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The mailbox is mounted on a 4x4 that was sunk into a concrete base about 18" below ground level. The 4x4 snapped off about 6" below ground. I really don't want to excavate the concrete and re-pour.

Is there a sleeve or joiner made that I could slide both sides of the snapped 4x4 into in order to secure each side with screws and join them (below ground) before re-mounting the mailbox? Where can I find something like this? The break on the post is jagged and I don't know that I can excavate the part of the post in the ground enough to square off the top so I could use a simple joiner with a plate in between the two post pieces. Any ideas?

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    Common in snow country to put the post back several feet and mount the mailbox on a beam set on top. Gets the post out of the road, and if you go to the high end of (but within) the allowable box height the plow wing can slide under it without damage. Leave the back of the beam long and either counterweight or tie it down with a cable. If you use only one bolt to mount the beam, it will swing away when hit, rather than try to stay put and be more likely to break.
    – Ecnerwal
    Jan 17 at 1:39
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    Worth checking if that type of mailbox mount is even still legal where you're at. In my area, they are transitioning everyone to a style that sits back several feet from the road,, and than has a gooseneck, swing-away piece that the mailbox sits on. If the plow or snow hits the mailbox, it simply swings out of the way and then returns to its normal position. See amazon.com/SwingAway-Mailbox-Support-Galvanized-Impacted/dp/… Jan 17 at 15:00
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    Depending on the jurisdiction, you might be able to get the plow company to pay for the repairs. In the US, damaging someone's mailbox is technically a federal crime, though it might be more trouble than it's worth to get compensation for it. Jan 17 at 16:40
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    Excellent point, @DarrelHoffman! Our state's DOT has an email address dedicated to reporting snow plow damaged mail boxes. Fortunately, we've never had to deal with it, but it seems that they're pretty responsive.
    – FreeMan
    Jan 17 at 17:16
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    I feel this whole Q&A is based on a false initial premise. Traditional construction wisdom is that you never put wood posts in concrete, because wood will eventually rot and need replacement, even if it didn't break before this, and wood has enough surface area that it can be adequately supported by bare dirt. Concrete only makes replacement difficult. For posts with large side forces like the ends of a high tension wire fence a "dead-man"(any rigid material) can be buried next to the post to increase dirt contact surface, but this is next to the post so the post can still be replaced.
    – Max Power
    Jan 19 at 22:26

11 Answers 11

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THIS ANSWER IS WRONG! I misread the question as the 4x4 having broken 6 inch ABOVE the ground...

With 6'' (15cm) above the ground remaining (assuming that those 6 inch are solid and you already trimmed off any splintered bits), you should have enough left to use angle joints*.

Cut off the bottom piece of wood in such a way that the most non-splintered wood remains (this can even be at an angle), then cut the new 4x4 accordingly (flat or in the mirrored angle as the bottom), then use two longer (or broader?) angle joints in the area where both pieces connect so that the wood is (almost completely or fully) surrounded by metal. Then drive in screws as you see appropriate. Ideally you want a really really long angle joint of 2x 6 inch, so you use all of the wood that's still in the ground for max stability

This solution would be by far the easiest, and with the right angle joints and enough screws also very stable.

*sorry for the German link, it's just to show you that somewhat right-sized angle joints exist [btw. I'm not even sure angle joints is the right word, but now you have a pic so you can maybe search with the right word]. The one linked is only 1.5 inches broad, so maybe too slim for a 4x4 (the broader the joint, the more stability), and with 7.8 inches on the shorter end, but a) I'm sure there are bigger ones b) with it being so slim you could use one for each corner instead of 2 angles c) even with just 2 of these it should be enough stability for a mailbox.

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    OP said > The 4x4 snapped off about 6" below ground.
    – Codex24
    Jan 18 at 18:12
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    @Codex24 oh. uhm. yeah that invalidates my entire answer lol. My head changed it to "above" somehow when i read it...
    – Hobbamok
    Jan 19 at 9:38
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Ground screw.

enter image description here

source

Screw this down through the old wood post. The depicted ground screw is 27 inches but I am sure you can find others if that is too long. The screw will be anchored in the old wood all the way down and through into the concrete. The top of the ground screw will hold your new post.

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    I can't imagine being able to run this massive thing into wood.
    – isherwood
    Jan 18 at 17:38
  • @isherwood - then drill a pilot hole you imagine will admit the ground screw. The idea is to take advantage of the wood and concrete already at the correct site.
    – Willk
    Jan 18 at 18:44
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    The threads on that are huge, and the shaft is tapered. Ain't gonna happen. All those upvotes are from people without much practical experience, I'd say.
    – isherwood
    Jan 18 at 19:26
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    The shaft of that screw has a 2.67 inch diameter. That means after drilling it into a 4x4 post (which is actually 3.5x3.5), there will be less than a half inch of wood around the shaft. It also means you're going to need a hell of a drill for the pilot hole. Jan 18 at 21:58
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    @CareyGregory I am counting on soggy wood underground.
    – Willk
    Jan 18 at 22:49
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If it broke off below grade, you can fill in the original hole and use a drive-in stake anchor for a new post in a new spot.

