Barn project - setting concrete piers

[EddieWalker]

My initial question is still relevant though, and I can see now how the posts can be set precisely in line so that everything comes out plum and square. The drainage issue is probably the best advice I have seen regarding wood piers. I plan to backfill the holes with crushed stone or gravel and landscape so that water will run away from the posts and not collect at the base. I'm still not clear though on whether a concrete footing is appropriate. My thinking is that perhaps I would be better off with six or eight inches of large stone (maybe 1 1/2") at the bottom of the hole. This would allow moisture to percolate down and away from the end grain of the posts.

To get everything lined up, do your corners first. Get them set and then leave the rest of your posts loose in the holes. Once you attach your purlins, you can straighten out our posts. You might have to take a few posts out and redig, but that's just physical labor.

Do not backfill with gravel or stone. I've read that you need gravel at the bottom of the hole, and I've read that there should be something solid at the bottom of the hole. I don't see what it hurts to do this, but don't think it accomplishes anything. With gravel at the bottom, it might actually hold moisture and create a wet area at the bottom of the post. You want the backfill to be clay or concrete. If its sand, then use concrete. If its loam or anything that holds water, use concrete. The idea is to lock the post into the hole. The surface area of the sides of the post are what give you all your strength. The actual footprint of the post, or the bottom of the post, doesn't actually carry much of the weight of the building. If it did, it would sink. Get the posts tight in the hole and you will never have a problem. If you use gravel, not only will the post not be tight in the hole, you will actually create an area that will hold water. Gravel and sand are the two very worse things to put in a hole with a post!!!

Eddie

 

[Red Horse]

Most pole barn building companies use 16" concrete donuts at the bottom of the hole as a footing. In my area it is code. You may not be subject to code but to me there is no reason to out guess the engineers at the pole barn companies.

MarkV

This is a variation on your method. Precast concrete footings formed using cut plastic 55's as forms. When these are poured, galvanized straps are cast in. The square OSB board that sits on the concrete is a sacrificial piece that has a hole cut in it that matches the post dimension. Then when these short posts are "squared" off, the galvanized straps are then nailed to the OSB blocks These blocks keep the posts from kicking out during backfill. These short PT posts extend a reasonable amount above grade then the non-pt posts are added supported by the "sistered" 2 x ? pieces.

 

[schweizer]

There are lots of opinions on how to set posts for a pole barn. The consensus is that the posts don't rot deep in the bottom of the hole, even if there is water or poor drainage, or encased in concrete, etc. The posts rot at ground-air interface level, and only when they are wet. Dry pressure treated posts should last a long time. Encase them in concrete and keep water away from the ground level (i.e. slope away from building) and they should last a long time.

I just started a 36' x 36' pole barn last week. The concrete for the posts was just poured yesterday. Around here they dig 4' deep w/ an auger, and clean out the hole of loose dirt. Then they pour a 90 lb bag of dry concrete mix into the bottom of the hole and set the pole on top. Then you get all the poles plumb and straight using batter boards and string lines. Concrete was poured to the very top on all my posts, and I crowned up the concrete around the posts so that any water will run away from the base of the post. Next, I'll bring in about 6 inches of gravel, and level it in the barn and slope away from the site. Then I'll be ready to continue w/ girts, etc.

Here's the thread I started on it (not updated for yesterdays concrete yet):
http://www.tractorbynet.com/forums/build-yourself/244220-building-old-fashioned-appearance-new.html

 

[EddieWalker]

This is a variation on your method. Precast concrete footings formed using cut plastic 55's as forms. When these are poured, galvanized straps are cast in. The square OSB board that sits on the concrete is a sacrificial piece that has a hole cut in it that matches the post dimension. Then when these short posts are "squared" off, the galvanized straps are then nailed to the OSB blocks These blocks keep the posts from kicking out during backfill. These short PT posts extend a reasonable amount above grade then the non-pt posts are added supported by the "sistered" 2 x ? pieces.

I don't understand this at all. What is the beifit of pouring concrete below grade and then having a post come up the rest of the distance, but ending above grade?

For what it cost to do it this way, why didn't you just put 4x6's or 6x6 posts in the hole and build from the biggest, most solid post you could use?

Is this a barn that you are building or some other type of structure?

Eddie

 

[mattbatson]

I don't understand this at all. What is the beifit of pouring concrete below grade and then having a post come up the rest of the distance, but ending above grade?

