Fence Post Foam vs Concrete | STRENGTH TEST

I rarely ever weigh in on comments but I have to on this one. I have a large acreage and have foamed in over 150 5” and 6” posts, along with numerous 4” and 6” square posts. Expanding foam works better and expands more if the temperature is above 70 degrees. I do not use , but have used, the SIKA prepackaged foam. I buy the foam I use in 1 gallon containers and mix with a drill, proper mixing is absolutely key!!! I have had to pull several end posts to put gates in and they hold great. Plus when I pulled the posts, I used a saws all with a 18” blade to cut off the foam. The post was completely dry, it had been in the ground 6 years and looked brand new still. I let the foam rise above the ground and use the saws all to make a small cone from post to ground so the water runs away. The foam is a bit more expensive then concrete but a lot less work! Concrete is porous and actually absorbs water like a sponge. Concrete never truly sets for years, the chemical reactions (hydration) is what causes it to cure. Concrete wants to absorb water and causes the wood to rot sooner or later. The weight on the bottom of the post is nice but the wood will eventually rot. Foam seals the wood, it will not rot or absorb moisture, sealing it. Foam “shrinking” is not a thing. The ground around it can shrink due to less moisture but the foam does not. Improper packing of the soil before placing or water saturated soil is the cause, not the foam. It can not shrink, it dries to a very hard substance. Concrete does the same thing, if the ground surrounding it wasn’t untouched soil or compacted properly, something better than a 2x4, it will move when the ground shrinks too. If you make your post hole a slight bell shape at the bottom, the frost locks it down. Ground freezes from the surface down. Doing this helps to stop any heave from a deeper freeze. Also, if you move the curing foam or improperly mix the foam, it can create voids . But it will not if you follow the instructions. If I get the mushroom around the post from the foam, I just add a bit of new foam to seal it and then shave it down when cured. Power and telephone companies have been using foam for years as it is far superior, my father worked for a Rural Electric Company for 35+ years and remembers when they first started using foam. He said it was a game changer. I have used foam for over 10 years on every type of fencing and miles of barbwire, we stretch the wire and have never had a problem. Sorry for the long post, I just read so much bad information and had to chime in.

3 years ago I installed a fence using the same foam you tried. My exp. so far is very good. No movement and the fence is holding up through winters well. I used 2 bags per post because I used 3 foot deep holes with gravel beds at the bottom for a drain. I did concrete in some of the posts that were shallower due to ledge. The concreted posts all have 3 half inch rebar glued into the ledge. They don't move at all but took 10 times longer to install. Over all if you need a mail box or some free standing post that doesn't benefit from the concrete's mass, I'd use the foam.

Thanks, you make a great point between the two methods.

Thank you! I was just about to use this foam to set a 10-foot gate post!

Thank you so much for doing this. Saved me time and money.🇨🇦

Thanks for the heads up!

I used this for My mail box post, all I can say is WOW and WOW Very solid and strong

Very illustrative, thank you for sharing

Thank you for the video. When I used the foam, I poured it against the fence post and above ground level. That way the foam will coat the post and seal it against water. (It will slide down the post and you won't get that rolling effect that you see in the video.) I also went back a couple of days later with a utility knife (any knife would do) and trimmed the above-ground foam away from the post at an angle.) Finally, I think the bags cost me between $6 and $9. If you are digging a wide hole, consider getting two bags. At my age, it's a lot cheaper than a strained back! Thank you again and no, I don't work for them!

so glad you did this vid!

Thank you! You've made our mind up.

I have used foam in situations as a tech in telecom. I know how it works. One of the issues I have with using it to set posts is the weight that concrete adds to help with creating a lower center of gravity and a "foundation" for the fence. Especially is this crucial on gate posts. The extra weight of the swinging gates will inevitably cause those posts to lean.

Very Helpful! Thank you!

very helpful! thank you from milwaukee! i am installing a hefty modern mailbox and was wondering and this helped loads lol

My dad was an engineer and volunteered my brother and I to work with him in a family business, materials and welding engineering. We had a piece of equipment which had a plaque that had a statement, "one test is worth ten thousand expert opinions". Thats for the quality test.👍

Good to know. Thanks!

THANK YOU FOR THIS!!!

I was considering using the foam for a project this summer.. Sticking with concrete after this video. Thank you!!

i went 4 ft or 1.22m deep and used a 1.5 bags/hole, 1 set bag and .5 bag later as filler. make some sort of plastic cone (oil it) for the overflow, this will provide some downward pressure as the foam expands and help resolve the water issues mentioned. Both methods would be a lot stronger filled to the top too

I had the ultimate test of fence posts set in concrete. During Hurricane Katrina in Mississippi, USA, posts broke off just above the concrete. Some posts shifted and others snapped laying about 25' down, sheered where the nails failed. I am a firm believer in concrete, though a pain to replace, but very sturdy. I am also a firm believer is using screws instead of nails as screws do not pull out unless they break.