I am about to start building my 30'x27' pole garage. I planned to backfill my holes with the dirt that I removed from the holes. After digging my holes I found out that my ground is almost solid clay. Is it a bad idea to back fill my posts with the clay filled dirt that I removed from my holes? I am guessing the clay is not good for drainage? Thanks for any info.
Backfilling post with clay
- Thread starter blair683
- Start date
Orionrising
Well-known member
clay effectively does not drain.
adam0872
Active member
You need to backfill with top soil
OccupantRJ
Well-known member
I backfill posts with sand. It tamps in well and tightens posts up rock solid.
padroo
Well-known member
Sand is best because it settles the fastest, just add water.
Captain Spaulding
Well-known member
I have never seen anybody not set them in concrete. Seems crazy to fill the holes with anything else because the soil lateral bracing is critical to the structure of a pole building.
ishiboo
Well-known member
I think the minimum would be set on concrete cookies, and filled with gravel.
theoldwizard1
Well-known member
Either of these 2 or both is common and good practice. Sand "drains" well. Gravel (not rounded) even better. Both will settle and be almost as strong as concrete.
The biggest problem with using concrete is that you typically will get a small gap between the concrete and the post. Water will infiltrate. Even PT posts don't do well siting in water. Freezing can also cause the concrete to crack.
lakeroadster
Well-known member
I built a barn back in Ohio in the early 1990's.. clay seems to be the norm.
In answer to your question: Backfill with the material that came out when you dug the holes.
Think about this for a minute...
- If you've dug holes into clay soil for your columns, and it is truly clay, and then you fill the hole with gravel, it will be like a big plastic container full of gravel that will hold water. You've built a sump.... and that's not at all what you want
Back filling with whatever was there originally means it will drain the same as it did before you installed the columns.
Make sure the building is higher than the surrounding elevation, and make sure your finish grading has a slope away from the building. And be sure to add gutters and downspouts that shoot the water away from the building. Do that and it'll be fine.
You didn't ask about the concrete "cookie" concept in the bottom of the hole... but it is a good idea... it helps distribute the downward force over a larger area and minimizes the chance of the column sinking into the soil.
Thanks guys. I already bought the premade concrete cookies for the bottom of the holes. Waiting now for the excavating company to get here to do the holes. I also have an 80 lb bag of quickrete for each hole. Going to pour one bag dry in the bottom around each post. I like reading about everyone's opinions and ideas about the different methods and materials. It gives me options that I never would have thought of on my own.
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Captain Spaulding
Well-known member
What will keep the building from lifting in a high wind?
if we get enough wind to pull sixteen 6"x6" posts with 15 trusses sitting on them out of the ground. Then this building will be the least of my worries. There is tons of mobile homes and campers in this crappy trailer park across town. None of them are anchored to the ground and have been sitting there for 30 years. I think my 6"x6" posts burried four feet in the ground will be alright. I am also pouring an 80lb bag of dry quickrete in the bottom of the holes after the posts are set.
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theoldwizard1
Well-known member
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lakeroadster
Well-known member
Typically each post will have (2) 2x6's attached to their faces at the bottom of each column. This locks into the fill dirt. This is the method most of the pole barn manufacturers (Morton, Lester, etc) use to prevent lift.
You can see the 2x6's in this photo....
Drain where? The bottom of the hole also is clay. The drilled hole is like a big clay tube. The more water that is held, the longer it will take to drain.
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mrobins297aaa
Well-known member
I agree makes a lot of sense.
instead of using the concrete cookies in the bottom of the holes, I like the idea of just mixing up 2 bags of ready mix in a wheel barrel (make it soupy) and pouring it into the holes. It will be self leveling and your assured of complete ground contact on the bottom side. I don't know how you can be sure of that with the concrete cookies.
Hephaestus29
Well-known member
I definitely would NOT use top soil
as suggested above, especially if it's
going to be for your pole barn.
Top soil doesn't really compact like
you need a filler to do in an area like
that. I have heard of pea gravel being
used but as far as compaction goes ?
