Problem with unlevel concrete slab.

[Tomcat]

We just had a concrete slab poured for a 40'x28' garage/work shop. The slab has settled out of level. Measuring diagonally across the slab, one corner is 1.5" lower than the highest corner. How serious of a problem is this? Is it to far out of level to build on? Any thoughts or recommendations would be greatly appreciated.

 

[nobull1]

The big question is how much more is it going to settle.What is under it and how long ago was it poured?

 

[DKinWA]

How did you prep the site prior to pouring? Did you pour onto uncompacted fill? Did the slab crack much? Are you sure the forms were set level prior to pouring? What are you using to check level..... laser, water level?

If the prep work was good, you wouldn't typically see changes like this in a short period of time. If the slab isn't showing much in the way of cracking I'd be inclined to check level using another method. It's possible there's some error being introduced in the method of checking.

If the slab is on solid ground and won't settle anymore, you can shim the walls to level everything up. The only issue that comes to mind is controlling water when you park your wet truck in the shop. Obviously water will run to the low side wherever that is and may create problems unless you plan for this. If the slab continues to settle, there is something significant going on underneath that needs to be addressed. Sorry for all the questions, but the additional information helps diagnose the problem.

 

[Tomcat]

Thanks for such a quick response. Some additional information. The slab was poured 7 days ago. The site was prepped with compacted crushed limestone over mostly clay soil. Some soil had to be moved to level the site. The low corner of the slab is where the soil was filled in. I suspect it might not have been compacted enough. I don't know if the forms were absolutely level when the concrete was poured. I'm checking the level with a laser. There is no visible cracking in the slab.

 

[Cliff_Johns]

</font><font color="blue" class="small">( The low corner of the slab is where the soil was filled in. I suspect it might not have been compacted enough. )</font>

Do you really mean filled in soil? I would have though such fill would have been compacted crushed stone or gravel or something like that. Others will know better I'm sure, but that seems wrong to me.

Cliff

 

[beenthere]

In that short of time, I would expect you will see more settling, after some serious cracking. It must be under stress now, and putting a building on it will only load it some more.

If someone else is the contractor responsible for the 'filling' in without compacting, then you have someone to go to to get it fixed before putting a building on it. You will need to decide if you want this project to go further with the risk that is certainly evident.

I would be worried bigtime if it was my slab. I would bite the bullet now, without pouring more money into it by adding a building on top. Now is the easiest time to repair the damage.

 

[DKinWA]

That's a lot of movement for 7 days. To drop 1.5" on a corner there'd have to be some cracking unless the whole slab is moving (very doubtful). Without seeing the site, I'm inclined to believe the forms for the slab weren't completely level prior to pouring.

A slab that's out of level isn't the end of the world, but it does mean a little more work to set the walls. First thing I'd do is get the folks back out that did the work and talk it over with them (also have them shoot grade with their equipment). If I was the contractor and the specs called for a level slab, I'd be in there trying to rectify the problem and make it right. My only real concern would be wether or not the slab is done settling. If it's not going to move anymore, I'd just shim the bottom plate and "git er done"

If I was closer, I'd stop by and take a look. Unfortunately I'd have to drive a bit to get there /forums/images/graemlins/wink.gif

 

[Junkman]

It doesn't matter what the slab was poured over, it wouldn't settle that amount in 7 days without cracking. My guess is that the slab forms weren't set properly and the whole slab is out of level. Did you check the slab for squareness? If it isn't square and it is isn't level, you are going to have one heck of a time putting a building on it. Being out of level will cause some headache if you use horizontal siding, because there is no way to hide the mistake at the bottom, short of planting bushes along the wall. This happened to my foundation when it was originally poured because of a defective transit. It cost a lot of time and energy to correct the problem because the error wasn't found right away. Without seeing the overall conditions, I can't make a recommendation of "live with it, or tear it out". Many times I have read where people want to do part of the work in preparation for a new building, but they don't save money when the project goes wrong and they are the responsible party. When I built my addition my backhoe could have dug the footings, but if anything went wrong, I would be responsible. The contractor dug the footings and when they found that they were out of square, it was his sub contractor that had to come back and correct it. The contractor asked if I wanted to do the additional digging and I declined. There was no way that I wanted to have anything to do with this phase of the construction. If any problem arose in the future, I wanted to have someone else to pay to correct it. Sometimes when you spend more to have it professionally done, you save more in the end by having less aggravation. If you did the digging, filling, and compaction, live with it. If it was done by a contractor, tell him to correct it. If the error is on your part, wait a year and then build after it is finished moving. As a final thought, are you sure that your instrument is correct??????? Set up the laser at each corner and then recheck it.... If you get the same reading 4 times, then it is bad in that corner.... I am hoping for the laser to be off..... cost less to have it re-calibrated than to pour another floor.... /forums/images/graemlins/grin.gif /forums/images/graemlins/blush.gif

 

[Egon]

I also would think the forms were not level.

Egon

 

[David_G]

Don't worry.
The slab for the house next to me was 3.5" out of level but they built the house anyway.
None of the owners have realized. Only because I was here during the building do I know.
The brick layers did a bit of complaining about it.