How flat should a newly poured shop floor slab be?

I had a 1000 sq ft slab poured recently for an addition to my shop. It rained a few days later. As the slab dried off from the rain a "bird bath" puddle about 15' in diameter and 5/8" at the deepest point became apparent.

Is a 5/8" deep puddle considered reasonable/expected or should I expect the slab to be flatter?

Thank you, Bruce

5/8" is huge. I would find that totally unacceptable on a 1000 sq. ft slab.

Bruce, it can happen for various reasons, but I worked on a crew yrs. ago pouring slabs for buildings that size or larger, and it would not have been acceptable to us.
James

Well the die is cast as they say. Unexceptionable or not, what are your options? Pretty much nothing. Mark it and work around it if you can.

Tom

If 5/8" is not acceptable what are my options? At one extream I could demand the contractor cut it out and repour. But is that resonable on my part?

The contractor hasn't been real responsive when I bring it up. He has said the cement guy would look at it but as far as I know this hasn't happened.

I don't want to be a jerk about it but I don't want to be taken advantage of either.

In the mean time, the shop walls and roof have gone up.

I don't know what remedies you have available, especially if this floor is supposed to carry a substantial load.

For comparison, 5/8" in 7.5' is about 0.7% grade. Sidewalks are deliberately tilted 2% grade for effective water drainage. So this is a pretty noticeable dip.

If you didn't specify flatness, and obligate a remedy, then.....

Permit?

Did you pull a permit?

Did you have a blueprint?

Is the provider licensed and insured?

If any anser is no then you may be out of luck.

But if you have a permit, then the inspector can help, if you are not happy then they can "red tag" it.

Hard to get a permit without any blueprints or engineering, but the blueprint should have stated how the concrete was to be done.

If licensed, insured and permited with a red tag, then insurance company may remidy.

Repour...maybe not, after cure a thin set epoxy based top pour may be applied over the top that is just a strong as the concrest and can be made real flat and level, this is best to seek advise of those who do that for a living.

Any building engineers here?

in my experience if the pond is in the middle of the floor, it will only get worse over time.

i would be having a fit!

only one way i would put up with a slanted floor and that is so that it could drain toward a floor or out a door, either of course by design.

its going to be a lot easier to remedy now than if you wait for the concrete to fully cure.

bob g

btw, i bet they added water to the mix to make it easier to work, this does another couple of things, it increases the slump, allows for more shrinkage on setting, and reduces strength.

all of which lead to this sort of problem and more over time, so yes i would explore all options on getting this redone.

bob g

Just some thoughts, all of which can have an effect.

How thick is this slab?

What if any reinforcing?

How was the reinforcing set,...... in mid slab or just left on the bottom etc etc etc?

What's under the slab in the way of subsoil, hardcore / foundations etc etc.

What was the mix and slump spec?

And possibly the most telling, was the job done to a price (hint low / ''negotiated down'') or a firm spec.

Like stated above.

1. That much deflection is unacceptable
2. W/o a set of specs in contract, any "industry specs" debate would go on and on.
3. There is a product called Ardex(sp) we use to bring concrete slabs up to flatness spec for further finishings ( finish flooring, special coatings, etc). 5/8" is probably on the extreme edge of application (depth). And, you'll find these "dips are usually an irregularly shaped area. Makes cutting and patching more of a challenge. But this may be your option.

IIRC a lot of slabs we do have a 1/4" in 10 deflection spec.

when they poured a slab in my barn, it drops (lengthwise) 3" in 7 feet (14*24 &14*48) of course rises back up the other side
& lacks fiber which i paid for
wasn't permitted as permits not required where i are
immediately following that their phone # disconnected
plates, screws and blocks

BruceC said:

I had a 1000 sq ft slab poured recently for an addition to my shop. It rained a few days later. As the slab dried off from the rain a "bird bath" puddle about 15' in diameter and 5/8" at the deepest point became apparent.

Is a 5/8" deep puddle considered reasonable/expected or should I expect the slab to be flatter?

Thank you, Bruce

Click to expand...

