Cracked and sunken slab (pics)

[BJR]

Ah the 50s - before they bothered to compact the soil after backfilling. My attached garage had a cracked and sunken slab but I knew the only way to fix it was to tear out and start over. To my surprise, even though the slab sunk 8.5", was the voids underneath were easily that much. This work took place between Christmas and New Years this year. I have a concrete recycling place not too far and hauled about 25k lb of concrete in my truck.

I left the slab by the stairs to make the new pour easier. Cut with a diamond blade in a circ saw - discovered the slab was completely floating but supported on three sides.

 

[BJR]

...and the new slab. It's pinned to the existing structure and wire meshed. No cracks, yet, and the finishers did a spectacular job.

After much research on GJ I put in vapor barrier, insulation and radiant floor tubes.

Edit: This pour was in Feb - I was up all night like a new dad and watered for the next three days.

 

[MadMechMaster]

Wow! That was an extreme case. Nice post, I'm glad you got it straightend out.

 

[M17715]

Yes, that's a lot of work. Congrats on the job!!

 

[Ric in Richmond]

I have a cracked 1950's garage floor. Drives me nuts but not in the budget. Yours will make me think twice!!

Glad you never bolted a lift to that.....

 

[BJR]

I have a cracked 1950's garage floor. Drives me nuts but not in the budget. Yours will make me think twice!!

Glad you never bolted a lift to that.....

There was also a 4" void under the door so it never sealed. So frustrating!

I always wondered if it failed catastrophically or gradually...could you imagine being in a call and *boom* it suddenly drops 8"?

 

[theoldwizard1]

...and the new slab. It's pinned to the existing structure and wire meshed. No cracks, yet, and the finishers did a spectacular job.

After much research on GJ I put in vapor barrier, insulation and radiant floor tubes.

Edit: This pour was in Feb - I was up all night like a new dad and watered for the next three days.

When I was knee high to a grasshopper, we had a slab poured for a garage. I remember my Dad watering for about a week ! No one seems to do that anymore.

 

[Big-Foot]

Wow that was pretty extreme.. Almost sinkhole-ish underneath!
I will remember this post the next time I am whining about a couple of cracks in my cement..

When I was knee high to a grasshopper, we had a slab poured for a garage. I remember my Dad watering for about a week ! No one seems to do that anymore.

I am HUGE on watering daily to promote the more solid cure...

Most people don't know that concrete carries it's own oxygen/air and they look at you like you were from outerspace when they see you sprinkling the fresh concrete!

 

[Spudland_Dave]

Wow that was pretty extreme.. Almost sinkhole-ish underneath!
I will remember this post the next time I am whining about a couple of cracks in my cement..


I am HUGE on watering daily to promote the more solid cure...

Most people don't know that concrete carries it's own oxygen/air and they look at you like you were from outerspace when they see you sprinkling the fresh concrete!

You may want to read up on modern day concrete. Being from the old school..many people told me the same thing, after we poured my slab between hits with the float I chatted with my concrete guy, he said with modern day chemicals and additives in the 'crete, there is NO need for that, if anything it could HURT the finish. On hot summer days the relatively cool water hitting the very hot slab causes the top to "shock" and it could develop hairline cracks all over which can pop off down the road. Todays concrete is nothing like it used to be...they can add all sorts of additives to do all kinds of things. Its not just Cement, Water & Aggregate anymore.

So I listened to my guy, didn't put a drop of water on it, and my slab is absolutely beautiful. I've actually gotten a lot of compliments on it.

 

[Jagmandave]

My house was built in '64, and about 1996 I tore out the 20X20 patio and replaced it - that was some of the hardest, toughest, meanest concrete to bust up I've ever encountered. My concrete supplier said "yep, they don't make it like that anymore"

I need to do my driveway and garage slab, but I cannot DIY anymore so I'm dreading what that might cost! A couple of years ago I had the drive mud jacked as it had dropped 8" right in front of the garage door, and so far that's held up well, but the garage floor has cracked and raised or dropped in places as much as 1/2 inch or more.

It's pretty impossible to run a floor jack on it, the crack is always right where you want to lift!

 

[Highbeam]

I watered my slab for a week. The "new" concrete is still water, cement, sand, and rock. They CAN add other stuff to improve various qualities but in all cases, hydration makes the concrete stronger. More importantly, you water so that the concrete cures evenly. You don't want the top to dry out and stop curing while the bottom is still cooking, that differential could cause deep cracks.

Concrete continues to gain strength so long as moisture is present. Concrete drying out is a bad thing.

 

[Kevin54]

Do you know what caused it in the first place? And looking at the pic, it looks like there is more than just the slab, as it looks like both walls are cracked as well.

 

[musgofasta]

Did you do all of that with just a jack-hammer? Good grief, how does your body feel?

 

[theoldwizard1]

Did you do all of that with just a jack-hammer? Good grief, how does your body feel?

Forget the jack hammer ! Someone had to haul all those pieces out to the truck !

 

[BJR]

Do you know what caused it in the first place? And looking at the pic, it looks like there is more than just the slab, as it looks like both walls are cracked as well.

Some of the blocks are cracked, yes. There was a downspout that was essentially dumping water at one of the corners and I'm sure that contributed to the issues.

Forget the jack hammer ! Someone had to haul all those pieces out to the truck !

Yep, I hauled all of it to a local concrete recycling center in my pickup and had to unload it by hand, as well.

 

[PAToyota]

Ah the 50s - before they bothered to compact the soil after backfilling.

Unfortunately, you'll still find a lot of contractors who will run the skidloader over it a few times and say that reinforcing in slabs is a waste of money because "that's the way they always do it..."

 

[BJR]

Unfortunately, you'll still find a lot of contractors who will run the skidloader over it a few times and say that reinforcing in slabs is a waste of money because "that's the way they always do it..."

Hey, you may remember my creative ceiling correction on PBB:


Redoing the joists is still on the list.