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I'm adding a new gate in my vinyl fence; a full width (6') gate.

I'm concerned about support. The fence posts are decently moored, but there is still some wiggle.

Would it be better to dig out and add additional concrete around the outside of the posts and keep the posts hollow?

Or would it be better to add a 4"x 4" wood post insert and moor it with some interior concrete to moor it?

Or is there another approach?

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I always use a 4x4 inside of vinyl posts to make sure they stay straight. Also, a six foot wide gate hooked to one post concerns me due to the weight and length. Since I don't how heavy your gate is I can't say how deep I would dig for the 4x4, but three feet, and one eight pound bag of concrete is what I'm guessing would keep the post straight. Also, I'd dig the hole bigger at the bottom for additional support. – getterdun Jun 17 '14 at 2:16
@getterdun - make it an answer, and I'll accept. – Jason Jun 17 '14 at 19:38
I'm tempted to suggest two 3' gates. I know that's less convenient for a car, but it avoids putting as long and heavy a lever-arm on the post. Or perhaps put a wheel at the far end of the gate... – keshlam Oct 3 '14 at 4:58

I filled the posts of my gates with Sakrete concrete. It's strong enough that when my large gate swings wide enough that single post ends up holding the weight of the entire gate. e.g. the ground level drops a few inches and the wheels lift off.

Just buy a bag of 60lbs Sakrete. Dump it in the post dry and use the hose to add some water. (You can mix if first if you want but this worked just fine for me). Just make sure to also wash away water mix that comes out of the bottom of the post or else it will stain.

However, I am now facing an issue where in high winds my small gate buckled and the steal anchors bent. The hinges on the small gate are all bent out of shape since it bent inward. If I had it to do over again, I'd probably go for two smaller gates instead of one 6' and one 3'.

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Get rid of the concrete, unless maybe, you're dealing with sand, high sand content or arid conditions but those are super easy to go deeper in. I've yet to notice any benefit, at all, to using concrete. It doesn't preserve posts, it's not any stronger, it's not any quicker & it retains & wicks water very much longer.

Yeah, 4x4's are great up to 3' for railings, but even those flex noticeably. I'd suggest a 6x6 or at least a 4x6 if you want the public side kept to scale. The 4x6 would give you the extra beef to minimize door swing sag or bounce along the swinging path.

Of course, screw the 4x6 to the end fence post (which there should be) or screw 2 4x6's to each other at the end of the fence. Vinyl is heavy & a framed gate (which it better be) is really heavy...compared to wood.

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Dig a 6in. deep trench 4ft. long opposite direction of your gate when closed! Do this against the post revealing some of the post. Fill with concrete and let set then hang your gate! The concrete will be pushing against a larger area creating less pressure against the area of just the post. Like a brace! If you don't want to see the concrete dig deeper to allow for back fill!

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