Joining multiple 4x4 pressure treated lumber together - Woodworking Talk - Woodworkers Forum
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post #1 of 32 Old 02-24-2019, 12:29 PM Thread Starter
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Red face Joining multiple 4x4 pressure treated lumber together

I am looking for some advice on how to join 5 4x4 pressure treated lumber pieces together. I am looking to create a new mailbox stand for our front yard and while I have a plan in mind I am having trouble figuring out the best way to attach the wood together. I am pretty new to wood working and have only completed a handful of simple projects and I could really use some expert advice as far as this mailbox construction is concerned. I got my inspiration for the project from this picture.


I know enough about wood working that I cannot simply glue the pieces together and hope that despite the weather that everything holds together. Any ideas, suggestions, even critiques on this project would be most helpful. I have attached a rather imperfect diagram of my design. Thank you so much for your help.
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post #2 of 32 Old 02-24-2019, 12:43 PM
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If the wood has been dried from the factory there isn't any reason you couldn't joint the wood straight and glue it together. Over time there may be considerable pull on the joints from wood movement though. It would be helpful if you would drill through the center of the boards and when you put it together put a couple threaded rods through the wood. Counter sink the ends to where a plug could be glued in the ends to hide the rod. I think the hard part will be lifting the post into the ground when you get it done.
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post #3 of 32 Old 02-24-2019, 12:47 PM Thread Starter
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How many thread rods would you recommend? One on top and one on bottom?
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post #4 of 32 Old 02-24-2019, 12:49 PM
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I like Steves suggestion of metal rods, plugs could be optional in this situation if the nuts are inserted, you may need to tighten the nuts if the posts shrink.
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post #5 of 32 Old 02-24-2019, 01:02 PM
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Originally Posted by EggNoggStick View Post
How many thread rods would you recommend? One on top and one on bottom?
One at the top and bottom should be sufficient. The one at the bottom should be above grade though.
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post #6 of 32 Old 02-24-2019, 02:04 PM
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I like Steve's use of threaded rods. I would add a touch of my own though. I built a huge sliding door from 3" stock for exterior use. I worried about expansion and contraction all year so I used threaded rods but on the outer edges I installed rocker arm springs you buy at the auto parts store. It allows it to expand in the wet south Texas winter and the springs will expand and keep the boards tight in the dry summer months down there. Torque them down pretty good. Worked good for me.

Word of caution though, you will say more than a few cuss words lining all that up while tightening it. Of course you are only doing 4 boards so that helps.
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post #7 of 32 Old 02-24-2019, 04:51 PM
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As soon as I read your post, I thought "threaded rod", too, but the others beat me to it. Here is one thought not yet mentioned:

In many places, it is good practice to separate the wood from the concrete. Where I live, if we were to put the outer 4x4s posts 12 inches directly into concrete, then the mailbox stand would break away in a few years at most. We use metal supports set in concrete, and attach the post to the metal supports with a slight gap or a non-wood spacer.

You can find the metal supports at your local big box store. The ones I use have a wavy metal plate for the concrete, and lots of bolt holes for the wood. I like the Simpson Strong Tie brand, which include the appropriate bolts with the product.
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post #8 of 32 Old 02-24-2019, 05:12 PM
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It's about the gaps ....

The thing I see is the moisture rain, etc will get down in between them in the gaps and eventually cause it to rot. I would coat the faces with asphalt roofing compound to close the gaps. I think standard threaded rod will rust from the acids in the PT will not last all that long. Ceramic coated construction lags would be better. They could be set in counterbores to make them less visible and if you are making an assembly of 4 posts, and come in from all sides. I would also use 4 X 6 posts for a wider front face. Stagger the heights for more visual interest as well. Coat the tops with roofing compound as well because the nature of the material is to crack from the top as it is a center section of the log. There are metal post caps that are decorative like this:
https://www.postcapdepot.com/postcap...RoCa8kQAvD_BwE

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #9 of 32 Old 02-24-2019, 05:38 PM
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Spax T-STAR WASHER HEAD POWERLAGS
I buy at Menards individually
I would use 5/16 x12
come from both sides into the middle
should come about halfway into the 4th 4x4(3 1/2+ 3 1/2+ 3 1/2 + 1 1/2)
use 4 on each side leave the head exposed, tighten as needed thru the years
built swing set with them 7-8 years ago and have not needed to tighten them yet(central Ohio)
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post #10 of 32 Old 02-24-2019, 07:46 PM
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Quote:
Originally Posted by EggNoggStick View Post
I am looking for some advice on how to join 5 4x4 pressure treated lumber pieces together. I am looking to create a new mailbox stand for our front yard and while I have a plan in mind I am having trouble figuring out the best way to attach the wood together. I am pretty new to wood working and have only completed a handful of simple projects and I could really use some expert advice as far as this mailbox construction is concerned. I got my inspiration for the project from this picture.


