Uneven slab pour

[Toxictom]

I had a new slab poured in my garage right before winter set in. During the pour, I questioned the finisher why he was hand troweling it and not using a bull float to get a level grade. He assured me it would be level. I did immediately contact the contractor after it set and pointed out how uneven it was with highs and lows all over the place. He has agreed to attempt to get things level by installing a thin layer over the existing slab using concrete glue to help adhesion. I use the garage quite a bit but really don't move a lot of heavy stuff around in it. We only park in the garage during winter. I've told the contractor if it doesn't work he might have to chisel it out and start over. Will another thin layer work and be durable enough, or will it spall and bust apart down the road?

 

[ConCretin]

A thin layer of what? What is this 'concrete glue' you speak of? How was the existing slab surface to be prepped?

Actually, never mind. I can answer your question right now. No, the "thin layer" won't last any longer than it takes your check to clear.

I don't mean to be flippant but you should withhold any outstanding payment and fight this battle now. A skim coat is a hack solution to a hack job. You'd be better off starting over or doing a structural overlay.

For future reference, the general levelness of a slab is determined by the screed. The bull float evens out the local highs/lows and brings the cream up. Float blades (hopefully on a machine) further flattens the floor and steel trowels smooth the surface. It sounds like he skipped one or more of these steps.

 

[larry_g]

Lets not be confusing flat and level. A wall can be flat but out of level by ninety degrees. Level is just that perpendicular with the gravitational pull of the earth. When spec'ing the flatness of the concrete you spec it out in terms of height variation over a given distance. Such as no more than a 1/4" variation in height over any 10' distance. Now you have something specified that you can measure and either pass or fail it per the contract. Then if really on the ball you can also spec grade and slope and probably a few other parameters that you are willing to pay for.

lg
no neat sig line

 

[PCustoms]

Lets not be confusing flat and level. A wall can be flat but out of level by ninety degrees. Level is just that perpendicular with the gravitational pull of the earth.

Let's not be confusing level and plumb...

 

[ConCretin]

I don't think the OP is confused about anything. He just wants advice about how to deal with a wavy i.e not flat concrete slab. Stop me if you've heard this before.

 

[PWC Repair]

Why not just grind it flat and epoxy coat it.

 

[Codyboy]

I had a new slab poured in my garage right before winter set in. During the pour, I questioned the finisher why he was hand troweling it and not using a bull float to get a level grade. He assured me it would be level. I did immediately contact the contractor after it set and pointed out how uneven it was with highs and lows all over the place. He has agreed to attempt to get things level by installing a thin layer over the existing slab using concrete glue to help adhesion. I use the garage quite a bit but really don't move a lot of heavy stuff around in it. We only park in the garage during winter. I've told the contractor if it doesn't work he might have to chisel it out and start over. Will another thin layer work and be durable enough, or will it spall and bust apart down the road?

Highs and lows?

How high and how low?

If you pull a string across it what are we talking about in inches? 1/4", 1/2", an inch?

 

[Toxictom]

Highs and lows?

How high and how low?

If you pull a string across it what are we talking about in inches? 1/4", 1/2", an inch?

Probably 1/4"-3/8" max. I'm clearing everything out of the garage tomorrow. I'll pull a string line in both directions maybe every 12" and mark the lows and highs with chalk.

 

[dcg9381]

Why not just grind it flat and epoxy coat it.

That's like trying to flatten a 4'x8' piece of plywood with a block of sandpaper. Plus it ain't gonna help the low spots.

I've had a few spots "chiseled" out on my slab:

• Front porch was 1" too high
• The forgot the rear "cut out" for the garage door

Not sure what they poured over it, but you could not tell, it has not come off, and it looks like the rest of the concrete.

All concrete has low/high spots. Not sure how bad this is. Garages here are usually "sloped" installs.

 

[Shiftless]

American Concrete institute ACI says that a 3/8 inch variation within any 10 feet is acceptable for a standard slab. ACI 117

 

[PWC Repair]

American Concrete institute ACI says that a 3/8 inch variation within any 10 feet is acceptable for a standard slab. ACI 117

Some residential building code also allows for 1/2" to 3/4" of bow, twist, out of level or square....within 10ft !!!! That doesn't make it acceptable as far as I'm concerned. My shop is 30x48, local concrete guys did the floor for me. There were SEVERAL rain showers before my framing went up. There wasn't any spot puddling water more than 3/16" deep. I told him what I wanted beforehand, he had no issues with that, and got it done.......plain and simple.

 

[PCustoms]

I told him what I wanted beforehand, he had no issues with that, and got it done.......plain and simple.

Seems to be the important part...

 

[jblnut]

I spec’d 1/4” on 20’ in my farm shop with the area in the back being perfectly flat in a 15x30 area. There was a large floor drain in the center to work around and a floor drain in the mech room. He said “that ain’t gonna be cheap” and I said I know. I don’t know what it was extra but the quality that was done was better than I’ve seen anywhere ever before or after. The dude was a ****** to deal with but I knew that going in and it was worth it for the finished product.

He said that had I not given a spec it’d have been between 1/4-1/2” or more variability in 10’ like has been posted above.

 

[Diesel Dan]

Haven't stopped in much over the years and I see things haven't changed much regarding concrete contractors.
For a shop/garage I would not allow a skim coat.

For people looking to get flatwork done, when you start asking about FF/FL #s be prepared for many concrete contractors to walk away. They will verbally say "we will give you a flat floor" but not in writing. What I learned back when I had my 40x72 poured, wide bull float and pans on the power trowel will get you a flatter finish.

 

[PWC Repair]

wide bull float and pans on the power trowel will get you a flatter finish.

That's EXACTLY what my guy did. I remember seeing the pans and thinking..."Why are they putting the power trowels in huge pizza pans??"

 

[Codyboy]

Some residential building code also allows for 1/2" to 3/4" of bow, twist, out of level or square....within 10ft !!!! That doesn't make it acceptable as far as I'm concerned. My shop is 30x48, local concrete guys did the floor for me. There were SEVERAL rain showers before my framing went up. There wasn't any spot puddling water more than 3/16" deep. I told him what I wanted beforehand, he had no issues with that, and got it done.......plain and simple.

I didn't read the links that shiftless posted but I guess 3/8" up and down would net you 3/4" in an area. Not sure if thats right or not.

I do not know or remember exactly how much concrete I had to chip out when I did the 18x18 travertine in our mudroom 20 years ago.
I would say a 3'x4' spot was a 1/2" or more too high. No way to lay tile on it.
I hadto take it down below flat in order to fill it with self leveling floor level.