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