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I am putting up short sections of aluminum fencing inside my patio in the back and up one side, to deter people & pets from jumping off the patio at those points. A gazebo is going to be permanently set up on this patio, inside the fence sections.

I am going to set the aluminum fence posts into concrete. The posts provided are 56" tall, the fence panels are 45". I live in Maine, so I need to put forms in and set them below the frost line (4') yet it states in the installation directions that "The posts themselves do NOT have to go below the frost line, however, for proper installation."

My question is, how do I keep the fence post at the proper height and plumb, if it is not going to have the stability of reaching the bottom of the hole?

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    Aluminum really should not be in direct contact with concrete, it will corrode big time... – Jack May 16 '17 at 3:14
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    To add to Jack's comment, aluminum is so reactive with concrete that it is the ingredient used to make concrete "foam". Aluminum powder is added to the concrete and the reaction fills the concrete with gas bubbles. Instead of concrete, consider something else, like gravel, There's also an expanding foam similar to Great Stuff that's rated for ground contact and sold specifically for setting fence posts. Another approach is fastening mounting brackets to the top of the concrete after its cured and use those to hold the posts. (cont'd) – fixer1234 May 16 '17 at 5:47
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    Still another approach is to use PVC pipe that fits snugly around the posts. Cap the bottom of the pipe and embed that it the concrete. Then slip the post into the pipe. – fixer1234 May 16 '17 at 5:47
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    Aluminum in concrete is "nope". I would probably go for an FRP rod that is snug (or snugged) to the inside of the aluminum tubing, FRP is inert inside concrete, unlike steel. An alternative is PVC pipe inside the aluminum and steel rod inside that, the latter set in the concrete to full depth. By "is snugged" I mean spacers of some kind, e.g. Go deliberately undersize and make up the differnece with a few turns of duct tape near top and bottom. – Harper May 16 '17 at 16:30
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    Fence post footings needn't be to frost depth. In fact, I've never seen one that is, and I'm in Minnesota. – isherwood May 16 '17 at 16:55
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The forms have a top. You temporarily attach something to the post that holds it at the proper height when sitting on the top of the form, and you set a couple of temporary wooden stakes at 90 degrees to each other from the form that hold diagonal braces that hold the post plumb, and leave all of those in place until the concrete sets. With aluminum posts this might involve a lot of clamps to hold the post to the braces and supports.

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    I would agree this method is the way to hold it but I would not put aluminum in concrete. – Ed Beal Jan 30 '18 at 19:42

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