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tribander 04-15-2009 02:00 PM

Replacing Concrete Garage Slab
My wood frame garage (22' X 24') and the concrete slab it sits on are 35 years old. The garage is in excellent condition is solid and square. (I built it myself). The problem is the slab (Wisconsin winters). It has some wide cracks and has risen up in the middle so the bottom of the garage door cannot sit flat on the slab. Everywhere along the outside perimeter the concrete is flat and the bottom plate is straight and is in good condition.

In the past week I've had six contractors give me estimates on replacing the slab. Two of them say the only proper way to replace the slab is to jack-up the garage and completely pull out all the original concrete. The other four say that because the building is solid and square that cutting the slab about 12" - 18" away from the plate and leaving the original 8" thick concrete under the slab should work fine.

Of course they will drill holes in the old and use rebars to tie the old and new concrete together. They claim after 35 years of settling all settling should be over by now.

The difference in cost between jacking the building up and cutting around the interior of the slab is substantial as you can imagine: in the neighborhood of $2,000. I can think of a lot of other things to do with $2,000 if the results are going to be close to the same. Don't get me wrong though I do want it done right. In addition, some of these experts claim that jacking-up the garage could cause it more harm than good and to complicate things even more, there is a 2 foot square cinderblock chimmney sitting on the slab!

By-the-way, I am sixty years old and plan on remaining in this house for the foreseeable future. Thanks for any and all help!

kok328 04-15-2009 04:50 PM

I'm no expert but, it seems that saw cutting the perimeter would be the best way to proceed. Are they proposing expansion joints between the old and new?

tribander 04-15-2009 06:15 PM


Originally Posted by kok328 (Post 29538)
I'm no expert but, it seems that saw cutting the perimeter would be the best way to proceed. Are they proposing expansion joints between the old and new?

Thanks so much for your input. None of the contractors who recommend sawing the concrete said they would use an expansion joint between the old and the new. Only that they will use 5/8" rebar epoxied into the remaining concrete the plate is resting on and bringing the new concrete right up to the old.

Maybe it would be better with an expansion joint? What do you think?

kok328 04-16-2009 06:45 AM

If that is the direction you go, I would think that what the contractors says would be best, otherwise you'll end up with a floating block for a garage floor. Over time it may settle and create a trip hazard and become uneven and then you'll be right be where you started.

yesitsconcrete 04-20-2009 04:21 AM

wow, hey guys - jack THIS ! ! !

sounds like some expansive soils which i have in my garage,,, w/o replacing that nothing'll work - use a coarse aggregate washed sand mix - nysdot item #4, gadot gabc - in wisc, i'd use horizontal tie bars however its more important to have a proper jnt pattern - mine doesn't/didn/t :mad: but those guys got paid & they're gone,,, if it were mine, i'd just repair the heav'd section but i AM an expert :rolleyes: even if my own mind,,, good luck ! ! !

ps - my neighbor's so cheap he'd notch his door :eek: {66 & only leavin' when i assume room temp }

tribander 04-21-2009 09:22 AM

I like your quote: "but those guys got paid & they're gone,,,", that's really the bottom line here and that's why I'm having a difficult time making up my mind what to do.

The way some of these guys (experts) are wondering how they'll jack-up the garage would make a great comedy movie after the likes of Laurel & Hardy.

Your take on the soil is right-on, EVERYONE's concrete in this neighborhood has heaved and broken concrete at one time or another. All clay and in the winter it expands like crazy. One section of side-walk going to my house door rises up 1.5" to 2" during the winter and settles back down to 0" in the spring.

Thanks for your input and advice. Oh, by the way, I'm not quite as cheap as your neighbor, I thought about notching the door but rented a grinder instead and took out my frustration on the concrete. It truly looks like hell but it did help some.

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