I know enough about wood working that I cannot simply glue the pieces together and hope that despite the weather that everything holds together. Any ideas, suggestions, even critiques on this project would be most helpful. I have attached a rather imperfect diagram of my design. Thank you so much for your help.
Hello EggNoggStick,

If your not wanting to get into more traditional woodworking joinery systems (simple or complex), and just need a super..."quick fix"...to putting in your Mail Box Post assembly that is fast, and strong enough for you design, then I would recommend a simple structural adhesive.

You can glue them together with a structural construction adhesive like PL Premium you can get at any "Big Box Store." This is more than strong enough to meet the load requirements, and is the same adhesives we use sometimes for "live load" applications in architecture...

I also would not recommend (at all) setting them in a concrete mortar of any kind. This just accelerates decay by trapping moisture within the interstitial regions of the wood, even in pressure treated wood...

Back filling with large elliptical stone set on edge and/or 3"-4" rock at the bottom of the post hole well packed in 9" lifts will create a well drained and tectonically stable footing for the post assembly. Filter cloth around the perimeter of the hole can help further by keeping out sediment. Take the stone all the way up at least 2/3 the barring depth and then back fill further with a draining finish gravel that is appealing to you aesthetically...

If you would like to explore some simple joinery systems to expand your woodworking skill and not require more than basic hand and/or shop tools, I can expand on that further if you wish...

Good Luck...

j
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post #11 of 32 Old 02-24-2019, 08:06 PM
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I've built wood carving work benches out of 4x4 and used threaded rods and lag bolts to join the pieces.
Don't put the ratchet wrench and socket away. Every month or two, most nuts need 1/4 turn to stop the wobbles.
So,
I don't think threaded rod is the way to go.
Construction adhesive will also fill the voids between the pieces.


Don't forget the cut the tops at 45 degrees or something for drainage.

Water proof the hello out of that endgrain.
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post #12 of 32 Old 02-24-2019, 08:40 PM
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Quote:
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...Don't forget the cut the tops at 45 degrees or something for drainage.

Water proof the hello out of that end-grain.
Yikes...Dang it...!!!

I forgot that...!!!

We very often put a small spacer block on top (end grain) of such exposed post assemblies and then not only traditionally finish the wood with oil and beeswax, but also cap it with a stone, copper or related flashing material...Plus, this adds a quick and easy decorative finished touch to the project...!!!...besides taking care of the second spot they usually start to decay...

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post #13 of 32 Old 02-24-2019, 09:09 PM
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I found a picture of one of those doors. This wasn't one of mine but I built the first two just like it. This one came on phase 2 with another carpenter who has now passed away. Good guy too. It has an active egress door in the middle when it's closed. I never figured out why the architect wanted it that way when you could walk around it. It's held together with the threaded rod and rocker arm springs to adjust with the weather.
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post #14 of 32 Old 02-24-2019, 09:34 PM
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Quote:
Originally Posted by mreynolds7714 View Post
I found a picture of one of those doors. This wasn't one of mine but I built the first two just like it. This one came on phase 2 with another carpenter who has now passed away. Good guy too. It has an active egress door in the middle when it's closed. I never figured out why the architect wanted it that way when you could walk around it. It's held together with the threaded rod and rocker arm springs to adjust with the weather.
"Threaded rod" assemblies of may type have grown popular in a number of..."non-exposed"...applications over the last few decades. I have even seen it in some of the "modernized" approaches to log home construction. In all applications that seem to be even relativity functional over time, they are:

1. Not exposed to the elements of any kind, and not in PT wood because of the corrosion issues thus far mentioned typical with many PT chemicals as well as just normal wet weather exposure and the trapping of water deep inside the wood core (aka interstitial zones)

2. There typically is spec'd by our PE to always have a "tension" system (aka springs etc) as part of the assembly in most (not all) applications...

