Expanding Foam for Setting Fence Posts

[BrentDH]

Does anyone here have any experience with using that new two-part expanding foam for setting fence posts?  I am going to be setting up a trellis to contain some raspberry bushes.  Envision three cross shaped posts in a row with cable through the cross pieces.  There will be some tension to get the cable tight and the bushes themselves will add pressure as they grow and lean on the cable.  I was going to put the fence posts 3' in the ground and 5' above ground.  I also am actually planning on 3 cross pieces at 2', 3.5' and one at the top at 5'.  My original thought was to just tamp dirt around them, but I saw that expanding foam stuff and wondered if it would work any better to avoid the eventual lean in the direction of the tension.  Thoughts?

[crokett™]

If the 3 posts are cross braced to each other, then I don't think you need expanding foam. I would put gravel around them to help the water drain away. We cross brace corner posts on high tension live stock fences to another post and they don't move. We just set them in the ground.

[FireWood]

I've used it for light duty stuff like a mailbox.  It is quick and easy.

I'd say it's about as secure as lightly tamped dirt, but it is not as secure as properly tamped clay or crushed stone.

It moved when I bumped it with the mower, and moved back when I tried to straighten it.

I wouldn't use it for a trellis.

[BrentDH]

I wasn't planning on any cross bracing but that certainly would eliminate the leaning concern.  Youtube videos show a very mixed bag (pun intended) of results with the expanding foam.

[mound]

Does anyone here have any experience with using that new two-part expanding foam for setting fence posts?  I am going to be setting up a trellis to contain some raspberry bushes.  Envision three cross shaped posts in a row with cable through the cross pieces.  There will be some tension to get the cable tight and the bushes themselves will add pressure as they grow and lean on the cable.  I was going to put the fence posts 3' in the ground and 5' above ground.  I also am actually planning on 3 cross pieces at 2', 3.5' and one at the top at 5'.  My original thought was to just tamp dirt around them, but I saw that expanding foam stuff and wondered if it would work any better to avoid the eventual lean in the direction of the tension.  Thoughts?

I built an ~130' cedar fence, oh, it must be 8yrs ago now, and set all the posts with the stuff. It held strong and worked quite well with the exception of 2 or 3 posts in a low and always wet area of the yard, I ended up re-setting those in concrete. The rest held up very well!

[Bill Tindall]

Does anyone here have any experience with using that new two-part expanding foam for setting fence posts?  I am going to be setting up a trellis to contain some raspberry bushes.  Envision three cross shaped posts in a row with cable through the cross pieces.  There will be some tension to get the cable tight and the bushes themselves will add pressure as they grow and lean on the cable.  I was going to put the fence posts 3' in the ground and 5' above ground.  I also am actually planning on 3 cross pieces at 2', 3.5' and one at the top at 5'.  My original thought was to just tamp dirt around them, but I saw that expanding foam stuff and wondered if it would work any better to avoid the eventual lean in the direction of the tension.  Thoughts?

I have lived on a farm most of my life, attended high tensile fencing school, and participated in several USDA cost share projects where fencing was specified by the Ag engineer.  At school we set two terminal posts with a brace and stretched 330' of high tensile cattle fence so tight against these post that the entire run stood erect.  There were tons of force on these posts. The posts were set 3' deep and secured with tamped earth.  I recently won a round with a civil engineer over setting posts for a trail bridge approach.  He wanted concrete.  Concrete is not recommended by either the Ag department nor the highway department.  Across the land wood guard rails are to be set in tamped earth.  Alternatively crushed rock with a distribution of particle size can be used.  If your dirt is dry enough to compact that is all that is necessary.  Here on my farm some areas are sandy and I used "crusher run" rock from the quarry.  All my fencing is high tensile so there is considerable strain on the posts.  Your needs are modest by comparison.  

Concrete is not recommended for posts for it promotes rot.  The expanding stuff could have a similar adverse effect.

[JDuke]

I have lived on a farm most of my life, attended high tensile fencing school, and participated in several USDA cost share projects where fencing was specified by the Ag engineer.  At school we set two terminal posts with a brace and stretched 330' of high tensile cattle fence so tight against these post that the entire run stood erect.  There were tons of force on these posts. The posts were set 3' deep and secured with tamped earth.  I recently won a round with a civil engineer over setting posts for a trail bridge approach.  He wanted concrete.  Concrete is not recommended by either the Ag department nor the highway department.  Across the land wood guard rails are to be set in tamped earth.  Alternatively crushed rock with a distribution of particle size can be used.  If your dirt is dry enough to compact that is all that is necessary.  Here on my farm some areas are sandy and I used "crusher run" rock from the quarry.  All my fencing is high tensile so there is considerable strain on the posts.  Your needs are modest by comparison.  

Concrete is not recommended for posts for it promotes rot.  The expanding stuff could have a similar adverse effect.

Does soil type play into the calculation?

How about post type?

I’m thinking your soil type holds together better than the 1-2 feet of sand here in east Texas 

I built a pipe fence 1500 feet along front of my property and used 160lbs of concrete each for both sides of H braces at ends of run set at least 3ft in the ground for the line posts, I drove pipe 3-4ft into the ground and welded a top rail the entire length.

I have no doubt that in most soil and wood posts, that tamped earth is best, but for 1-2 feet of sand with clay below that, I doubt it would hold up well.  The sand just pushes away to easy with much pressure. 

Just my uneducated opinion, please educate me if I’m wrong.

[Bill Tindall]

Does soil type play into the calculation?

How about post type?

I’m thinking your soil type holds together better than the 1-2 feet of sand here in east Texas 

I built a pipe fence 1500 feet along front of my property and used 160lbs of concrete each for both sides of H braces at ends of run set at least 3ft in the ground for the line posts, I drove pipe 3-4ft into the ground and welded a top rail the entire length.

I have no doubt that in most soil and wood posts, that tamped earth is best, but for 1-2 feet of sand with clay below that, I doubt it would hold up well.  The sand just pushes away to easy with much pressure. 

Just my uneducated opinion, please educate me if I’m wrong.

Both the USDA and US Department of Transportation offer recommendations when tamped earth 32 to 36" deep is impractical.  On the bridges we are building it is occasionally impractical to drill a hole, or the location of the post is in recent fill.  Where the posts will be set in a trench dug with an excavator, or in loose soil, there are two options.  A concrete tube can be installed with post inside and filled with crusher run rock.  Or the wood post can be isolated from the concrete with a polymer barrier material and the post set in concrete.  I have no experience with steel posts so I can not offer any advice on setting them.

[BrentDH]

Thanks for all the feedback.  I think I will just go with my original plan of tamped earth.  The soil on my property is pretty good so it should pack well.

[Snipe Hunter]

My concern with the foam would be that the posts would all be top heavy. Just doesn't sound like a good alternative to concrete. Foam "may" anchor ok but will it degrade? Concrete won't degrade and it's bottom heavy. I like the physics of the concrete.