## Guap0_ (Dec 2, 2017)

Since a vapor barrier existed, it can't hurt to replace it.


----------



## jomama45 (Nov 13, 2008)

kktalker said:


> 1) There are new stress fractures from each corner of the two holes. Do I need to be concerned about these, or just rely on my decoupling membrane when I tile?
> 
> I wouldn't be concerned if you're using a decoupling membrane.
> 
> ...


If I was worried about settling, I would just dowel the patch into the slab. Don't pour less than 3" thick for the patch.


----------

