Bad call

Had a sub pour a couple of decorative slabs today. 1 was straight sided (10 x 24) and the other was shaped like an egg/pear/water drop. (about 12 x 20) & definitely not round with NO straight side (s).
Point being, they missed the mud estimate by a yard. Damned near wound up cold jointed...would of required tear out.....both were 4" deep "graded" base. Will need to pour some more weird shaped slabs here.
? is how to calc a perimeter length by 4" deep and get cubic yards for future pours?
Dan
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Dan Deckert wrote:

Hire a different sub?
Perimeter & area are not related
rectangle 2 x 22 & square 12 x 12 both have same perimeter but greatly different area.
Draw to scale (1/4" to 1') on graph paper , count "large squares" & "small square" to get an accurate area estimate
Buy a mechanical planimeter, I got a cool antique one on ebay http://whistleralley.com/planimeter/planimeter.htm
Draw shape in drafting progam that does area calcs
cheers Bob
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Bobk207 wrote:

...
All good alternatives.
In addition, for a field at least "sanity check", outline the area similarly to the graph paper technique--lay out some squares/rectangles/triangles/circles that are easy to compute and that encompass the actual area. You will at least not be short and by judicious selection of areas, be pretty precise.
A yard at 4" depth would be roughly 80 sq-ft of surface area to give an idea of the precision needed and the amount their estimate was off by.
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dpb wrote:

I think your field sanity check is better idea....no drawing, just cut up the area in some rectangles / squares & use your 80 sq ft number.....round up to nearest 1/2 yd & your good to go.
cheers Bob
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One other thing to remember: An error in the smallest dimension produces the greatest shortage/overage. Make sure the depth is accurate. This can be easily missed when casting slabs on grade. Is it really 4"? If it's 5" you're going to off by 25%. On a 10 yard pour, that's pretty significant.
I'd rather be throwing an extra yard away than finding myself a yard short.
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Bobk207 wrote:


In Sketchup, select the surface, right click, select area of selection, click. Done to four decimal points. Then multiply by the slab depth in feet (4" > .33')
R
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Thanks all for answers/suggestions. I looked to high heaven for a calc. I could use the perimeter distance with to no avail.
Rico, I did run it thru SK5 but was trying for a perimeter solution. I've always 'boxed' the pour in segments as suggested but was hoping there was a way to do it thru a perimeter measurement.
Dan

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Dan Deckert wrote:

The only way the perimeter shape will do you any good is using a planimeter.....tracing the perimeter with a planimeter will give you the area.
cheers Bob
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