What are you guys doing for backfill after the posts are set on the footers? I know you want something that compacts well but what is best to keep moisture to a minimum on the buried part of the post? I assume topsoil is not the best option so is fill dirt the best option or stone? How about recycled asphalt because it compacts well? I was told in another post the reason not to use recycled asphalt under the slab would be possible smell and that seems like good advice but how would it work for the posts?
Backfill for pole barn posts???
- Thread starter Jay13
- Start date
did you strip all the top soil off from the building area before drilling your post holes?
hopefully your holes were drilled into some nice hard clay, if so use that to pack around your posts. you want no air on the part of the post that is in the ground and no water on the part of the post above the ground... water+air+wood= rot
usually you want to use the same stuff that came out of the hole to refill the hole.
NO TOPSOIL in the hole or under the slab
best practice is to grade so that you have fall away from your building in all directions, and to make the floor of your pole barn the highest part of grade.
hopefully your holes were drilled into some nice hard clay, if so use that to pack around your posts. you want no air on the part of the post that is in the ground and no water on the part of the post above the ground... water+air+wood= rot
usually you want to use the same stuff that came out of the hole to refill the hole.
NO TOPSOIL in the hole or under the slab
best practice is to grade so that you have fall away from your building in all directions, and to make the floor of your pole barn the highest part of grade.
rburke65
Well-known member
Concrete "cookies" under the posts, but I think I would use a "gravel" or stone that would compact and provide drainage.
oh and if you're thinking of using concrete... your wood post will shrink a little and the concrete will shrink a little... those two little bits of shrinking will make just enough room for air around the moist wood post that is in the ground, not saying it will make it rot but if will make perfect conditions for it.
I haven't started the build yet, its far to wet to even think about stripping the topsoil off right now. I am just trying to get input on backfilling the holes. I understand why you never incase the posts in concrete, I have to pour 22"w x 11"d footers in the holes per code to set the posts on but am unclear about what to refill the holes with. I plan on bringing in enough fill to have the floor 6-8" above grade and slope everything away on the outside also.
olytdi
Well-known member
The last thing you want around your posts is gravel. It will be where water congregates. It's why you use gravel with drain pipe -- it pools.
There are post sleeves that you can get to isolate the wood from the fill. Then use fill that isn't prone to holding water -- higher clay content.
There are post sleeves that you can get to isolate the wood from the fill. Then use fill that isn't prone to holding water -- higher clay content.
Firebrick43
Well-known member
Whaaaat!
Gravel is porous and allows for water to quickly flow through it and drain away. If water pools in gravel it's not the gravel but the lack of a drain path and more than likely a fine soil such as clay that prevents water from draining. Just because you don't see puddled water in soils doesn't mean the water is not there, it's absorbed into the soil and takes longer to dry out than gravel. The gravel (crushed and washed without fines) allows airflow drys out faster. Soils contain microbes that promote rot, gravel/crushed stone has much less due to the lack of organic food.
Don't believe me? Take two glass bowls and fill them half full, one with soil, the other gravel. Add a cup of water to each. Sure you can see the water "pool" in the bowl with gravel and can't in the one with soil. It's the bowl that holds the water in. Now dump both out. The water runs instantly away where the soil one will hold on to it for a long time. If you don't dump them out the gravel bowl will dry out first(checked by weight).
There is good reason that crushed stone is the prefered sub base the world over.
If you put proper drainage around the structure as it should have then water is not a problem in either stone or native soils.
theoldwizard1
Well-known member
concur !!
go to the hobby shop and get some modeling clay.
make 3 finger sized holes in the clay
put a wood chop stick in the center of each hole
this would replicate your wood posts in the hole.
in hole #1 with a chop stick in it, leave empty (no fill)
in hole #2 return clay to surround chop stick (clay fill)
in hole #3 fill with BB's to surround chop stick (gravel fill)
now take your model to the sink (or outside) and pour water over top to simulate rain
observe which holes performed best
make 3 finger sized holes in the clay
put a wood chop stick in the center of each hole
this would replicate your wood posts in the hole.
in hole #1 with a chop stick in it, leave empty (no fill)
in hole #2 return clay to surround chop stick (clay fill)
in hole #3 fill with BB's to surround chop stick (gravel fill)
now take your model to the sink (or outside) and pour water over top to simulate rain
observe which holes performed best
Dig a hole and fill it with gravel. It will hold water. Dig a hole and fill it with compacted soil and it will not.
