Tips on vertical posts?

[DEWFPO]

I 've seen folks widen the bottom of the hole with a manual post hole digger and then cement the bottom of the post in so it won't frost heave.

DEWFPO

 

[EddieWalker]

Ray,

I won't argue about your local conditions, but do find it interesting that leaving a space for water to collect on top of the cement is something people do on purpose. What happens during the rest of the year when it's not freezing out? I would think that water will settle there and start the process of rotting the post.

If the cement was all the way from the bottom of the post to the top, how would that cause the post to heave out of the groud compared to less cement that only went up to 6 inches below grade? I would think that more cement would keep the post in the ground better then less cement.

Eddie

 

[radman1]

Ray,

I won't argue about your local conditions, but do find it interesting that leaving a space for water to collect on top of the cement is something people do on purpose. What happens during the rest of the year when it's not freezing out? I would think that water will settle there and start the process of rotting the post.

If the cement was all the way from the bottom of the post to the top, how would that cause the post to heave out of the groud compared to less cement that only went up to 6 inches below grade? I would think that more cement would keep the post in the ground better then less cement.

Eddie

Eddie

I agree with your logic. I live where it can be -20F to over 100F. I have never seen it done as Ray has described. I could see if one left the cement down from the top, it would be give a better appearance to the fence without any exposed cement.

I rarely use cement around a wood post unless the post is under a shelter and protected from rain/water. Cement is great at holding a post, but the post won't last as long. Not saying the post won't last for many years but it would have lasted much longer without the cement. For lots of posts, cement is also relatively expensive compared to the free dirt from the hole.

My sister's neighbor just replaced a section of their wood fence. 4x4 pressure treated posts cemented in the ground. 15 year old fence, posts rotted off at the top of the cement. Probably a matter of time before the rest starts to fall over in the next big wind.

 

[ray66v]

Ray,

I won't argue about your local conditions, but do find it interesting that leaving a space for water to collect on top of the cement is something people do on purpose. What happens during the rest of the year when it's not freezing out? I would think that water will settle there and start the process of rotting the post.

If the cement was all the way from the bottom of the post to the top, how would that cause the post to heave out of the groud compared to less cement that only went up to 6 inches below grade? I would think that more cement would keep the post in the ground better then less cement.

Eddie

Here, the best way is to leave the cement about 6" from the top, and finish it with dirt. This Dirt "cap" freezes first, and helps hold the post down.

It's actually the same concept as you suggest. The dirt on top, will direct most water away. Then, as I said the dirt on top freezes first, forming a barrier above the post. This helps to hold the post in the ground.

Also, the shape that ends up at the top, when you cement all the way up, gives a slightly larger top that is perfect for the frost to use to pop the post out.

Frost heave is not affected by weight, it lifts entire driveways with much more concrete then this.

This is a tried and true method. The only people that don't use it, are the ones who have not figured it out yet.

If I went around and took a few dozen photos of frost heaved, cemented to the top posts for you, perhaps that would convince you?

And I again, I agree, you should not cement wood posts, unless it is necessary, then only on ends, and at gates.

 

[radman1]

It's actually the same concept as you suggest. The dirt on top, will direct most water away. Then, as I said the dirt on top freezes first, forming a barrier above the post. This helps to hold the post in the ground.

Also, the shape that ends up at the top, when you cement all the way up, gives a slightly larger top that is perfect for the frost to use to pop the post out.

Frost heave is not affected by weight, it lifts entire driveways with much more concrete then this.

This is a tried and true method. The only people that don't use it, are the ones who have not figured it out yet.

If I went around and took a few dozen photos of frost heaved, cemented to the top posts for you, perhaps that would convince you?

And I again, I agree, you should not cement wood posts, unless it is necessary, then only on ends, and at gates.

Still not quite buying all of it. Correct me if I am wrong. Frost heave is caused by freezing water in the ground. (Ice expands as it freezes.) Agreed? This is why footings are placed below the frost line so that the expanding/frozen ground which causes heaving is above the bottom of the footing. Agreed? I would guess the posts that you see heaving are due to the cement being above frost line not because they used cement to the top of the post. You state that frost heave is not affected by weight. Which is true. Why then would dirt on top of the cement stop the heaving? A relatively thin layer of frozen dirt will not stop additional heaving as the ground below becomes frozen. If that was true, then wouldn't any frozen layer of ground over anything below it stop the ground from heaving.

I will agree with you, if the top of the hole is conical (top wider than the bottom), the problem of heaving is greater.

Most of the time, when I see cement used on posts is for a few reasons. One, the cement creates a larger surface area and thus makes the post less prone to leaning, for example a corner post like you stated. Second, some people dont want to put the post deep enough in the ground to anchor it solidly. I see lots of 6' high wooden yard fences put in with 8' posts. The builder doesn't want the expense of a 9-10' post to put in the ground. A third reason, is cement, if premixed, goes in the hole easy, requires less physical work than tamping.

 

[EddieWalker]

One more reason for concrete is in soft soils. Here, we have areas of sugar sand. It's fine for building on top of, but terrible for fences when the wind blows.

Eddie

 

[ray66v]

Still not quite buying all of it. Correct me if I am wrong. Frost heave is caused by freezing water in the ground. (Ice expands as it freezes.) Agreed? This is why footings are placed below the frost line so that the expanding/frozen ground which causes heaving is above the bottom of the footing. Agreed? I would guess the posts that you see heaving are due to the cement being above frost line not because they used cement to the top of the post. You state that frost heave is not affected by weight. Which is true. Why then would dirt on top of the cement stop the heaving? A relatively thin layer of frozen dirt will not stop additional heaving as the ground below becomes frozen. If that was true, then wouldn't any frozen layer of ground over anything below it stop the ground from heaving.

I will agree with you, if the top of the hole is conical (top wider than the bottom), the problem of heaving is greater.

Most of the time, when I see cement used on posts is for a few reasons. One, the cement creates a larger surface area and thus makes the post less prone to leaning, for example a corner post like you stated. Second, some people dont want to put the post deep enough in the ground to anchor it solidly. I see lots of 6' high wooden yard fences put in with 8' posts. The builder doesn't want the expense of a 9-10' post to put in the ground. A third reason, is cement, if premixed, goes in the hole easy, requires less physical work than tamping.

Ok, last try,

The ground freezes from the top down. Yes, the relatively thin layer of dirt on top does provide a barrier to help stop the heave. Certainly this barrier is more protection than having nothing provides.

The fact that the concrete is wider when run up too the top, as it always is, from simply digging or boring a hole, as loose topsoil, cave ins, and wobble, even if slightly, sets up the perfect conditions for the frost too tighten around the post, and squeeze it out of the ground.

Yes, if a post was concreted all the way down below the frost line, (about 4' here), and the top was not wider than the bottom, it would not heave, even with the concrete all the way too the top. However, short of using Sono tubes as forms on posts, (not practical), it is certainly much easier to stop 6" from the top and finish with dirt. And, as a bonus, you won't have to go down so deep, 32-36", for common posts, works just fine here.

As I said, this is proven science here. I have sent a lot of time fixing heaved posts, installed by others. None of which were a problem afterwords. Your welcome however, from here on out, to encourage those who supply me with work, by suggesting your method.

 

[mouse]

interesting.

another observation is that if your post has any sap wood on it it will lossen over time as the sap wood rots. if its in dirt then you can just tighten the thing up with a crowbar, if its set with concrete then how do you tighten the post...?