Setting Posts in Concrete vs. Gravel vs. Expanding Foam

[Fix2Relax]

I have six 4x4 redwood posts that need to be anchored to support privacy screens. Holes are dug and are about 12 inches diameter, 30 inches deep. Post will be about 5 feet above ground (2.5 feet buried). Located in Tucson, Arizona so no frost issues. Very little loading on the posts themselves. Been looking at the Sika Post Fix, costly but easy to transport compared to concrete or gravel but from what I read it's tricky to handle because of the need to immediately pour the mixed product into the hole before it starts to expand. Options for cement and gravel are easy and cheap but a PITA to get the bags of product to the jobsite. Obviously just dumping and compacting gravel would be the easiest but I wonder what would be the most effective.

Comments would be greatly appreciated. Thanks.

David

[Splinter Puller]

if the post are lightly loaded just tamp them in place with dampened gravel. Billions of farm fence post are just placed into the earth and tamped.

[jteneyck]

I would agree with that except if the wind load is going to be a concern. If the privacy fence has significant area there could be a lot of wind load, unlike with a fence post.

I had a privacy fence installed by the "pros". Supposedly they set the posts 40" deep in concrete. Turns out they used the type of mix you just dump dry in the hole w/o water, and the ground moisture is supposed to set the concrete. It never set and within a few years the fence was flopping back and forth in the wind. I had to take it all out and do it right. It hasn't moved since.

In the end, you only have to carry the concrete once.

John

[Woodenfish]

You can straighten a wind damaged fence far easier if set in tamped crushed limestone than in concrete. Leaning concrete posts need to be dug out.

[meackerman]

the fence posts I've put in to contain the horses are all set in gravel. Pretty decent holding power...my son hooked my compact tractor's bucket on one while we were installing and spun the tractors wheels...only leaned the post over about 5 degrees. Just enough to be noticeable...but since it was gravel it wasn't too hard to plumb it back up.

But the fence is strung with wire so there's no wind load on it.

[messmaker]

We have clay around here, but a post planted that deep should be fine just tamped if it is not subject to a lot of lateral force.

[woodgrain]

If you go the gravel route, the type of gravel makes a difference also. Here I would use a 5/8" minus, unsifted (with all the powder the comes from the crushing process). This mix compacts very tightly unlike a uniformly rinsed crushed rock.

[Admiral]

woodgrain said:

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If you go the gravel route, the type of gravel makes a difference also. Here I would use a 5/8" minus, unsifted (with all the powder the comes from the crushing process). This mix compacts very tightly unlike a uniformly rinsed crushed rock.

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This. Put some in the bottom too for drainage.

In my neck of the woods, this is called "quarry process stone"

[meackerman]

us too. and nice layer of hardpan about 3' down.

got my post hole digger on my tractor stuck in it....that wasn't so much fun to get back out

[daddo]

What's a "privacy screen" and what sailing ability does it have?

If there is a lot of resistance, perhaps a double set post with a cross brace every so often would help prevent leaning.? Perhaps staggering the posts?
Relief flaps?

We hit one of those straight winds near Tucson before and they can be so bad we couldn't get the big van above 50 mph.