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Reply by clin

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Posted on Pocket holes for floating shelf?

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clin

1025 posts in 1358 days


#1 posted 07-14-2018 10:07 PM



I think those supports that @bilyo pointed out are pretty good. I believe they are intended to be mounted to studs and not to the drywall using an anchor. You should use several over the 5 run of your shelf. The only thing is that the supports require a shelf thickness of 1 1/8” to conceal the hardware and you might want to make the shelf slightly deeper—say 5.5”.

- Bill_Steele

I realize they mount to studs. My point is that the weight is trying to bend the bracket down. This will compress the drywall on the lower edge of the bracket (between the bracket and the stud). If the drywall compresses much at all, the bracket will tilt. I don’t think the weight of the shelf and typical knickknacks would cause this. But if the shelf is within reach, someone may put their weight on it. Heck, if I installed it, I’d probably reach up and grab it to help pull myself up after bending down to pick up my tools.

It’s simply the problem you get when the effective height of a supporting bracket is so small (less then 1”). It’s very much a leverage problem. A very short lever arm created by the short height of the bracket resisting the relatively long lever of the bracket extending into the shelf. So any force applied to the shelf is multiplied by the ratio of these “levers”. I think this would be in the range of 10:1 for a load along the front edge of the shelf.

So if someone put some of their weight, say 50 lbs, on the front edge of the shelf, it might put 500 lbs on the the nearest bracket. This force will concentrate on the lower edge of the bracket. Drywall compression strength is surprisingly low at about 400 PSI according to this link:

https://www.americangypsum.com/sites/default/files/documents/GA-235%20Gypsum%20Board%20Typical%20Mechanical%20and%20Physical%20Properties.pdf

So 500 lbs concentrated along the very edge of a small bracket would easily compress and begin denting the drywall. As it did this, the load would spread out over a larger drywall area under the bracket and would reach some equilibrium and stop, with the bracket tilted down. Of of course, maybe it crushes the drywall completely under the bracket.

I’d certainly consider those brackets and my guess is they would be just fine for the intended application (excluding the size issue Bill pointed out). I’m just pointing out what I think might happen and why.

-- Clin


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