Concrete slab on slab question

[Rommel]

My house is located West of St. Louis in a subdivision with basements. I have a 3 car garage with the left and right bays being 26 feet deep but the middle bay is only 20 feet deep because my laundry/mud room is there. Laundry is not over a basement, it is on a slab in the garage area and higher than the garage floor. Laundry room is original construction, house built in 2006. No plumbing in floor, goes through shared interior wall to basement. I can see some separation between the laundry slab and garage floor slab and can slide a piece of paper about 6+ inches under my laundry room at some points. I'm not worried about the separation.

I would like to expand my garage by getting rid of my laundry room (move to basement, not looking for opinions on why main floor laundry is best). I would like to know what to expect when I get rid of the laundry room slab. Is anyone familiar with how these are poured? I doubt I'd have a continuous garage floor underneath this, though it'd be ideal. If I do, would there be rebar tying the two slabs together? I've seen some front porches that have a perimeter short wall foundation filled with rock and a slab poured on top and would not be surprised if this is done the same way; but 6+ inches seems like a lot for the slab to overhang the footing. Anyone here pour concrete in cookie cutter homes in the Midwest and have input on this common practice?

I have just started moving all the non car stuff out of the garage. Just built a 10x12 shed for yard and pool stuff and setup a workshop in unfinished part of basement for home repair tools/materials.

Few photos of what I'm starting with:

 

[Uncle murph]

My house is located West of St. Louis in a subdivision with basements. I have a 3 car garage with the left and right bays being 26 feet deep but the middle bay is only 20 feet deep because my laundry/mud room is there. Laundry is not over a basement, it is on a slab in the garage area and higher than the garage floor. Laundry room is original construction, house built in 2006. No plumbing in floor, goes through shared interior wall to basement. I can see some separation between the laundry slab and garage floor slab and can slide a piece of paper about 6+ inches under my laundry room at some points. I'm not worried about the separation.

I would like to expand my garage by getting rid of my laundry room (move to basement, not looking for opinions on why main floor laundry is best). I would like to know what to expect when I get rid of the laundry room slab. Is anyone familiar with how these are poured? I doubt I'd have a continuous garage floor underneath this, though it'd be ideal. If I do, would there be rebar tying the two slabs together? I've seen some front porches that have a perimeter short wall foundation filled with rock and a slab poured on top and would not be surprised if this is done the same way; but 6+ inches seems like a lot for the slab to overhang the footing. Anyone here pour concrete in cookie cutter homes in the Midwest and have input on this common practice?

I have just started moving all the non car stuff out of the garage. Just built a 10x12 shed for yard and pool stuff and setup a workshop in unfinished part of basement for home repair tools/materials.

Few photos of what I'm starting with:

20-1 it’s sitting on a continuous finished slab.

 

[Ricky Joe]

Hit that with a hammer. Looks to me like cinder block with a skim coat, not poured concrete to a form.

 

[allinon72]

Weird that it looks like an afterthought, perhaps that’s an option your builder offered, with an alternative location elsewhere?

In any event, seems like a good bet that it’s a few courses of block, 4-6” of rock inside that with the slab poured over the top. There’s no logical reason why the main slab wouldn’t be present under that area. Is there a place in the laundry room where you could make an exploratory hole?

 

[CraigStu]

Just in case it turns out to be a slab on a slab would it be too terrible to tear out the walls and leave that slab?

 

[Chaznsc]

Drill a hole to the depth of the UR slab, plus an inch, then see if there is soil or concrete in the next layer.

 

[MWitte]

I think most decisions made in construction of a house to sell are based on what is quick and easy for the builders. I think there is a pretty good chance there is a flat floor there at garage floor level. It would have been quick & easy for them to form & pour the laundry room floor on top of that.

 

[Zeke]

Plumbing goes through which wall? The shared wall with the house? Does that not tell you where the basement walls are?
I'm with the rest that the area below the existing laundry is slab on grade.

What a lot of work. Reminds me of when I was younger and full of energy but not a much brain power. I once thought about digging a basement a 5 gallon bucket at a time. It's been done on Youtube many times but it takes like a year part time.

 

[NUTTSGT]

Drill a hole to the depth of the UR slab, plus an inch, then see if there is soil or concrete in the next layer.

Definitely quick and easy way to figure out what is under the slab

I think most decisions made in construction of a house to sell are based on what is quick and easy for the builders. I think there is a pretty good chance there is a flat floor there at garage floor level. It would have been quick & easy for them to form & pour the laundry room floor on top of that.

I'd agree.

Losing several feet of garage space for a utility room isn't an odd thought for some home buyers that would rather have a first floor laundry.



I'd probably cut it in 1-2' squares and try to break out in chunks rather than little -little pieces.

 

[wssix99]

20-1 it’s sitting on a continuous finished slab.

Yes, that's what i looks like. If it was any other way, there would be reentrant cracks on the base slab and I don't see those.

I would start the demo by having my wife lift the room slab with a very large pry bar (protecting the base slab with a wood block) and then have her swing a sledge hammer to break it up.

 

[Rommel]

Hit that with a hammer. Looks to me like cinder block with a skim coat, not poured concrete to a form.

There's a chunk missing at the top of the slab where the bottom wall plate sits, appears to be poured concrete. I think they did skim coat it just to cover the ugly from the forms.

Weird that it looks like an afterthought, perhaps that’s an option your builder offered, with an alternative location elsewhere?

In any event, seems like a good bet that it’s a few courses of block, 4-6” of rock inside that with the slab poured over the top. There’s no logical reason why the main slab wouldn’t be present under that area. Is there a place in the laundry room where you could make an exploratory hole?

Standard location on this model home with both 2 and 3 car garages.

Just in case it turns out to be a slab on a slab would it be too terrible to tear out the walls and leave that slab?

I'd like it gone. I don't mind doing the work, willing to cut/jackhammer and pour some concrete if I have to, just hoping to know before I start what I have ahead.

Drill a hole to the depth of the UR slab, plus an inch, then see if there is soil or concrete in the next layer.

Probably do that in the next couple days.

I think most decisions made in construction of a house to sell are based on what is quick and easy for the builders. I think there is a pretty good chance there is a flat floor there at garage floor level. It would have been quick & easy for them to form & pour the laundry room floor on top of that.

That's what I was hoping, but not wasn't exactly sure what to expect.

Plumbing goes through which wall? The shared wall with the house? Does that not tell you where the basement walls are?
I'm with the rest that the area below the existing laundry is slab on grade.

What a lot of work. Reminds me of when I was younger and full of energy but not a much brain power. I once thought about digging a basement a 5 gallon bucket at a time. It's been done on Youtube many times but it takes like a year part time.

There's no question about where the basement walls are, that's not what this is about. There is only one shared interior wall as shown by my diagram. My only reason for mentioning this is so I didn't get replies saying there could be plumbing in my slab. Was simply looking to see if it was common to find finished concrete underneath something like this or not.



Thanks for all the replies.

 

[Zeke]

Then it's drill or core. I wouldn't have wasted the slab concrete to go all the way to the shared wall. I wouldn't have out a slab over a slab either, but I can see the short cut. I would have formed the laundry and poured it all at once. But the crack says that didn't happen.

Good luck, you might be excavating and placing more concrete at the garage floor grade. Not the worst job I've done.