For what it cost to do it this way, why didn't you just put 4x6's or 6x6 posts in the hole and build from the biggest, most solid post you could use?

Is this a barn that you are building or some other type of structure?

Eddie

Mr. Eddie, I just want to thank you and some others on here for helping me plan my crawlspace foundation that I will be building (I'll be bolting a quonset hut on top of it).
I had planned on pouring concrete piers and all of that other stuff, when as it turns out, it would all be mostly a waste of time and money.

So, just to make it all perfectly clear and to sum it all up...

1. The posts get their strength from the friction of well tamped soil surrounding them...
2. regular native soil under the bottom of the posts....no concrete or gravel
3. Concrete doesnt seem to be needed at all


I had heard in the past that when surrounding a wood post in concrete, that the concrete will pass water to the wood and rot it over time? Might be false, I dont know...

One more quick question...
I know that you can buy this "fence post paint" from tractor supply that looks like black tar. I was thinking of painting this onto the posts from their bottoms all the way up to about a foot above grade?
Think it is worth it?

 

[EddieWalker]

Concrete doesn't hurt anything and if your have loose soil, such as sand or loam, then it really adds strength to the post. I don't believer there is an issue of moisture coming through the concrete or down the concrete to the wood. All your rot and decay happens at ground level. Concret or not, the post will look brand new in the ground 30 years from now, but if you don't get rid of the water, the very best PT wood will rot out in ten years or less at ground level.

Fence paint isn't going to add anything. In my opinion, it's a waste of money.

Eddie

 

[dustinfox]

The pouring of concrete around posts is getting confusing. There is no shortage of opinions that concrete absorbs moisture and that wood posts in direct contact will act like a wick absorbing the moisture. But there are just as many who say the benefits of providing a footing, as well as locking the poles in place, make concrete indispensable. It seems there are pros and cons to each method. Guess I need to do more research.

 

[MotorSeven]

Eddie, why would gravel at the bottom of a post hole hold more water or moisture than the soil it's stitting in? French drains, and gravel field lines have been used for hundreds of years to let water move through the gravel and disperse in to the soil. I still think gravel is more beneficial in this application than nothing at all....just my opinion. I think we are all right about water and drainage away from any post...standing water will kill any post every time and do it quickly.

 

[Red Horse]

I don't understand this at all. What is the beifit of pouring concrete below grade and then having a post come up the rest of the distance, but ending above grade?

The concrete is not poured. these are precast. benefit is you get approximately 700 sq. inches of bearing surface vs say 36 if you use a 6 x 6 post.

For what it cost to do it this way, why didn't you just put 4x6's or 6x6 posts in the hole and build from the biggest, most solid post you could use?

Is this a barn that you are building or some other type of structure?

Eddie

this is a cost effective alternative vs. using pine posts or PT posts that are full length.

This is a barn that was built at our fairgrounds by one of the larger barn builders in this part of New England. And this thing is SQUARE!

I agree on the risks of water-"keep it high, keep it dry". I myself am not a fan of non -pt in the ground.

One other point- I believe the comment was made.."okay to set in native soil"- to add to that. NEVER set anything on ground that has been disturbed-in other words -never put "dirt"-back in the hole. That is the benefit of using crushed stone in the bottom as the "leveler".

 

[EddieWalker]

Eddie, why would gravel at the bottom of a post hole hold more water or moisture than the soil it's stitting in? French drains, and gravel field lines have been used for hundreds of years to let water move through the gravel and disperse in to the soil. I still think gravel is more beneficial in this application than nothing at all....just my opinion. I think we are all right about water and drainage away from any post...standing water will kill any post every time and do it quickly.

Kind of hard to compare a french drain with a hole in the ground that doesn't go anywhere.

Leech fields rely on the soil perculating, or absorbing the fluids in the lines. Depending on the soil, this might take a trench 100 feet long, or 300 feet long. It depends on the surface area and how well the soil absorbs moisture. This is also a very shallow trench designed to get the water to soak into the ground.

The reason a post rots out is moisture. Mostly the getting wet and drying out procces. This is why posts rot out at the surface, because the area around the post settles and becomes a bowl. If you can built up the soil or concrete around the post, it will shed water and in theory, last it maximum lifespan.

