Concrete Ceiling Repair Advice

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Old 01-03-14, 06:24 PM
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Concrete Ceiling Repair Advice

Hello,

The underground garage has a hole (I'm not sure what to call it) in the concrete ceiling. The Condo has gotten some contractors to fill it up a few times, but the filler keeps falling out and causing damage to my car. Luckily, nothing fell on me although I stand under there quite a bit when I get stuff out of the trunk.

I'm not sure what to do. I don't want it filled with stuff that will just fall down again.

I would like to arm my self with some knowledge before asking them to fix it again. Can someone please provide some advice as to how it should be fixed (or leave unfixed) and is there some issues with the previous work that is causing it to fall down? (I don't know much about this stuff)

I can take better pictures if that would help.

Thanks
 
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Old 01-03-14, 08:58 PM
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I've administered and inspected the repair of literally several thousand square feet of deteriorated concrete (much of it overhead), but I'm not exactly sure I can accurately identify what the pix show. The black material around the center wad of exposed concrete almost looks to be bituminous in nature--not good. I'd suggest further evaluation to determine what caused the failure in the first place, as there appears to be a similar failed area to the left of your car. In any event, it appears a "contractor" was chosen for the previous repairs who had little (proper) concrete repair experience. More likely chosen based purely on price--again, not good. If it's any consolation, I've seen many instances of parking garage repairs fail within just a year or two of installation, most of which were performed by professional contractors (having little concrete rehabilitation experience).

A satisfactory repair of concrete requires both using the correct repair product and more importantly, using proper repair site preparation and placement procedures. Including chipping off any and all deleterious materials, delineating the edges of the patch with sawcuts (at least 1/2" deep, and inclined from the vertical by around 15 degrees to form a wedge-effect that will assist in holding the repair concrete in place), installing some reinforcing steel anchorage, sand-blasting the entire area, installing a surface form system that will enable getting the new concrete into place with a minimum of leakage, and finally placing the repair concrete followed by form-stripping and curing. For getting the new product into place, best is access from the top-side; if that's not an option, using a hand grout-pump with a flexible outlet hose can also work. Dry-packing the repair concrete is not recommended for a patch as deep as yours appears to be.

Regarding "arming yourself with more knowledge"--how about putting the owner/manager on notice that getting hit on the head by falling concrete can easily prove fatal, and certainly will cost him far more (in medical expenses and legal fees) than hiring a decent concrete repair specialist would cost.
 
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Old 01-05-14, 12:16 PM
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Thanks for the detailed response. I took another look at it today and took some pictures of the smaller bits. It looks like the dark stuff was just plaster to cover what looks like mortar under that. If they just filled it with mortar, then I'm guessing it will fall out eventually? The hole had some rusting rebars poking out and there is a slight leak from above. (This is in the basement, so above that is just sidewalks and pavement.)

If it matters, it was -20C/-4F on the day it fell down. Both times, the repairs failed in the winter, not even lasting a year. Rather dodgy/dangerous repair job. I'll definitely want to know how they propose to fix it before they start on any work again.
 
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Old 01-05-14, 02:32 PM
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The "dark-colored plaster" applied by someone to contain a leak from above is indicative of a poor repair effort. The source of the leak needs to be determined and then stopped, from above. Trying to contain the moisture from below is foolish.

It looks like dry-pack mortar (indicative by the air voids), with no rock in it. Rock is what gives strength to concrete, making concrete stronger than mortar. Also, it sounds as if corroding rebar at the base of the patch could be a prime source of the patch letting go, as rebar expands considerably when heavily corroded, putting the concrete/mortar under it in tension. Once the leak source is stopped, a proper repair would consist of chipping around any visible rebar, such that the new repair concrete (not mortar) has something to grab onto.
 
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Old 01-05-14, 02:42 PM
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BridgeMan - wouldn't applying a bonding agent to the patch area also be in order?
I don't know, just asking
 
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Old 01-05-14, 07:08 PM
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bridge may've been my inspector @ 1 time since we prepp'd & repaired 1,000s of ovhd conc reprs in tunnels/parking decks,,, usually we'd outline patch dimensions by 'sounding' [tapping w/16oz hammer - hollow means bad conc], sawcutting the perimeter w/4" grinder & diamond blade, then chipping to sound conc w/15# chipping guns,,, after wetting the conc to surface saturated dry, we'd trowel in ovhd grade polymer-modified repair mortars.

those would suffice for most spall & delamination work,,, occasionally we'd also clean/repair/replace rusted rebar,,, now you know the basics - decent conc repair specialists belong to ICRI.org
 
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Old 01-06-14, 12:15 AM
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marksr--

The prepackaged concrete repair products we used were specified to contain "built-in" bonding agents in the form of powdered polymers, so the only thing needed after sand-blasting and air-drying (with oil-free compressed air) was to baptize the surface with potable water using a mason's brush. It's best for it to be SSD (saturated surface dry), meaning the parent concrete has enough moisture in it to minimize any withdrawal of water from the repair concrete. Bond will be ruined if the repair surface is bone dry, as hydration water at the bond interface will be sucked away into the parent concrete, instead of staying where it will do the most good.

