Building Performance Knowledge Community

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When you tell your client, "Although the slab doesn't meet the specifications for levelness, it is OK - we should accept the slab.", then there's a problem somewhere.

I am trying to get a handle on this "F" method for assessing the flatness and levelness of a slab. My structural engineer specified flatness of 25 overall and 20 local and the levelness at 17 overall and 13 local. I understand that this is not particularly stringent. The building does not require any special attention to flatness/levelness (F/L) as a response to its utilization and function. The specification did not address any monetary penalties as a remedy for failure to meet the specification, and the reality is that the failure to meet the levelness factor does not create any problem for the building use, nor the aesthetics of the building. The finished floor is to be sealed concrete, so any "repairs" would likely create a negative impact aesthetically.

How do you deal with this?
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Steven Cox AIA
President
Cox Architecture
Mccomb MS
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I only see one potential problem with accepting a slab that is adequate for the purpose it serves but that does not meet an overly-strict specification: If the project was competitively bid, it's difficult to know whether or not the contractors who did not win the bid were handicapped by the assumption that the slab would be rejected if it didn't meet the specifications. If the bid forms make it appear as if that is the case, it would be irresponsible not to ask the contractor how he or she proposes to correct the inequity. However, it's possible that this contractor's primary advantage on bid day was the knowledge that the slab was over-specified, so it puts the owner and the architect in a difficult spot. Once that spec is on the street and not corrected via addendum, it's almost impossible to later correct the problem without creating an unfair "gotcha". I would put this in the category of "lessons learned."

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Sean Catherall AIA
Integrated Property Services
Herriman UT
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You can search the Internet for "concrete flatness and levelness" to get a quick update on this system of flatness (how bumpy the slab is) and levelness (how much the slab slopes.)

You did not mention how the slab differs from the specified tolerances.  However, a flatness of 25 is roughly equivalent to 1/4" in 10 feet, which is a pretty loose tolerance.  I would not think this amounts to much over-specification of flatness, though it does require more care than a simple bull-float finish.  The key factor here is that the contractor failed to provide the quality of work specified, irrespective of whether or not that tolerance was necessary for the project.  If the Owner is willing to accept the work as is, an equitable solution may be for the Contractor to offer financial compensation - based on how far he missed the spec - for his lack of performance. 

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David Schele AIA
Felder Group Architects Inc
Austin TX
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Original Message:
Sent: 03-11-2013 18:35
From: Sean Catherall
Subject: Concrete Flatness / Levelness ASTM E 1122-87

I only see one potential problem with accepting a slab that is adequate for the purpose it serves but that does not meet an overly-strict specification: If the project was competitively bid, it's difficult to know whether or not the contractors who did not win the bid were handicapped by the assumption that the slab would be rejected if it didn't meet the specifications. If the bid forms make it appear as if that is the case, it would be irresponsible not to ask the contractor how he or she proposes to correct the inequity. However, it's possible that this contractor's primary advantage on bid day was the knowledge that the slab was over-specified, so it puts the owner and the architect in a difficult spot. Once that spec is on the street and not corrected via addendum, it's almost impossible to later correct the problem without creating an unfair "gotcha". I would put this in the category of "lessons learned."

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Sean Catherall AIA
Integrated Property Services
Herriman UT
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Sean's scenario is remedied by officially recording the non-compliance with the contract... then being the 'neutral' (as the contract contemplates, if using standard AIA contracts) attempting to ensure conformance by both parties to the contract by sitting down with the Owner and Contractor and discussing a reasonable credit back for the reduced value of the sub-spec slab.  You may need to consult an objective third party to obtain a reasonable value reduction as a target for the discussion.  Clearly, if the slab 'performs' and this is really only an academic issue, the reasonable reduction in value is not going to be a significant number - but it will surely be less than the cost of mitigation.

The larger question to be asked, in terms of practice, is:  if the slab surface is not critical, and the sub-spec floor is actually OK in terms of both utility and aesthetics...  then why were the specifications written as they were in the first place?  The specs should reflect what is needed.  The cost of construction (the bids) should not include meeting criteria that are 'over and above' the Owner's objectives.  The 'extra' cost is just economic waste.

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Howard Littman AIA
Forensic Architect, Expert Witness
Howard I. Littman, AIA
Agoura Hills CA
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the really short version answer is:
 If it is not a problem for the owner, then don't worry about the fact that the contractor missed the Ff Fl numbers. as Howard says ...record the event...and see if recovering "value" is worth the effort. Remember even parking garage floors can be a problem if they have too much difference between the hills and valleys of the finish! there are several garages in seattle where I can "bottom out" if I drive more than about 2 miles per hour.

However for future reference (and the next time the owner or interior designer requests 24x28 inch tiles.....

Long version:
1. I always specify an underlayment product as a "fix" tied to the Ff Fl discussion so that if the contractor misses those numbers and they DO matter, than there is a product to use to fix the issue.
2. I specify that the Ff and Fl are to be measured " At the time of FINAL floor finish" not at the time of concrete placement (yes the contractor will be upset about this) but I don't care about the first 24 hours after placement I care about the flooring sub trying to lay tile a year later on a washboard floor.  ASTM E1155M-96(2008) does not discuss the timing of the test just the test itself. The ACI document (302.1.R) talks about "preferably within 24 hours" and this is appropriate ...for the concrete sub....but perhaps not for the client when accepting the building a year later.

Use future specs to prepare for problems so the fix is accounted for ...not generated out of the back of the pickup truck.

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Marc Chavez CSI CCS CCCA AIA
Architect- Specifier
ZGF Architects LLP
Seattle WA
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