Expanding foam to set fence posts - OB opinions?

I would never trust that to something with mixed reviews. It doesn't take much horsepower to pour a bag of quikrete in a hole. I would go with concrete.

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I would never trust that to something with mixed reviews. It doesn't take much horsepower to pour a bag of quikrete in a hole. I would go with concrete.

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This

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In our tests, we actually get better performance results with Fast 2K than with concrete in terms of resistance to lateral force. The post does not break as easily with Fast 2K as it does with concrete. Concrete is very rigid and has no give to it, so the total lateral force is on the wood post. Fast 2K absorbs some of the force and has a little give to it so the post does not break.

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This section from their FAQ would give me pause. Sure, the post may not break as easily, but if the foam doesn't rebound after loading, your fence posts may be permanently loose or wobbly.

These kinds of materials (though probably not quite the same) are used in commercial construction, though they are often injected into soil rather than cured in an open hole. The combo of the soil/foam matrix is normally a good bit stronger than the foam itself.

I'd just use concrete.

pole depth, surface area of pole, difficulty in digging down around pole to fix a wobbly one, etc. are all different with telephone poles vs fence posts.

Spinoff question: I dug my holes for the posts this weekend with an auger, and it appears I'm below the water table at 2 and a half feet. There's about 8 inches of water in every hole. Will the posts rot quicker if I put them directly in water like that and then pour concrete? I've read that you should put a few inches of gravel at the bottom to allow for drainage, but that's not gonna help if the bottom is always filled with water. Should I treat the bottoms with something?

I have a horse farm in Missouri. I put all of my posts in the ground with foam. My horses are very hard on the posts and as long as the posts are not in wet ground they stay where I put them. I will not do it any other way. Its easy and I can install a fence line in one day! My husband thought I was crazy but when he came home I had all the posts set and ready to string wire. I love it!! Mix small batches at a time! Get all your posts ready and pour. I use small sticks to hold the posts up while drying.

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if you use enough of the bagged concrete - it can and does cause breathing problems and other health issues. Even if you wear a mask - the amount of this stuff that gets onto your clothes and eyes is not good.

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The person that is buying expanding foam for fence posts isn't going to be using enough bagged concrete to gag a gnat. This is like saying use flex seal instead of welding the pinhole in the bottom of your aluminum boat to protect your skin and eyes.