While I cant say that gravel at the bottom of the hole will hold enough water to cause any issues, I don't see where it will help anything. I think somebody got an idea that this will lead to allowing water to drain away from the post faster, but forgot that 3 feet down or more, the ground doesn't perk worth a darn and any water that gets in that hole, stays in that hole. Giving it more space to stay longer doesn't make any sense to me.

Eddie

 

[dustinfox]

Kind of hard to compare a french drain with a hole in the ground that doesn't go anywhere.

Leech fields rely on the soil perculating, or absorbing the fluids in the lines. Depending on the soil, this might take a trench 100 feet long, or 300 feet long. It depends on the surface area and how well the soil absorbs moisture. This is also a very shallow trench designed to get the water to soak into the ground.

The reason a post rots out is moisture. Mostly the getting wet and drying out procces. This is why posts rot out at the surface, because the area around the post settles and becomes a bowl. If you can built up the soil or concrete around the post, it will shed water and in theory, last it maximum lifespan.

While I cant say that gravel at the bottom of the hole will hold enough water to cause any issues, I don't see where it will help anything. I think somebody got an idea that this will lead to allowing water to drain away from the post faster, but forgot that 3 feet down or more, the ground doesn't perk worth a darn and any water that gets in that hole, stays in that hole. Giving it more space to stay longer doesn't make any sense to me.

Eddie

Thanks again Eddie for your helpful and valuable input. I understand what you are saying. If this is the case then, from a moisture control perspective, it makes no difference what you put at the bottom of the hole because it is the native soil below which will determine how much moisture collects at the bottom. I have to believe though, that stone would not absorb moisture the way that concrete would. I only need to look at the floor in my garage on a humid day to see how the concrete absorbs moisture. Perhaps a large flat rock would be a better alternative for stability.

 

[SHORT KID]

All of these ideas are confusing, but have merit for the praticular areas. What I look at is the utility poles, some of them have been in the ground for ever. The utility company digs around them periodicaly to check for rot or termites. I have seen pole barns done like this 40 or more years ago that are still sound, but have good drainage around them. They were backfilled with the original surrounding material. We all like things to last, but nothing lasts forever, maybe if they were made out of recycled plastic or vinyl!!! :laughing::laughing:

 

[dustinfox]

All of these ideas are confusing, but have merit for the praticular areas. What I look at is the utility poles, some of them have been in the ground for ever. The utility company digs around them periodicaly to check for rot or termites. I have seen pole barns done like this 40 or more years ago that are still sound, but have good drainage around them. They were backfilled with the original surrounding material. We all like things to last, but nothing lasts forever, maybe if they were made out of recycled plastic or vinyl!!! :laughing::laughing:

I think the utility companies may still have access to creosote. The government, in its great wisdom, has decided that us consumers are to irresponsible to be trusted with it.

 

[EddieWalker]

Thanks again Eddie for your helpful and valuable input. I understand what you are saying. If this is the case then, from a moisture control perspective, it makes no difference what you put at the bottom of the hole because it is the native soil below which will determine how much moisture collects at the bottom. I have to believe though, that stone would not absorb moisture the way that concrete would. I only need to look at the floor in my garage on a humid day to see how the concrete absorbs moisture. Perhaps a large flat rock would be a better alternative for stability.

You are comparing apples to oranges.

The moisture you see on your concrete is condensation and it comes from the changing air temperature inside your building. It isn't that the concrete is absorbing the moisture, it's that the temperature of the concrete is cooler then what the moisture in the air can hold, at the concrete. Exact same thing that happens to a cold soda can on a hot day. The air next to the can cools and the moisture in the air becomes solid and forms on the can. Water goes from a gas to a liquid.

Inside the hole, the theory is that the gravel keeps the post off of any water that gets to the bottom of the hole and allows the end of the post to remain dry. This is a theory. Not something that I'm aware of that has ever been proven. "My" theory is that if any water gets to the bottom of the hole and there is gravel in there, it will hold the moisture longer then if there wasn't a place for it to go. Make the bottom of the hole solid and water wont be drawn to it or have a place to stay.

With poles, I think simple is better. There isn't any advantage or proven reasoning to over thinking it or putting extra money into it. Buy quality PT poles and dig your hole deep enough to avoid frost heave if that's a concern where you live. Back fill and compact with the dirt that came out if it's compactable, or use concrete if you are in sand or loam. Slope the top of the fill and keep the post dry.

