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Replacing wood fence posts at the same location continued...
2

Replacing wood fence posts at the same location continued...

Replacing wood fence posts at the same location continued...

(OP)
thread194-495078: Replacing wood fence posts at the same location

This is a continuation of a previous thread (now closed) on solution to replace a wood fence post 4X4 or 6X6 at the same location. I have resolved the issue, somewhat but like to get some feedback, in addition, I like to reply to some of the previous suggestions.

The issue at hand is when you have to replace a wood post due to damage or rot, and said post was previous set in concrete, which is required by code where I am), how do you avoid the post hole getting bigger and bigger with each "iteration"?

With a regular fence post most just cut off the bad post, and dig a new hole say a foot over, and shift all the posts along the fence line, this avoids having to dig up the old concrete, and the digging of the new hole in regular soil is much easier, but in the case of a gate post, it has to be in the same exact spots, and if you are replacing the posts say every 10 years (due to termites, moisture penetration etc...) each time the crater gets bigger and bigger, from 8" to 12" to 16" to 22" etc...I have one 6X6 posts I pulled out and the hole from the concrete anchor and the digging around it is in excess of 24" in diameter.

Obviously, the easiest solution is to just put in as much concrete is needed to fill the bigger hole. In this case cost is not a concern, I just want to get back to a normal sized hole that's workable.

One thing I did try, and that is to backfill the entire hole with the same dirt, compact as much as possible, then dig a new hole into the backfilled soil, that doesn't work. The newly compacted soil does not stay firm enough. I did an experiment. Dug a 14" post hole 24" deep. Then backfilled that hole with the excavated dirt, compact by hand and also add water to help compaction. Waited one week of time, then in the backfilled area dug a smaller 8" hole 24" deep. I also dug a new 8" hole 24" deep only 2 feet away, at a location that has never been backfilled. Once dug, I jumped up and down near both holes. The result is the soil in the backfilled hole collapsed and caved, where the other hole has no such issue.

Out of all the solutions proposed, there was a suggestion to brace in sonotube into the large hole, fill it with concrete and post, then when set, backfill the soil around the sonotube and compact. That may have worked but I never tried it, I may one day.

The other suggestion was instead of digging out the post and concrete anchor, hire a core drilling company that can drill say an 8" hole 24" deep, to just drill a fresh hole in the concrete, keeping most of the old concrete in the ground. This also may work. In fact I may try this very soon with a set of six wrought iron fence posts I have at another location.

What I end up doing in this particular case, was I spoke to a local old time mason about this issue, and he suggested a method. What he suggested was after I dug out the old concrete, and have this big crater 24" or so deep, 24" in diameter, instead of backfilling with regular soil, or fill the entire crater with concrete, I could use Portland cement. So basically I bought an 80 pound bag of Type II Portland cement, and used the entire bag to mix with a wheel barrow full of regular soil/sand. Once mixed, I backfilled the hole, compact and wet it with water. Left it alone for e few days. then excavate a new hole. I did that and did the same jumping up and down near the hole and there was no collapsing of the soil. The new backfill feels a bit stiff but still can be excavated with a regular shovel or post hole digger fairly easily. That's what I end up doing and set the posts, so far it has been fine, no leaning, no setting with the two 5' gates.

My question is, by mixing the Portland cement and soil (no other additive, no aggregates, no line), what has happened to the soil? It seems to be more stable but is it really?

RE: Replacing wood fence posts at the same location continued...

Is there a reason you cannot approach the AHJ to see if you can set them in compacted granular material? Properly done, they will be just as solid and will be less prone to rotting off. If necessary, can you obtain a variance or something like that?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Replacing wood fence posts at the same location continued...

When you backfill a hole you have do it in stages (lifts).
For a 18" diameter hole fill maybe 8-10" at a time and compact, then fill the next, and so on.
You soil must be nearly all sand, correct?
You really need to use posts that the bugs won't eat and that won't rot.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Replacing wood fence posts at the same location continued...

What you have done is called cement stabilization. Usually about an 8:1 ration of soil to cement. Common in road building for subbase lifts.

RE: Replacing wood fence posts at the same location continued...

The answer is: do not bury the post in concrete. Rather embed a metal post base in the concrete. Then install the post on the base.

RE: Replacing wood fence posts at the same location continued...

(OP)
"When you backfill a hole you have do it in stages (lifts).
For a 18" diameter hole fill maybe 8-10" at a time and compact, then fill the next, and so on.
You soil must be nearly all sand, correct?
You really need to use posts that the bugs won't eat and that won't rot."

Yes soil is very sandy. Probably about 6 to 8 inches of top soil, then mostly sand below that. If I dig down 28" or so, I see water. I am very close to the river and 3 miles from the ocean, and so below 26" it's constantly wet.

I did compact in stages, every 3" or so backfilled I hand compacted then wet it down.

I am trying to use less rot prone materials, but it's difficult where I am because being in a historic district I am limited to natural materials. No PVC, no metal, no cement based materials (although they started to allow cement board sidings if they look like wood sidings). However, instead of using the conventional ground contact pressure treated 4X4 posts, I ordered from a marine deck and docks place locally CCA treated .6 lumber instead of the ACQ treated lumber sold at regular lumber yards, at about 5X the cost. The issue which I did not anticipate, is this much longer lasting treatment with copper is very corrosive to modern day fasteners, so if I want to fasten rails and pickets to it, the regular ceramic coated deck screws or galvanized nails rated for ACQ lumber may not last long on them. I end up using stainless steel fasteners but will see what happens. The only lumber I can buy that is even more rot resistant are the round 20" diameter pilings used for marine construction and power poles.

RE: Replacing wood fence posts at the same location continued...

(OP)
"What you have done is called cement stabilization. Usually about an 8:1 ration of soil to cement. Common in road building for subbase lifts."

I have no idea what kind of ratio I used or even if it's sound except for my quick experiment it did seem like it worked. I will keep the 8:1 ratio in mind. I am surprised that no lime was needed, I thought for Portland cement to work chemically that lime had to be added.

RE: Replacing wood fence posts at the same location continued...

(OP)
"The answer is: do not bury the post in concrete. Rather embed a metal post base in the concrete. Then install the post on the base."

Local code requires posts embedded in concrete. I see what you are suggesting is if allowed, I can keep the concrete base and keep changing out the post base when it gets completely rusted. However it will not pass inspection for Florida fences.

By the way I do have metal posts with wrought iron fence panels in another side of the same property. Right now I am in negotiation with the city to allow me to replace it with the same fence, the negotiation is due to metal fences are no longer allowed but I am arguing this is a "repair". If they let me do it all these posts deeply buried in concrete I plan to just cut them at the ground level, then hire a concrete cutting company to come drill an 8" hole down 24" deep to remove the old posts, then install new posts with new concrete, weld the old fence panels back on.

RE: Replacing wood fence posts at the same location continued...

Your solution is essentially what one of the previous posters suggested in the first thread - use CLSM (controlled low-strength material) which is essentially a very weak concrete due to the small quantities of portland cement). Concrete is water, cement, and aggregate (aggregate usually consists of both fine and course, so sand and gravel). You made concrete, only your aggregate is whatever the native soil is made up of.

Lime is definitely not required - it is often used when mixing mortar to make it more flexible.

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