| Author |
Message |
Don Harris CSI, CCS, CCCA, AIA
Senior Member
Username: don_harris
Post Number: 130
Registered: 03-2003
| | Posted on Friday, April 13, 2007 - 03:24 pm: |    |
Had an e-mail correspondence recently regarding flatness testing. Owner thinks it is unnecessary because there are no specialized floors (basically an academic/office use) requiring special flatness levels. He goes on that he's worked with the contractor before and trusts him to do a good job. We specified overall values of flatness, F(F) 35; and levelness, F(L) 25; with minimum local values of flatness, F(F) 24; and levelness, F(L) 17; for slabs-on-grade.
Is it necessary to specify Ff and Fl numbers for an ordinary floor? Is it money well spent? Does anyone ever not specify flatness requirements and just rely on ACI? Is this one of these things we specify because "we've always done it that way"? Thanks in advance. |
Ralph Liebing, RA, CSI
Senior Member
Username: rliebing
Post Number: 589
Registered: 02-2003
| | Posted on Friday, April 13, 2007 - 03:44 pm: | |
'.....worked with the contractor before and trusts him to do a good job. is not a very sound basis for a project. Our interors people love to do thsi, all the time [!!!!!]
If the floor proves faulty, who enforces what? What in fact is enforcible? Is this creating a "contract" outside the contract? Is there a true basis for quality assessment? Will the owner willingly[???] go after the contractor, or will your office be "scored" for not specing flatness, etc.
Even the most minimal provisions is preferable to ":nothing"!
Good well-founded contracts rely on good, clear and spcific requirements.
Not preaching, Don, juts loading your gun for the client!!! |
Don Harris CSI, CCS, CCCA, AIA
Senior Member
Username: don_harris
Post Number: 131
Registered: 03-2003
| | Posted on Friday, April 13, 2007 - 03:48 pm: | |
Got it! Thanks Ralph. FYI, The requirements are in the contract, the Owner just wants to save the money for something that he sees as marginal. |
Ralph Liebing, RA, CSI
Senior Member
Username: rliebing
Post Number: 590
Registered: 02-2003
| | Posted on Friday, April 13, 2007 - 03:54 pm: | |
Brand new old saying/axiom!!!!
NOTHING IN SPECIFICATIONS IS MARGINAL!!!!! |
Anne Whitacre, FCSI CCS
Senior Member
Username: awhitacre
Post Number: 518
Registered: 07-2002
| | Posted on Friday, April 13, 2007 - 04:34 pm: | |
Don-
for interior work like you mentioned, I usually just go with the 10' straightedge measurement. the problem I see with the F numbers is that no one in the architectural office has the laser thingey to measure that and you have to do a lot of points to get the reading. with a 10' straightedge, everyone can see it and its pretty low tech.
I regularly relied on just the Class B finish, and then required the contractor to put in a leveling course if they didn't meet those minimal requirements. if they were in a hurry and did a bad floor, then they had to level it. if they did a great floor, then they didn't have to take the extra step. |
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues
Post Number: 659
Registered: 10-2002
| | Posted on Friday, April 13, 2007 - 04:59 pm: | |
Ah, Anne, I was waiting for that, you brought up my main complaint about this system with the flatness numbers. I so totally agree with you.
In addition, what a lot do not realize is that the measurements when using the fl numbers must be taken within the first 24 hours after the concrete is poured and if later than that it is considered invalid as a test.
As far as the quality of the floor (by whatever measuring system) being unimportant to office academic use, that's just plain uninformed about what other finishes require - as well as placement of furniture. Maybe he just likes using shims under all the desks or every has to have a 3 point chair. |
Don Harris CSI, CCS, CCCA, AIA
Senior Member
Username: don_harris
Post Number: 132
Registered: 03-2003
| | Posted on Friday, April 13, 2007 - 05:15 pm: | |
I agree with all your comments. This owner is just being hardheaded about paying for the tests. We have also stressed William's point regarding equipment, shelving and furniture.
We have had the conversation with the Owner and documented the situation. If they get a handicap ramp instead of a floor they are not to call us.
I never had a major problem with the straightedge method. Maybe I should just go back to it. |
Mark Gilligan SE, CSI
Senior Member
Username: markgilligan
Post Number: 157
Registered: 05-2005
| | Posted on Saturday, April 14, 2007 - 02:34 am: | |
I agree with Ann. Unless there is a special concern, specify 1/4" with a 10 foot straight edge. This establishes the basis for rejection if there are problems. A lot of floors have been constructed using this criteria and there are relatively few problems. The testing costs should also be low. |
John Regener, AIA, CCS, CCCA, CSI, SCIP
Senior Member
Username: john_regener
Post Number: 281
Registered: 04-2002
| | Posted on Sunday, April 15, 2007 - 12:32 am: | |
What does 1/4" in 10 feet mean? Is it + 1/4" or - 1/4" or both (accumulated difference of 1/2" between high and low spots)? This is what I understand is the major problem with the 1/4" in 10 feet standard.
As far as I know, there is no laser involved in the testing process. A "Dipstick" device is used to mechanically measure the differences in flatness and levelness across the floor slab. The resulting statistics yield Face numbers (FF = flatness and FL = levelness).