When "pure" concrete containing no additives is used for patch material, then yes, a bonding agent is usually used. Our DOT preference was a neat Portland cement slurry, with the consistency of thick cream, vigorously broomed onto the damp surfaces immediately before the repair concrete was placed.

Troweling in overhead repair mortars as suggested by others is not a good idea for several reasons. Mortar without rock is much weaker than the concrete being repaired, will not perform the same under adverse conditions, and at best is a temporary, band-aid repair. I gave up on mortar repairs early in my 40+ year DOT bridge rehabilitation career for those reasons. Most repair products even in semi-fluid form will obey the laws of gravity, meaning they will naturally tend to pull away from the parent concrete, more so if several layers are applied (in succession) to build up the repair. Each layer adds another potential cold joint and/or bond failure location, increasing the likelihood of early patch failure. That's why the DOTs I worked for always specified solid forms be used to hold overhead patch concrete tightly in place until cured. Coming up with unique solutions to get repair concrete up and inside the forms is where the professionals were separated from the learners in concrete rehabilitation.
 
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Old 01-06-14, 04:47 AM
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yep, agree some repairs are too thick/deep to properly repair in 1 'lift' & that's where experience/knowledge/aptitude/desire are a big help,,, don't recall any 'normal' conc reprs other'n full depth bdge & hgwy (no portland slurries ) but those were done 'right side up' w/suspended form work OR slab-on-grade,,, nevertheless, this thread MAY even help you find the right contractor for the work.

next time we drive thru the holland/lincoln tunnels i'll look to see if troweled patches are still in place - as i recall, they were 10yrs ago but they were only 15yrs old then,,, same w/outerbridge to staten is, geo washington, & tappan zee bdges - good point !
 
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Old 01-07-14, 10:57 AM
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A mortar "Band-Aid" repair can stick and perform only if it isn't subject to internal/external stresses that exceed its cohesive and adhesive attributes (the ability to stick to itself and the parent surface). The OP's situation clearly has such stresses, as indicated by the number of failures he's experienced. The ramifications of applying multiple, thin layers of mortar are clearly visible in some of the pix, appearing as relatively smooth interfaces with little interlocking of aggregate particles. The sporadic air voids and cleavage planes are indicative of gravity working on the mortar while still fluid.

As mentioned previously, any overhead repair has a better chance of adhering if sufficient removal of material surrounding existing rebar is done. I always told my inspectors to use the "grab method," meaning they should be able to put their entire hand/fingers around the perimeter of any exposed rebar, that either has more than half its diameter exposed or is clearly debonded from the parent concrete ("bounces" when struck with a hammer).
 
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Old 01-07-14, 03:47 PM
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your eyes are much better than mine it was rare to apply a ' lift ' thicker than 3" when performing overhead/vertical repairs,,, its good to know aggregate interlock is desired - we rarely did that due to thickness & contract spec'd finishing rqmts per various dot's/engineers/mfg specs

i'd guess ' sporadic air voids and cleavage planes ' indicative poor workmanship over gravity or unsuitable mtls,,, vertical/ovhd repair mortars aren't liquid or weren't in my days,,, IF they were, how would the conc repr tech place the stuff ? ( pre-placed aggregate/pump'd grout exempted )

yes, of course steel should be completely exposed - properly cleaned & coated prior to patch - even replace corroded bar if needed,,, many times rebar expands/exhibits severe rust & causes enlargement thereby cracking/spalling ceilings/floors,,, its generally primary reason for conc failure as above floors/roof is not sealed against wtr / salt intrusion,,, most know conc is porous but few know aci has specs for waterproof conc.

IF we found rust, chipping guns/wire brushes on 4" grinders/sandblasters were tools of choice,,, again, this stuff's all covered in icri specs / guides & is fairly easy for the layman to understand compared to reading engineering specs.
 
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