Sorry to hear this, Bruce. Your shop floor should, at a minimum, meet the specs for a class C floor, which, in the old days, was 1/4" in a 10' straightedge. If you haven't paid, I wouldn't. If you have paid it probably isn't worth the hassle to try to get the contractor to fix it. Due to the economy, most of these guys are barely getting by, so they won't have any money to go after. The best remedy is probably an epoxy overlay, as previously mentioned.
Jim

I had a friend who had a 6" thick shop floor poured with a real tight spec of 1/8" in 10'. The contractor didn't meet it the first go around and ended up cutting the slab in squares and lifting them out with a crane since the block walls of the shop were already up. Need to have the spec in writing.

Thanks everyone for taking the time to give your input. A number of you asked questions. Here are some answers:

The shop was drawn up by a company called D and Z Designs. I initially assumed it was an architectural firm but later found out, like the name suggests, they are a design firm which may be consistent with me needing to get a structural engineer to sign off on the plans.

I got permits from the City and after considering 4 bids for the foundation, framing, and roof picked the cheapest one which happened to also be the company which constructed the initial shop. The contactor is licensed by the state of CA, and thus, insured. (According to my understanding.)

I don't understand what "red tag" is and how the inspector and insurance company can be helpful.

The slab is 5" thick with 5" of base rock, 2" of sand and a 10 mil vapor barrier. #3 rebar, 18" OC raised up on (approx) 2" cement blocks. I don't know what the mix and slump specs are. The shape of the foundation is 5 sided all sides being of different length. (To fit in the back corner of the lot.) I asked the designer if there are any "flatness" specs for the slab on the plans and he responded no.

(Just in case you are interested: The walls are 8" tall constructed with 2x6's, the ceiling slopes up to a flat of 9' with a roof pitch of 2.5/12. (Because of city set back this part of the shop can't be over 12' high.))

The way the contract is set up I pay every 15 days for what % of the job has been finished. So I have not paid for the whole job yet.

I found out this morning the cement person did come by yesterday and to look at the job issue but have not heard his comments. I will bring up using "leveling" products (ex, Ardex) to repair the slab surface as one option.

It didn't occure to me I needed to define "flat" in the contract. I'll know better next time.

It seems most suggest the "bird bath" is outside the confines of quality work and that my options are (1) add some kind of leveling surface, (2) cut out the area of the puddle, (3) ask for a decrease in the cost.

Any other suggestions?

Thank you, Bruce

To be honest, my 300sft floor has dips that are that bad, but I didn't pay myself when I laid it, so I'm not going to sue me either

I would suggest that screeding the floor level may lead to problems later if the movement of loads across the surface cause the layers to separate. Look into the possibility of getting the floor ground level.

Probably won't make you feel any better but there is a very large building in a city near me that has the second floor poured 2" out of level! AND it was set up with lasers! It drove the other trades crews nuts having to compensate for it.
Will this really affect your usage of the building? Besides just pissing you off at their poor finishing skills every time you think about it?

I am not sure if the uneven floor will make a difference in the long run. But, if I don't make an issue of it now I think it will be difficult to hold the contractor accountable later. Do I make an issue of it now or give up that right and risk discovering problems later. I don't know the answer.

Can the floor be ground flat? How dose one do this? This option was mentioned in a previous post.

BruceC said:

I am not sure if the uneven floor will make a difference in the long run. But, if I don't make an issue of it now I think it will be difficult to hold the contractor accountable later. Do I make an issue of it now or give up that right and risk discovering problems later. I don't know the answer.

Can the floor be ground flat? How dose one do this? This option was mentioned in a previous post.

Click to expand...

Trying to remove 5/8" from the rest of the floor is going to cost a fortune. If it were my shop, I'd have the low area removed and re-poured. The perimeter of the area should be sawcut, obviously. You don't need a written spec for a job this poorly done. They are required to do what the law calls "a workmanlike job." That means, for a typical concrete slab, you can't complain about 1/4", but 5/8" is way outside what could reasonably be expected from a professional contractor.
If you are acting as your own general contractor...hiring your subcontractors yourself....you should talk to the concrete guy. If you have hired a general contractor, who is responsible for hiring the subs, you should talk to him....not the concrete sub.
Do NOT pay for the slab! That's the only leverage you have. Get a written acknowledgement of the problem, and agreement to fix the problem before paying any money.
Jim