Anything more just doesn't have the proof out there that it helps anything, and in some cases, it might hurt.

Eddie

 

[dustinfox]

You are comparing apples to oranges.

The moisture you see on your concrete is condensation and it comes from the changing air temperature inside your building. It isn't that the concrete is absorbing the moisture, it's that the temperature of the concrete is cooler then what the moisture in the air can hold, at the concrete. Exact same thing that happens to a cold soda can on a hot day. The air next to the can cools and the moisture in the air becomes solid and forms on the can. Water goes from a gas to a liquid.

Well yes but in the case of the concrete, the condensed moisture is absorbed and does not sit on the surface like on a soda can. The concrete acts like a sponge.

 

[GLyford]

Inside the hole, the theory is that the gravel keeps the post off of any water that gets to the bottom of the hole and allows the end of the post to remain dry. This is a theory. Not something that I'm aware of that has ever been proven. "My" theory is that if any water gets to the bottom of the hole and there is gravel in there, it will hold the moisture longer then if there wasn't a place for it to go. Make the bottom of the hole solid and water wont be drawn to it or have a place to stay.

I think part of the issue here is soil type, part is location, and part is post type...and by that I mean people might be confusing barn posts with fence posts.

As to soil type, it makes a difference if the soil is mostly clay, mostly loam, or mostly sand, as each holds and reacts to water differently, as well as holds onto posts differently to resist downward pressure from weight and upward pressure from wind. This affects the size of the footing under the posts (none, gravel, or a precast disk) and whether spikes or a crossbar is used to keep the post in a concrete collar.

Frost also has bearing on all of this, as here in New England it can get under concrete and push it out of the ground, particularly if it is only at the top of a post, and how deep the frost action goes. What works in GA or TX doesn't always work in VT or MT or wherever. I saw a stretch of I-80 in western PA where all the sloped leading edges of every stretch of guardrail were concreted in place according to Federal "best practice" for highways. And every single one had been pushed back out of the ground by frost, for miles and miles, all pointed so that oncoming cars would hit a chunk of concrete, not just the sloping end of the rail as intended.

And lastly, fencepost vs. building post. Growing up in MA, we'd never put a fencepost in concrete all the way to the bottom. It would guarantee that water running down the post, or wicking in from the wood above would never leave the post and you'd have a concrete cup full of mush, even with treated posts. The same post straight in the dirt or set on gravel and then with concrete to hold it upright would be fine, as there was somewhere for the water to go. But people don't usually put roofs over and regrade drainage around fence posts (well, they may heap them up some, but not like you would with a barn) and the loads up and down on a fence post are usually less. So if you have the same post in a barn, with a roof over it and the ground sloped away, you might be better off than out on a fence line. Or you might get a roof full of snow melting against the walls with the ground still frozen not allowing it to drain away and be right back where you started.

Maybe it's just me, but I don't think there are any easy absolutes here, and so people will still need to keep asking "sand or clay? any frost out your way? can you increase the slope away from the barn at all? are you going to have an overhang?" when answering questions about poles.

 

[riversedge]

I'm working through plans to erect a barn and there is something I haven't been able to "get a handle" on. I'm thinking of setting PT 6x6 posts on concrete piers as footings. How can I set the concrete piers or forms in place and be sure that the PT posts will all sit in perfect position, such that they will all be plum and aligned? I know how to "square up" a footing and align the holes for the piers, but it seems nearly impossible that you could fill tubes with wet concrete, insert post brackets, and have everything so precisely aligned that all of the columns would be perfectly plum when finished. If I set concrete piers like this for a large barn (say 28 x 40? with metal receptacles for the wood posts embedded in the concrete, IJust cannot image achieving the kind of precision needed to avoid having to tap the columns into plum.Just

Am I missing something here?

Thanks!

Just finished 13 piers using batter boards/string. Set string for the outside edge of my
piers. Marked and cut cardboard pier forms to length, cut forms about 1/4 inch short. Placed form on concrete footing. Filled form with about a foot of concrete. Leveled and adjusted position, filled to about half. Loosely backfilled to stabilze, topped off and screeded. Leaving the forms slightly short allowed just enough adjustment to plumb into alignment. I had similar idea and will be using a 6X6's for a base as I might need to move building in future. The piers are to provide better support by getting below my loose fill and frost line.

t. Placed PPlaced form