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.

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.

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

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!

Thanks for the heads up!

I've installed many field entrance posts with 16-20' steel gates. I've used concrete and foam more recently. I would never go back to concrete. The foam is easy to work with and if done correctly, it protects the post and is every bit as stable.

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

If you add the foam correctly, its a much better seal against water. When you add the foam liquid you are supposed to make sure you pour it against the post on all four sides so that the post is coated with foam liquid even above grade. Also, lets fill the hole...lol..the foam should come above grade. We use a product by a different name (Fast2K), and its far superior to concrete.

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

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.👍

Up here in wet rainy Oregon, some of us use Pea Gravel for the post. It helps a few ways, like if the post moves even a fraction in the wind the gravel sinks and tightens the post continually never letting the post get loose. (Just keep the pea gravel capped off). Also, the water has a drain away from the post ground level so the water rot in that spot is no longer a problem. Another way it helps is that there is no concrete mixing! Many up here think it's faster and better.

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

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

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

Being American- I cannot comment on UK soil conditions. But here in the north east USA I dug a 36" post hole and used Post Fixit with a 4x4 post like you used. I mounted a substantial retractable hose reel that weighs about 40 Lbs. 3 years later, it has held with no noticeable tilting. You perhaps should have dug a deeper hole than you did. And yes, where I live we do have a high water table, but I make sure I tripe sealed my pressure treated post with deck seal-, paint, and a plastic moisture layer. I hope this helps.

Very illustrative, thank you for sharing

Thank you! You've made our mind up.

Very Helpful! Thank you!

I used the foam product on two treated 6 ft posts and it worked great and both posts are totally solid. I used a post hole digger and that left a hole just a little larger than the post. The mix in both cased grew just slightly above ground level.