As long as you have the ability to move left or right a foot or so, this should be viable. Note that you’ll still need to call to have buried utilities marked before driving in the new anchor.

mailbox post anch

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  • I would think a strong enough blast of snow from a snowplow would uproot this.
    – rtaft
    Jan 18 at 15:23
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    @rtaft, the point of this is that it's capable of being staked down again without being permanently damaged, as well as being able to easily replace the 4x4 if it becomes damaged. Jan 18 at 18:55
  • I used one in a prior home, and it was surprisingly stable. Especially in winter, when the ground is frozen.
    – Tim B
    Jan 18 at 20:38
  • I've repaired a couple of fence posts using this method - but I have tried to dig out as much of the old wood in the concrete as possible first (in my experience, it'll be wet and pretty rotten if it's snapped above). Get it out by any means - drills, crowbar, swearing, whatever. Then put the stake in and concrete up to the top of the stake part (the bottom of the square bit). If you got plenty of the old wood out, then it'll hold pretty well. No concrete digging required, and only a bit to pour to fill the hole (I've used postcrete as its not really "structural" and super-easy to use). Jan 19 at 14:04
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This might be overkill, but it does solve the "no re-pour" requirement

  1. Get some concrete and a single post tie designed to be put into concrete (i.e. for decking). You can typically find these in the area with pressure treat 4x4s. Make sure you buy fasteners as well (deck screws and/or galvanized bolts)
  2. Pour concrete into the hole. Put your post-tie into your wet concrete and let it cure
  3. Cut your new post to size and mount to the post tie

Again, this is overkill, but it would afford you a (theoretically) easier to replace post the next time around.

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    This is how to do it right the first time around, and possibly the right way to fix it now, depending on how much effort you're willing to put in to make life easier for the next person that has to do this (which may or may not be OP)
    – Z4-tier
    Jan 17 at 21:05
  • If the post is broken 6" below ground level, there might not be enough depth to fit a concrete anchor into the hole. This image suggests they need about a foot: lawsons.co.uk/product/category/1157/… Jan 20 at 11:09
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I had the exact same problem. I got a 6 foot dig bar and just chopped the heck out of the 12 inches of wood remaining in the square hole and was able to remove all of the wood. I got a new 4x4, cut it to the proper length and rammed it into the existing concrete hole and then screwed the mailbox on to the top of the new post. I've done this with fence posts many times too.

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  • This would be a bad idea for anything that needs to be structurally sound, but for a mail box this would almost certainly be more than enough
    – Kevin
    Jan 19 at 0:17
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For what it's worth. You are only borrowing trouble if you don't remove the old post. The trick to removing a post is that you do not dig it out. You attach a jack to it and pull it out.

Your challenge is that your post is broken off. Drill a pilot hole and them use a 6" lag bolt to secure a piece of chain to your stump. Attach the chain to your jack and pull it like a tooth.

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Can you dry everything thoroughly and just glue the 4x4 back together? It's a mailbox, so it doesn't cary a large load. You'll need waterproof glue. Probably polyurethane. You'll need to clamp the pieces together while they dry.

Would this help: https://www.homedepot.com/p/Simpson-Strong-Tie-E-Z-Base-Black-Powder-Coated-Post-Base-for-4x4-Nominal-Lumber-FPBB44/100655350 I'm not sure how large the broken area is, or how much access you have below ground.

You can use the "wings" on that product to attach a 1x4 along the sides of the post, if it needs extra support.

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  • Interesting idea. How are you proposing one clamp this vertically? Also, since it's noted to be a very jagged break, getting a good, tight fit between the pieces of wood to allow the glue to actually hold and have any hope of a strong bond is going to be very difficult. At a minimum, epoxy should be used because it can fill the gaps where the wood doesn't meet tightly and still retain strength.
    – FreeMan
    Jan 17 at 13:06
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    Here's another option, but it may not be work since the break is sub-ground level: homedepot.com/p/Fence-Post-Repair-and-Mailbox-Post-Repair-PD10/… Jan 17 at 14:17
  • @FreeMan I bet if you were to just absolutely slather the thing in epoxy and then pound it in with a sledge hammer (maybe anchor it to hold things level while it dries, just like you'd do with fresh concrete), it would probably hold up pretty well. +1 for being the answer that burns the fewest calories (it's winter, I need my fat reserves).
    – Z4-tier
    Jan 17 at 21:09
  • This would only work if the break hasn't resulted in some of the 4x4 halves losing bits/splinters along the way. Ideally OP would cut down both halves to be flat and then glue them together, but they can't do that if they only have access to one half for modifications.
    – TylerH
    Jan 17 at 22:13
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It happened once, it will happen again.

