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JCNelson 02-04-2013 06:48 AM

Slab crack
2 Attachment(s)
Hi all,

I've read all the related threads on this forum and would just like your opinion on a proposed solution to my problem. In a small barn => rental cottage I've just bought, the slab (about 25' x 15') is cracked in two directions, per the photos. The history is of a water leak from burst plumbing above (hence the peeling walls), with the water probably seeping around the slab into the improperly (that is, un-) tamped soil below and causing the edges of the slab to subside.

A handyman who claims to be familiar with the history claims to have consulted a concrete expert and been advised to cut out about an inch (wide and deep) of concrete along the crack (with undercutting) and fill the slot with cement and bonding agent. Given that the slab is now likely stable on this desert soil, this solution seems consistent with the advice offered here on other slab cracking problems. Just two questions:

1) In the photo where the crack hits the edge of the slab, you can see that the slab appears crowned. Should I try to remove the crown? Am I OK laying padding and carpet, or laminate flooring, over the completed repair without doing so? (That is, will it hold up for a good long time?) This will be a respectable but not a high-end rental.

2) The handyman wants to rent a concrete saw for three days and charge for labor for him and his son plus 12 bags of cement and 4 boxes of bonding agent. This looks to me like about three times the time, equipment, and materials that will be needed. I'm inclined to do it myself with a friend, as it doesn't appear this guy has any more experience with this work than we do.

How does it look to the experts?

inspectorD 02-04-2013 08:18 AM

The guy is a salesman. The slab is already cracked, cutting it now just leaves you with pieces that chip out .
If you want to, there are fillers you can install in the crack that are flexible, this would be your best bet. Try a concrete supply house and talk to them abou what to use in your climate.
I would live with the bump in the floor, it's a rental.
You could also jack the slab up with a company that installes grout fill underneath, I would not spend the $$.
However, you could pour self leveling material on top that may or may not peel off when your done.I'm just guessing you don't have a big moisture issue where you are.Again..don't spend the $$.
Rentals are there to get your best bang for your buck, fix it when you sell it and the market is good.

Other "experts" will be along soon to add to the confusion...or not, good luck.:D

BridgeMan 02-07-2013 12:12 PM

Save your hard-earned $$$, and send the un-handyman packing. If the uneven concrete is noticeable, rent a walk-behind grinder yourself and knock it down. You can also fill the cracks with non-shrink mortar yourself, applied by working it into the cracks with a dense, foam rubber hand float (after you've removed all of the dirt from inside the cracks first, and slightly moistened them with a spray bottle of water).

I spent many a night in Socorro, during my 25-year sentence working for the NM DOT. I remember a fatality on the west frontage road south of town (going to the airport), when one of our timber bridges washed out in a flash flood (woman couldn't stop her car in time).

JCNelson 02-09-2013 12:49 PM

Thanks for the responses. Things are slightly more involved than my post indicated -- the handyman appears to have been protecting himself -- isn't just a quack. Work is still pending and we can't rent an electric walk-behind within 80 miles. But plan to carve out the crack with a diamond blade in a robust circular saw and put in Quikrete nonshrinking grout. Socorro former-NMDOT poster, good to hear from you. I'm actually up the road in Magdalena.

Wuzzat? 02-09-2013 03:48 PM

Can you close the crack by mud jacking one edge of the slab?

BridgeMan 02-10-2013 10:54 AM


If what you call a slab crown is noticeable enough (under pad and carpet) to scare off potential renters, and you don't want to put on the mileage to rent a walk-behind grinder, another option is to knock down the lumps with a large masonry wheel in a 7" angle grinder. Make broad, sweeping strokes while holding the wheel flat (parallel to the floor) to avoid gouging the surface. And wear a decent respirator/face mask, as doing it will kick up lots of concrete dust. I'd open a few windows, wide, while setting a large box fan in the open doorway, blowing outward. And don't forget to fix the swamp cooler feed line in the attic, to prevent future water damage to the walls and carpet.

nealtw 02-10-2013 09:10 PM

Self leveling concrete??

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