Help with putting post in ground with cement

paulri

paulri

Joined
Aug 14, 2015
Messages
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Location
CA, USA
I need to put a 4x4 holding up a mailbox, into the ground. I'm going to use quikrete for this.

Now the standard is to make the hole 1/3 as deep as the height of the post above the ground. I can't do this, because of regulations about how high the USPS wants the mailbox. Given the 4x4 that I have, leaving the minimum height (41 inches) above the ground, leaves me only about 8 inches to put in the ground.

So my question is, should I make the hole for the post, very wide, or just make it narrow and deep? Remember, there will only be about 8" of post in the ground.
 
You will need more than 8" of depth to support that properly.

Listen, go buy a new 4X4

Now the hole should be wide at the bottom and narrow at the top. Think like a pyramid or a sack of marbles. Mass down low. Heavy top in the concrete will not be as stable, but only a mailbox so straight hole OK if plenty of concrete.
 
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You are trying to cobble a footer of some sort I guess. A fart will tip that over. Getting a longer 4x4 would be a better choice. They come in 8 feet and would accommodate your height and depth requirement. 2 - 60 lb bags (pref 80) will do.
 
Can you get a longer 4x4? Or get a few long (12") Lag Bolts screwed into the bottom sticking out 6-8" or so, so that they are in the cement. We have a similar situation-can not dig deeper due to concrete in the hole already and can not bust it up. We will go with a wider hole and drive some nails into the base sticking out like a porcupine to give the cement more bite.
 
'round here you'd want to dig at least 4' down. Need to get below frost line. I see you are in California, but it's a mighty big state, so I don't want to assume here.

8" won't hold much. Snow plow is going to take that out on the first storm. Might as well put the 4x4 into a bucket of sand--don't laugh, at my old house I did that, and it lasted years. Until a neighbor hit it... with his snow plow...
 
It would be easiest for me to use the 4x4 I have, because the mailbox is attached to a 1" board that itself is connected to the 4x4.

This 4x4 without cement, has held up for 5-10 years, so my pouring in at least some cement, should let it hold up even longer. At least, that's what I'm thinking.

But yeah, I see that a new, longer 4x4 would hold up better.
 
paulri said:
It would be easiest for me to use the 4x4 I have, because the mailbox is attached to a 1" board that itself is connected to the 4x4.

This 4x4 without cement, has held up for 5-10 years, so my pouring in at least some cement, should let it hold up even longer. At least, that's what I'm thinking.

But yeah, I see that a new, longer 4x4 would hold up better.
Click to expand...
Good luck.

Scott
 
paulri said:
It would be easiest for me to use the 4x4 I have, because the mailbox is attached to a 1" board that itself is connected to the 4x4.

This 4x4 without cement, has held up for 5-10 years, so my pouring in at least some cement, should let it hold up even longer. At least, that's what I'm thinking.

But yeah, I see that a new, longer 4x4 would hold up better.
Click to expand...

If you are dead set against using a new longer 4 x 4 post, you can make the current one work if you dig the hole 18"-24" deep and use an 8" o.d. cardboard cylindrical concrete form to establish a deep concrete base to embed the bottom 8" of the post. When fully set, the additional depth and weight of the concrete base will anchor the post securely. Cardboard tube forms are available at Home Depot and Lowe's near the bags of concrete.
1732324856558.webp
 
HD also sells one with a 12" diameter. Would that be better, or overkill?

Again, this is just to keep a post upright, that has been upright standing upright in dirt for 5-10 years.

Nukeman7 said:
If you are dead set against using a new longer 4 x 4 post, you can make the current one work if you dig the hole 18"-24" deep and use an 8" o.d. cardboard cylindrical concrete form to establish a deep concrete base to embed the bottom 8" of the post. When fully set, the additional depth and weight of the concrete base will anchor the post securely. Cardboard tube forms are available at Home Depot and Lowe's near the bags of concrete.
Click to expand...
 
paulri said:
HD also sells one with a 12" diameter. Would that be better, or overkill?

Again, this is just to keep a post upright, that has been upright standing upright in dirt for 5-10 years.
Click to expand...
8" o.d. is plenty of you dig the hole down to ~24". The 12" o.d. would be unsightly and overkill. 12" o.d. would also require a lot more concrete. The amount of concrete needed per foot of depth is printed on the side of the form tube as a general guide.
 
If you have a quality post hold digger you should be able to dig a 24" to 30" deep hole without much difficulty.

Helpful hint: If the soil is hard dig as deep as you can. Say you can only go 8 or 10 inches. Stop. File the hole with water and let it soak in for a few hours. Dig another 10 inches until it's making you work too hard. Fill the hole with water. Repeat.

As long as you're actually digging into dirt (not rock) you should be able to dig a 30" deep hole without too much trouble. Also too, I think using the type Quikrete that you pre-mix with water in a wheelbarrow is better than dumping the dry mix stuff into the hole and then backfilling with water.

Importantly, do no fill the bottom of the hole with 4 or 5 inches of concrete and then set the post. The water that leaks past the post/concrete on the surface will never drain. I always put 3 or 4 inches of pea gravel in the bottom of the hole, then put the post in, then put the concrete in.

FWIW,

Scott

Edit: Whether you use a pre-treated or construction heart redwood, treat the post that's going to below the surface of the ground with copper-green.
 
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Nukeman7 said:
If you decide on a new 4x4 post, be sure it is pressure treated for GROUND CONTACT per the label. Otherwise, it will rot away in 3-4 years.
Click to expand...
Yes I'll definitely get pressure treated. I've started using that when I repair fence posts.
 
DO NOT FORGET to call the underground utility locator service and have it marked.. I have heard they charge a lot to splice a fiber line. '

Put the box post in a bucket with sand until you get it marked.

And a 4X4 will not withstand a snow plow,

Rod
 
paulri said:
I need to put a 4x4 holding up a mailbox, into the ground. I'm going to use quikrete for this.

Now the standard is to make the hole 1/3 as deep as the height of the post above the ground. I can't do this, because of regulations about how high the USPS wants the mailbox. Given the 4x4 that I have, leaving the minimum height (41 inches) above the ground, leaves me only about 8 inches to put in the ground.

So my question is, should I make the hole for the post, very wide, or just make it narrow and deep? Remember, there will only be about 8" of post in the ground.
Click to expand...
One more thing to check - "regulations" you mean HOA? Is the exposed concrete tube OK?
 
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