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concrete in backyard. How do we measure its size?

Hello

I have a backyard contractor and we both agreed on $7.50/sq feet for stamped concrete.  The work is finished and it is time for the payment. (I have paid majority of the money though as work progressed). The concrete is in curves and irregular shapes and the problem is how to measure the total area.
Contractor started with his logic- 23 yards of concrete (some of which he did use for bullnose caps etc) and at 4" thickness (not sure it is safe to assume that it is 4" everywhere or on average), it is 1863 sq feet. (23 yards = 81 sq feet of 4" thick * 23= 1863 sq feet). 
On my side, I put all the curves and shapes pretty accurately in Google SketchUp software (which I had used from begining for designing my backyard) and my measurement comes to 1607 sq feet. 
I am novice in the home improvement field (but my design and measurements are pretty accurate and I am a finance guy/computer engineer by profession.) so looking for some professional advice here. How can we come to an accurate figure? What is industry practice to measure concrete areas?
Thanks in advance for your time and help.
  
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July 13 2009 - US
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Answers (7)

Best Answer
From a concrete contractor,

  He should have qouted you square footage prior to start. Vague contracts going into it are meant to scam. That aside, you are stuck if he has started. When measuring, break down each section into simple geometric figures such as rectangles and triangles, and for curves, fit a straight line through them to average it together. This will be quite accurate. Your computer program should work halfway decently also, but it is best to do the measurements with him there, in order to agree on the measurements. 
    As far as his comment on the yardage, kick it to the curb. Many contractors have difficulty calculating yardage properly, due to lack of proper prep work with grading at a consistent 3.5-4 inches, and order much extra to make sure they arent short. I have even seen some order 10 yards on what should have been a 3 yard job, because the homeowner was paying the concrete bill, and he didnt want to take the time to figure it right. Most contractors that are even halfway decent will overshoot by 1-2 yards, and I, who is extremely particular about waste, still have to add .5 yards, becuase it is hell when you are short.
Keep in mind that if this was the setup to begin with, this was his plan all along, and could have added a couple of yards just to pad his pocket.
    If there is a problem, remember, the law is on your side for this. In California, if he is licensed, he must provide a complete bid, prior to start, and if you file a complaint, he will have big issues. If he isnt licensed, he has no rights in court, per state law, and will lose in a civil case if he takes you there. This is his goof, and he should know better. I never have open ended contracts, except for very particular jobs, where it must be time and materials, and I even hate doing that. He should know better. Stand your ground.
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July 13 2009
If he was talking cubic yards of concrete, not square yards (they order it from the plant in cubic yards). each cubic yard is equal to 27 cubic feet. 1 yard x 3 feet high x 3 feet wide x 3 feet deep x 23 yards of concrete  equals 207 square feet of concrete if you convert 207 square feet of concrete to a continuous 4 " thick slab and you will have to assume this is the case. you get 207 square feet x 3 equals 621 square feet of a 4 " slab of concrete. But then 621 x 7.50 is $4,657.50. Maybe he was working in square yards?... But there's a point to clarify. And a point to talk about with him.
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July 26 2009
if there were changes, he should have provided a written extra, prior to extra being done. His price is by foot, not by yard. Stick to your guns, and measure it with him there, and if he doesnt want to measure it, dont give him anything till he is willing, and file your complaint with the license board. You are right, he is a trying to take you.
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July 25 2009
Profile picture for profitfromprices
Thanks everyone for your help.

Though he is a licensed contractor, there was no contract as such. I signed on his cost estimates which were based on the plan I had created with Google SketchUp software. As the work progressed, we had some changed here and there (like basketball court, we changed it from 28x28 feet to 28x31 feet etc.) We both had talked in the beginning that the final payment will be based on actual square footage (actual area of concrete that we end up with).
At the end, I updated my plan with exact dimensions of concrete, retaining wall etc. Google SketchUp then helps you calculate any weird shape accurately.
The thing is: he wants to derive the area based on his math: Yards of concrete used and with assumption that no concrete was wasted and it is 4" uniformly placed everywhere. I do not know how much concrete the truck took back unused!!
I am telling him to measure the concrete and find the actual square footage which I have done with help of the software which he can verify at any random points in my map.
Or, is there any service or consultant that can help us do the measurement as a third party?

Thanks again for all the help.
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July 23 2009
I think Titan's answer is exactly right. Check your agreement carefully, demonstrate where you got your numbers from.
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July 23 2009
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Uh, the price and measurements should have been agreed upon and a contract signed prior to the start of the work.  This is no time to be quibelling about the finished job.  If you have a signed contract, the contractor can place a lien upon your house until you pay the full amount.  I too am a computer guy but if you are happy with the contractor and the job, I would pay up instead of nitpicking.  4 inches of thickness can vary plus or minus a little and some type of variation should be built into the contract so that the mixer truck has more concrete onboard instead of running out of concrete during the job.
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July 13 2009
The correct answer is to put the measurements in the software when the forms are up and agree on size. In your shoes I would take his 1,863 and your 1,607, explain and offer to pay on 1,735 but that's just me. best of luck! 
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July 13 2009
 
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