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Discussion Starter · #1 ·
We walk into some horrendous floor prep jobs, this one is more of a concrete trade maybe.
Approx 1000 sq ft. open area inside a building, kinda round shape with doors about 15 doors around perimeter. They are all about 4" higher than the slab with concrete ramps about two foot long. I don't know how they got away with this but so it goes.
So I get there, I got a little heads up to see what equipment I will need to bring, there's some rough areas of concrete and rebar sticking through in spots where they removed walls etc. also carpet adhesive layers built up about 3/16" thick.
Now by the time "flooring installers/contractors " such as myself come in, the site needs some cleaning up and the floor " covered"
The exterior double doors are in, but it looks to me that a slab 4" thick needs to be poured on top of existing slab to height of all doorways, exterior doors set to this height and take care of the pitch on the outside of the building.
When pouring a slab on top of another one is this acceptable? How do you tie it in to existing slab? I can remove adhesive and scarify if necessary. Should it all be doweled and rebar into existing slab or should the whole thing be cut out, removed, 4" of fill dirt and repoured?
I've often wondered this process for other buildings as well. Please respond!
 

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I have helped on a few jobs before where we poured over an existing slab, I am not sure if it is acceptable or not, but they did it anyway.

Two things come to mind. If the existing slab is heaving or excessively cracked or showing other signs of poor sub grade then it probably won't work out well. The other is to put some sort of barrier between the two slabs. Plain old clear poly will work. I was told it was to prevent any existing cracks from showing through.

Again, these weren't my jobs, but the guys doing them had done it that way before and not had a call back, so use discretion I guess and talk to the building inspector to make sure they won't raise a stink about it.
 

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Discussion Starter · #3 ·
Thanks, not sure what they want to do , it could have been handled already, interesting how they isolated it versus tie it together.
 

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Discussion Starter · #4 ·
We 're delayed and haven't shown up yet, what I should have said the slab should have been poured already to match height of doors.
I didn't realize concrete contractors can't read, so how can they give advice, that's probably why I only had one response, oh well.
 

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I've seen slab on slab poured and bonded together and with an isolation membrane. Just depends on what the archy/Engineer intended or wanted to accomplish.
 

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We just had a 2nd story addition where the existing slab, that is over 50 years old, turned out to have been a two pour slab with some sort of tar paper between the two. The slab looked fine and nobody had any idea it was like this until the slab was cut for the 2nd story footings. We ended up having the whole slab removed because of concerns of attaching the new footings to the existing slab but the original had held up fine for all of those years.

This house was part of a tract and the best guess it the developer was trying a new system of slab on grade construction, maybe was worried about moisture coming up through the slab?

Just saw that the photos didn't upload, I think the file's too big but the two slabs were about 4" on the bottom and 2-1/2-3" on the top with paper or felt in between.
 

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I didn't realize concrete contractors can't read, so how can they give advice, that's probably why I only had one response, oh well.
Insulting an entire trade probably isn't the best way to get help. :blink:

I've seen slabs poured on other slabs with dowels, some have used a product called WeldCrete, and others have been isolated. Alot depends on thickness of new slab.

I think all three methods work in different situations. Hard to say without seeing it.
 

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Discussion Starter · #9 ·
Cool, I know on site makes a world of difference, appreciate all the advice, I was just playin, no one realizes how hard all these construction trades work. I've done a bit of it and it sure isn't "user friendly"
I guess busting it all out would be the costliest, but proper way, would hate to have to get to a pipe under 8" slab.
I try to go to World of Concrete, the flooring trade goes hand in hand, and yeah, even brick/block layers are the same " family"
 

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As previously stated, the first thing to look at would be the integrity of the existing slab. Cracks would be one thing to look at. Another is heaving or sunken areas. If any heaving or sinking has occurred, then the concrete must be removed. If its just cracking, depending on the severity, an isolation barrier could be placed over the existing slab, such as poly or felt paper. Rebar reinforcing should be used to help insure the fault cracks will not transfer into new concrete. Also, all rebar would need to be cut off and all existing walls demoed to the existing level. And, I'm sure the ramps leading to the doors would need to be removed as well. I have never been a fan of bonding to an existing slab when over pouring.
 

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Approx 1000 sq ft. open area inside a building, kinda round shape with doors about 15 doors around perimeter. They are all about 4" higher than the slab with concrete ramps about two foot long. I don't know how they got away with this but so it goes.
I am curious. 1000 sq ft. Round shape. 15 doors. Sunken slab.

Grain Bin?
Missile Silo?
Lighthouse?

Need pics. :laughing:
 

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Discussion Starter · #12 ·
A lobby of a church, I have the # of a local concrete contractor, been wanting to pick his brain anyway , one of the wife's relatives.
Currently the slab has a lot of adhesive , it doesn't look to be dropped from cracks , and heaving as far as I know in central Florida I haven't heard of , I've seen it in Arizona.
I Agree about busting out the ramps if filled, it just seemed to be the answer prior to putting in the Double entry front and back doors.
Thanks for the assistance.
 

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Discussion Starter · #14 ·
I'd be Leary to do that due to compressing of the foam. Here concrete is almost always cracked, the control joints are usually 1/16" gap.
 

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I would probably pour over it. Since you are going 4" you should be fine. If it were mine, I would definately lay-in 6x6 mesh or 2' x 2' - 1/2" rebar grid. As far as cracks go, I would try to cut my control joints close to the existing cracks. As long as it is inside a foundation, as opposed to a floating slab, you shouldn't have any problem.

If you were thinking about pouring 2" over existing that would be different. I think 4" will be fine.
 

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Discussion Starter · #16 ·
Yes, I wouldn't trust 2" thick unless it were specially mixed somehow. How easy life would be if the top one inch were poured like water to be flat as could be. We may go there today to go over with builder.
 

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Pump able floor leveller material, we use a product called Agillia Screed A from Lafarge. I'm sure you have something the same, possibly a different name. We pour it to an average thickness of 2", can be a little thicker if needed, doesn't level too well under 1", need another product for that call Fina. Floor must be clean and primed with a product from Mapie call Primer L.

The product is delivered to site on ready mix trucks, has a truck life of 4 hours, so you have lots of time to work with it. It will cure out around double the strength you order.
 

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Discussion Starter · #18 ·
Couple inches of rain today, went by to look at it , the back door pitched in so they'll have to redirect exterior.
I asked builder, he said they didn't want to raise it 4" and it being a church he said they were exempt from ADA, as it was existing.

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