Post Holes for Dummy Fence Builders Part 2

Post hole

We aren't kidding when we suggest that, some days, this blog darned near writes itself. Take this coincidence, for example: just yesterday, we were exposing one eHowian for telling us how to calculate the volume of cement needed for post holes – and getting it wrong – when what to our wondering eyes should appear but another eHowian expounding on precisely the same subject, and getting it wrong, too. What makes this episode of serendipity particularly juicy is that it was eHow.com themselves who provided us the link to the new content, smack-dab in the middle of the page under the bold heading "Other People Are Reading..." Sadly, however, their second contributor, a self-described "professional writer" named Bryant Harland, proved no more competent to explain the procedure than was the guy we featured yesterday. For proof, read what Harland has to say in the piece titled "How to Calculate Concrete for Fence Posts."¹

As we pointed out yesterday, Larry Simmons managed to forget almost entirely (if, in fact, he ever knew) that you don't fill a post hole with cement and then set the post on top of it after it dries -- that would be a pier, for those of you keeping track. No, you set the post in the hole and then pour mixed cement around it. Well, Bryant suffers from the same deficiency in knowledge (or, perhaps, common sense).
Harland's solution to calculating the concrete needed to set fence posts uses slightly different dimensions from that of Simmons. Bryant wants to use post holes six inches across (he seems afraid to use the word "diameter") and 36 inches deep. He does the math, just like Larry, using the formula for the volume of a cylinder: V = h * π * r² (where V is volume, h is the height of the cylinder, r is the radius, and π is approximately 3.14). 

Though it's deeper by 20 percent, Harland's post hole is significantly smaller than that envisioned by Simmons - that's because the radius is three inches instead of four. Bryant says that the volume of his example post is 0.59 ft³. Once more, we find no fault with either his application of geometry or his application of simple arithmetic. Where we do find fault is with Harland's failure to remember that a fence post will go into each hole before he pours in the cement mix! If you place a 4 x 4 fence post in each 36-inch hole, the wood occupies 441 in³ of space – a figure approaching half the volume of the hole!  Bryant's 0.59 cubic feet per hole estimate is immediately reduced to 0.33 cubic feet!

All we can say is thank heavens this guy (and his friend Larry Simmons) aren't estimating materials for a construction company, because they wouldn't keep their jobs for long! We just don't know whether the two should share one Dumbass of the Day award, or we should give each of them one and hand eHow.com a third for letting not one but two people make the same dumbass mistake. Sheesh.

¹ The original has been deleted by Leaf Group, but can still be accessed using the Wayback machine at archive.org. Its URL was   ehow.com/how_5597665_calculate-concrete-fence-posts.html

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DDIY - FENCES