All that is moot if the party in charge (Owner or CM) insists on not following the specified Face numbers but use the 10 foot straightedge measure. It should be noted that the contract includes the FF/FL testing and reporting, so contractually a Change Order should be executed to adjust the Contract Time and Contract Sum.
Note that there are a few issues beside the visual appearance of the floor. Casework placed on a wavy floor will need to be shimmed and scribed in order to be level. Base, especially wood, stone or tile, will need to be adjusted or trimmed so the top edge is level if the floor fluctuates. |
Mark Gilligan SE, CSI
Senior Member
Username: markgilligan
Post Number: 158
Registered: 05-2005
| | Posted on Sunday, April 15, 2007 - 03:48 am: | |
The 10 foot straight edge rule is less precise but it is fairly simple. You put the 10 foot straight edge down and verify that at no place does the gap exceed 1/4". If you want to be tighter specify 1/8" maximum.
In most cases this approach will result in an adequate floor. A lot of floors were built using this approach. Obviously you would use the F numbers if you had a building with high storage racks and automated fork lifts.
While the existing specification calls for the use of F numbers Don asked if there were other ways to handle this problem.
I appreciate the need to deal with the interface between the flooring and the casework but this issue does not go away when you go to the F numbers. Depending on the value of the F numbers specified you can still have the fluctuations. The advantage of the F numbers is that they allow you to evaluate the performance with greater precision and consistency. You can select more restrictive criteria but this will cost you more and in the end it may be better to deal with the normal slab variations.
One problem that the F numbers will not solve has to do with suspended slabs. The flatness of the floor must be measured before shoring has been removed thus this will do nothing to deal with floor deflection issues. Dealing with floor deflection can play havoc with long runs of casework and sliding partitions. Making the floors stiffer is not always very feasible.
What is ultimately comes down to is balancing of risks. Sometimes it makes sense to be more flexible. |
Helaine K. (Holly) Robinson CSI CCS CCCA
Senior Member
Username: hollyrob
Post Number: 313
Registered: 07-2003
| | Posted on Sunday, April 15, 2007 - 10:26 am: | |
I thought the F number system was developed because the 10 foot straight edge rule was not supposed to be consistent or accurate? |
Mark Gilligan SE, CSI
Senior Member
Username: markgilligan
Post Number: 159
Registered: 05-2005
| | Posted on Sunday, April 15, 2007 - 02:01 pm: | |
Holly you are correct but in many situations the 10 foot straight edge may be accurate and consistent enough. Depending on the intended use your expectations may be less and the 10 foot straight edge may be sufficient to reject the significant variations.
It might be interesting to identify a number of floors where there have been no problems and determining their in-place F numbers. I would not be supprised to find a lot of floors "out of tolerance". The selection of the target F numbers is subjective. |
Kenneth C. Crocco
Senior Member
Username: kcrocco
Post Number: 93
Registered: 04-2003
| | Posted on Monday, April 16, 2007 - 11:22 am: | |
The 10 foot straight edge is inconsistently applied and gives inconsistent results depending on how it is used. For 1/4 inch in 10 feet, try placing two spacers, one on each end of a 10 foot straight edge. Next place the straight edge with spacers on the floor; it must sit on the spacers without rocking. you now have a 10 foot straight edge raised up 1/4 inch from the flat plane. The inspector then runs a 1/4 inch diameter ball under the straight edge; the 1/4 inch ball should not pass through the gap at any point.
If an inspector uses a straight edge without spacers it is difficult to properly deal with high points; the straight edge rocks; try it yourself on an uneven floor.
The other thing we learned is that 1/4 inch in 10 feet is rairly achieved without leveling.
We specify both methods depending on the project complexity and requests from clients; meaning 10 foot straight edge or F-numbers; mostly F-numbers. |
Bob Woodburn
Senior Member
Username: bwoodburn
Post Number: 185
Registered: 01-2005
| | Posted on Wednesday, April 25, 2007 - 12:03 pm: | |
Ken, if the straightedge is on 1/4 inch spacers, a 1/4 inch ball would run under it at the slightest depression. Isn't that "zero tolerance"?
If a maximum 1/4 inch gap under the straightedge is permissible (w/o spacers), wouldn't you use a 1/2 inch ball with the 1/4 inch spacers? |
David R. Combs, CSI, CCS, CCCA
Senior Member
Username: davidcombs
Post Number: 230
Registered: 08-2004
| | Posted on Wednesday, April 25, 2007 - 12:11 pm: | |
And if the 1/2 inch ball were to pass under the straightedge at mid-point, with the straightedge up on 1/4 inch spacers, wouldn't that be 1/4 inch in 5 feet? |
M. Purdue
Intermediate Member
Username: super_slo
Post Number: 4
Registered: 04-2007
| | Posted on Sunday, April 29, 2007 - 12:45 am: | |
Hi guys and gals.....I've been away whilst I rebuilt my computer. No easy task I might add.
Back to the subject at hand......Just a note on a trick I learned. Pour the concrete, cut the joints ASAP, THEN apply the curing compound. If that is not possible,( sometimes we cut them the next morning ) spec. that the cutting powder be removed completely, then spray the cut with cure. I've seen perfectly flat slabs curl at the sawcuts to the point they had to be ground down to apply flooring. Slabs are particularly sensitive in dry windy weather, as well as hot temps. |
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