Garage slab repair

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Old 09-08-19, 11:44 AM
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Garage slab repair

I finally got my garage rubble cleared yesterday. The foundation walls are damaged in a couple of spots and there are several 1' square areas where the slab was eroded by fire. Think divots up to an inch or more deep.

Talking to a contractor who wants the rebuild job and he would just pour a new slab on top of the old. My gut says tear it up and re pour the slab because I don't know what's underneath after all that heat. His way is faster and cheaper so I'm leaning that way.
Anyone know of a good reason not to pour on top of the existing slab or can the damaged slab just be repaired?
 
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09-08-19, 12:21 PM
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I dont think you would "pour a new slab on top of the old" when the original surface could be repaired and simply resurfaced. That's what topping mix is for. But there can be bonding issues, depending on how it's done. Easiest thing to do is to mist the old concrete with water (so the surface isnt dusty and so that it doesn't suck out the moisture from the new concrete too fast) then brush on a slurry of the new mix, (to ensure a good bond) then finish with the topping mix... waiting to steel trowel it until the water has flashed off the surface.
 
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Old 09-08-19, 12:21 PM
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I dont think you would "pour a new slab on top of the old" when the original surface could be repaired and simply resurfaced. That's what topping mix is for. But there can be bonding issues, depending on how it's done. Easiest thing to do is to mist the old concrete with water (so the surface isnt dusty and so that it doesn't suck out the moisture from the new concrete too fast) then brush on a slurry of the new mix, (to ensure a good bond) then finish with the topping mix... waiting to steel trowel it until the water has flashed off the surface.
 
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Old 09-08-19, 05:12 PM
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My neighbor just had his garage floor resurfaced. No fire like yours, but severely pitted. The contractor says up until about two years ago he would not recommend resurface. The stuff flaked off. But new materiel's seem to be better. He still can see the deep pits but the whole floor is smoothed and sealed.

Last year I had mine garage floor epoxied. The contractor used a diamond sander to resurface it then prepped, then applied epoxy, then the decorative flakes and finally a clear coat. 5 days to do it.
 
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Old 09-17-19, 08:44 AM
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I have 3 guys bidding to rebuild the garage. Between them they have 4 or 5 opinions on how to deal with the slab. All were concerned about bonding. The best recommended fix in my mind is to power wash, grind the surface and add a layer of topping mix.

I found a product from Quikrete called bonded topping mix supposedly has bonding agents added to the cement/sand mix. I can't find anywhere to buy it on line.
 
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Old 09-17-19, 09:09 AM
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Those thin top coating materials seem to work ok inside a building but if your in a cold climate with water, salt, freezing temps it will be short lived.

Go to your local cement/concrete store, there are many commercial brands out there which I'm sure is going to be better than anything available at big box store!
 
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Old 10-05-19, 05:29 AM
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The garage foundation has developed several cracks that were not there before or several days after the fire. I think they showed up as the foundation walls cooled. Again, I talked to 3 different guys and they all have differing opinions on how to fix the cracks. Everything from cutting the crack out, adding rebar and repouring that section to injecting an epoxy into the crack. One guy said that he would simply strap across the crack so that it couldn't expand.

There are 2 cracks about 1/8" wide and a half dozen hairline cracks. I want to get them fixed before freezing weather sets in. What's the best fix to keep the cracks from spreading?
 
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Old 10-05-19, 05:33 AM
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Never hears of the strapping idea. The best, but most expensive is the re pour. The epoxy thing sounds reasonable. can he give you any kind of warranty and if it fails what can be done to fix it again?
 
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Old 10-10-19, 10:56 AM
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I had the last contractor do a work up on the house and garage today. His opinion is that the entire garage foundation, slab and walls, needs to be replaced because of the fire damage. He said the slab expands from the heat of the fire and usually causes structural damage to the foundation walls below grade.

This guy has a good rep in my area but I don't know if he's blowing smoke. Any concrete guys with an opinion?
 
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Old 10-10-19, 01:34 PM
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I don't profess to be a concrete guy, although I've done my fair share of it, and I'd agree with him. You said it yourself in your first post... listen to what your gut is telling you. Insurance ought to pay for replacement if you had fire insurance.
 
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Old 10-10-19, 02:22 PM
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Part of the problem is that I'm getting differing opinions. I'll probably end up getting an engineer to look at it.

I had insurance coverage but only for roughly what the garage cost me to build ($25K) 12 years ago. I built it myself except for the foundation. It was two story with a 400 s/f workshop over a 2 bay garage.

I don't think the coverage I have pay would be enough to replace it so I'm planning on downsizing - single story no shop and I would do all the electric/GDOs/sheetrock myself. Even downsized the cost of a new foundation would probably eat up a large part of the $29K payout from the insurance guys.
 
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