People in the south have a lot of
clay/sandy soil, if thats what it is you
should be fine. If it's just clay ???
as suggested above, especially if it's
going to be for your pole barn.
Top soil doesn't really compact like
you need a filler to do in an area like
that. I have heard of pea gravel being
used but as far as compaction goes ?
People in the south have a lot of
clay/sandy soil, if thats what it is you
should be fine. If it's just clay ???
LX-Markham
Well-known member
I have no opinion to offer on the backfill, except to agree with the above: do not use top soil.
But I have to ask: what is a concrete cookie?
Have never heard that term up here.
But I have to ask: what is a concrete cookie?
Have never heard that term up here.
rburke65
Well-known member
Concrete is a round precast concrete shaped "cookie" that is placed in the bottom of the drilled/dug post hole which acts as a footer for the "pole" of the pole barn structure. I would vote for the clay soil for a backfill.
myredracer
Well-known member
I've always understood that if using concrete around a post the the bottom of the post should not sit on concrete. Concrete should extend above the grade level and be sloped away from the post. If backfilling with clay, it should also be sloped away from the posts. If using gravel, can use clay or concrete at the grade level that is sloped away. A problem with concrete is that it can shrink and allow water in around the posts and caulking can be used to seal the gaps.
They usually don't rot much below grade because of a lack of oxygen for the bacteria, microbes and fungus that cause rot. Posts usually tend to break off at the ground level because that's where they stay wet for prolonged periods and have a source of oxygen. Doesn't matter much if you backfill with clay, gravel or concrete if oxygen can't get down to the wood to rot. Creosote, if you can still get it, would help somewhat. Posts won't last no matter what you do unless you're in a really dry climate. Western Red cedar will be 2nd growth or later and doesn't resist decay like 1st growth does. Best post is concrete and post saddle or steel set in concrete.
I installed 1500' of farm fencing around perimeter of our property. Since we have a high water table for a prolonged period and the soil is clay down all the way to China, I thought it would be smart to use 3/4" clear crushed gravel around the posts. Holes were all done with a 12" auger so a min. amount of gravel was needed. Posts were pressure-treated 4x4 (pine IIRC). Couple of years later I leaned against a post and it snapped - right at ground level. I did not put clay at the ground level and in retrospect I guess I should have. I'd use native clay the next time.
They usually don't rot much below grade because of a lack of oxygen for the bacteria, microbes and fungus that cause rot. Posts usually tend to break off at the ground level because that's where they stay wet for prolonged periods and have a source of oxygen. Doesn't matter much if you backfill with clay, gravel or concrete if oxygen can't get down to the wood to rot. Creosote, if you can still get it, would help somewhat. Posts won't last no matter what you do unless you're in a really dry climate. Western Red cedar will be 2nd growth or later and doesn't resist decay like 1st growth does. Best post is concrete and post saddle or steel set in concrete.
I installed 1500' of farm fencing around perimeter of our property. Since we have a high water table for a prolonged period and the soil is clay down all the way to China, I thought it would be smart to use 3/4" clear crushed gravel around the posts. Holes were all done with a 12" auger so a min. amount of gravel was needed. Posts were pressure-treated 4x4 (pine IIRC). Couple of years later I leaned against a post and it snapped - right at ground level. I did not put clay at the ground level and in retrospect I guess I should have. I'd use native clay the next time.
redmondjp
Well-known member
I, too, live where we have clay. I recycled true 4x4" old-growth cedar fenceposts from the neighbor's 1977-built fence a few years back, that were backfilled with the native soil. It sealed up the wood and there was zero rot up against where the clay soil contacted the wood (my theory - the oxygen was prevented from getting into the area, preventing most microbial growth).
lakeroadster
Well-known member
We used a combination of footers and concrete "pucks". Pucks were only used on columns that did not support trusses. All the 4ply truss support columns had 12" thick footers. Here's a photo...
30" Footer and 17" Puck