I'd start by getting as much of the old post out as possible. Perhaps a hole saw on the end of a longer shank would chew out the center. Another option is a larger forstener bit to munch the remains of the post.

(Updated - not recommended) If you're competent with a chainsaw it may be possible to plunge-cut downward and eat out the post from the inside. This needs a long bar and a chain you're prepared to damage if it kisses the concrete. Plus kickback could be horrendous. (I'm no chainsaw user, check with someone qualified)

A shop-vac would help to pull out dislodged pieces and keep drilling.

A crowbar or pry bar would help push splinters off the walls and corners of the hole.

You might be tempted to try and burn the wood in the middle out - however that runs the risk of cracking the concrete, presuming you can ignite a fire with limited air supply. Plus it will be treated wood and that's both hard to light and releases nasty chemicals once it is burning.

When the hole is clear, use a spokeshave to subtly taper the new post for the depth of the hole, and then sharpen the bottom 2 inches/50mm to a 90 degree point. Drop some sand or gravel, or some wet concrete into the hole and fit the post. The gravel will form a "cup" to reduce rocking due to the slight taper. Concrete will do the same but will form a socket.
Next time the post needs replacing, simply bring up your old measurements and carve a new post with a taper and point. Then either just lift out the stub by hand, or screw an eyebolt into the stump and lever it up and out.

You may need to cut one or two thin wedges to hammer into the post hole beside the post, to take up any slop. Or you could use a sealant around the top to try and minimise rain/snow ingress.

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    FWIW, I've done my fair share of chain-sawing but I wouldn't dare to try such a plunge cut. Those are always really tricky to pull off even when you're trying them horizontally and not in a confined space. The chain going around the tip is going to try swinging your bar up (or sideways in this case) which is quite hard to resist with nothing to brace against, plus it has a really long lever arm. I'd say you're nearly guaranteed to slam the bar right into the concrete, breaking the chain in the process and throwing your saw back at you (the "top" side of the bar will hit concrete first).
    – TooTea
    Jan 18 at 8:40
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    I'm gonna give you a vote just for mentioning a spoke shave! TBH, that is not the most common tool in the garage...
    – FreeMan
    Jan 18 at 13:20
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    Do not do this with a chainsaw.
    – Sean
    Jan 19 at 20:06
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You can get a steel 'repair spur' that is designed to be driven into and around the broken post. They are shorter than normal steel post spikes

repair spur

Alternately, you could fit a bolt down anchor over the hole (possibly filling the rest of the hole with concrete first)

bolt down anchor

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Cut the top and bottom off of a 2-liter plastic bottle, forming a long cylinder. Slide this cylinder over the stump of the post. Apply wood glue to the surfaces of the post and then slide the remainder of post into the cylinder, matching the broken edges together. Then use a heat gun on the cylinder of plastic to shrink it tightly to the two halves of the post. -Note: I've never tried this, it's a suggestion I've seen on Youtube.

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    The OP said the break is blow ground, so there's no way to apply the bottle. Jan 18 at 18:59
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    Even if the break was above ground a shrunken 2-liter bottle is almost certainly not going to be strong enough to securely and safely hold a 4x4 post, and it definitely won't retain much strength over time when it's sitting out in the sun. Leave YouTube life hacks out of actual home repair
    – Kevin
    Jan 19 at 0:39
  • I disagree with both comments. Below ground, you would need to remove soil around the post to well below the break so you could blow a heat gun all around the sleeve to shrink it. Kevin's comment is obnoxious, and does not reflect ever having made a repair in this way. This type of repair is incredibly strong. Below ground, there is no sun. A 2-liter bottle would be too small. You would need a PETE bottle 5" diameter and long enough to extend a good 3-4" past the break top and bottom on wood unaffected by the break. This will only work for wood that has not rotted, which buried posts do.
    – fixer1234
    Jan 20 at 22:58
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Another option is a fence-post mender from Simpson.

I don't know if it will work in your case, but I've had success with using them on fence posts that have rotted out inside the concrete footer (their stated use case).

In theory, you could bolt two ties on the bottom of your new 4x4, then drive the menders between the snapped off remains and the existing concrete. Might work after a lot of effort with a pile-driver, or a large sledgehammer if you don't happen to own a pile-driver.

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