Someone posted this a while back. Good info.
http://www.pole-barn.info/post-foundation-embedment.html
Firebrick43
Well-known member
Modeling clay is nearly impervious to water, so you formed a bowl. What did you prove? Take a bamboo skewer and poke a hole it in the side so it touches the vertical "post" hole simulating a proper drainage tile, now how does your test perform? Does everyone have clay soils the consistantcy of modeling clay that will absorb very little water?
Did you even read my post? Just because you can see water in a gravel filled hole and "can't" in a soil filled hole does not mean it's not there. Heard of mud? Have not seen a native soil yet that doesn't hold and absorb large amounts of water.
And your link suggest pouring concrete around wood, no faster way of rotting out a post.
Sure there is, backfilling with gravel.
Firebrick43
Well-known member
Glad you came along and made sure we don't follow what thousands of professionals and all those ignorant building science guys have said for years.
http://www2.iccsafe.org/states/newjersey/nj_residential/pdfs/nj_res_chapter4.pdf
Page number 59 & 60. Guess those international code council guys are ignorant as well.?
Just the first hit googling "crushed stone foundation drainage pdf"
pcmeiners
Well-known member
Clay or gravel? With the treated wood we get nowadays, I trust neither. Reinforced concrete piers made with sonotubes to save on concrete, then fill the rest of the holes with gravel which gives a stiff base, more so then clay. Wood remains above ground, no rot, makes it harder for termites.
Apples and oranges. Yes gravel is good for drainage but what about when the water has no where to go, like in a hole, it will collect. For wood to rot you need water and air. Gravel is good at providing both because of all of the voids.
I built a 50x72 about two years ago. Talked with many builders. No one used gravel. The standard was a precast concrete cookie to keep the post seated. Ears on the post for uplift, a 80# bag of dry mix then compacted dirt for backfill. Only other variations were companies like Morton that offer precast piers etc. Do a search on here and hear from others that actually build as to the way they do it. Here's one to start with:
http://www.garagejournal.com/forum/showthread.php?t=12849
Regarding setting in concrete, in some areas code requires it on barns that have open sides to handle the uplift.
Either way if they are buried in the ground they usually rot right at the surface first anyway.
Firebrick43
Well-known member
Permacolumns are great, no argument there, had them since 2001 when they were not well known.
I fail why anyone would not provide proper drainage for any building built in any manner? Especially clay soils or soils with high organic matter will expand and contract as they become wet and dry. Seen post jacked right out of the ground, especially with concrete cast around them. Concrete floors cracked and buckled as bare wet clay expands/contracts. Put gravel down and provide drainage and no expansion can happen nor frost heaving.
It's also easy to dig the holes a foot or two deeper, back fill hole same amount with gravel and tamp, then set your cookie/post.
When greater uplift resistance is required you can use uplift anchors instead of concrete, they make ones that are engineered to the job.
Many builders do things wrong out of ignorance or being beaten down on "lowest price". Doesn't make it right. Crushed gravel means extra cost to haul it in, move it on site, and move away the dirt dug out of the holes.
Dumping a dry bag of concrete is silly. No control at all. Most pole builders don't put 8"+ gravel under the slab(or none), pour concrete with to high of slump, and try to pull the wire up while standing on it to. Most don't isolate the slab from the post either.
I wish I could go this route but code won't permit the posts to just be anchored to piers. The posts must be 48" beneath finish grade sitting on 22"w x 11" thick piers.
lakeroadster
Well-known member
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olytdi
Well-known member
How are you going to install drains from the gravel you filled your post holes with?
Also, if you use sleeves on the posts underground, you insulate the wood from dampness.
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