Those look like some nice hanging doors in the modern motif that is growing in popularity with clients! Good Job!!!
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post #15 of 32 Old 02-24-2019, 09:52 PM
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Quote:
Originally Posted by Jay C. White Cloud View Post
"Threaded rod" assemblies of may type have grown popular in a number of..."non-exposed"...applications over the last few decades. I have even seen it in some of the "modernized" approaches to log home construction. In all applications that seem to be even relativity functional over time, they are:

1. Not exposed to the elements of any kind, and not in PT wood because of the corrosion issues thus far mentioned typical with many PT chemicals as well as just normal wet weather exposure and the trapping of water deep inside the wood core (aka interstitial zones)

2. There typically is spec'd by our PE to always have a "tension" system (aka springs etc) as part of the assembly in most (not all) applications...

Those look like some nice hanging doors in the modern motif that is growing in popularity with clients! Good Job!!!

Thanks. These doors are covered fairly good but blowing rain does get to them. To keep them from warping as much we used quarter sawn yellow pine. Untreated. In fact all the wood is quarter sawn pine as per specs. They never could get a decent stain that would last in the hot South Texas sun. I am not a paint guy so I was at a loss. Other than that it was one of my favorite jobs.
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post #16 of 32 Old 02-24-2019, 10:21 PM
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I like the threaded rod solution also, but I'll throw out a second method that I used back in 1989 that should require less drilling precision. I was building a 6 foot tall shadow box privacy fence around our yard to protect the inground pool we had just installed. The gate to the back yard was to be 4 foot wide and 6 foot tall and be quite heavy. I doubled the 4x4 gate posts and the queen post by using counter sunk stainless steel lag bolts and Gorilla Glue to join the two 4x4 pieces together. All three assemblies are still solid today. The assembly could be added to by simply doing the join again and again until the desired stack up was reached. This method only requires one set of plugs to cover the last lag bolts. I did four bolts per join as the posts were 10 feet long (four feet in the ground), but I tend to over build stuff.
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post #17 of 32 Old 02-24-2019, 10:49 PM
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Quote:
Originally Posted by mreynolds7714 View Post
...To keep them from warping as much we used quarter sawn yellow pine...
Simply brilliant...!!!...Good JOB!!!

I wish more folks (especially professionals) took the time to learn wood and grain patterns as it applies to the craft.

I'm virtually only a traditionalist in my work, so the coloring and finishes I would have spec'd for a project like that would have you using traditional oils, waxes and plant resins and probably blending your own pigments...LMAO...!!!

Would love to collaborate sometime if you still in "the game?" I'm suppose to be in Katy Texas in the next six months finishing a project. Where are you in relationship to there?
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post #18 of 32 Old 02-24-2019, 11:40 PM
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Originally Posted by EggNoggStick View Post
How many thread rods would you recommend? One on top and one on bottom?
If you go with the rods make sure they are hot dipped galvanized along with the nuts and washers.

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post #19 of 32 Old 02-25-2019, 06:59 AM
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Originally Posted by Tool Agnostic View Post
As soon as I read your post, I thought "threaded rod", too, but the others beat me to it. Here is one thought not yet mentioned:

In many places, it is good practice to separate the wood from the concrete. Where I live, if we were to put the outer 4x4s posts 12 inches directly into concrete, then the mailbox stand would break away in a few years at most. We use metal supports set in concrete, and attach the post to the metal supports with a slight gap or a non-wood spacer.

You can find the metal supports at your local big box store. The ones I use have a wavy metal plate for the concrete, and lots of bolt holes for the wood. I like the Simpson Strong Tie brand, which include the appropriate bolts with the product.

That is interesting. Anywhere I have ever lived it is normal practice to place the pressure treated 4x4 post directly in concrete when putting up a fence. They last many, many a year doing this.


I wonder just why the soil( or whatever?) is different in you area.


George
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post #20 of 32 Old 02-25-2019, 08:09 AM
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That is interesting. Anywhere I have ever lived it is normal practice to place the pressure treated 4x4 post directly in concrete when putting up a fence. They last many, many a year doing this.


I wonder just why the soil( or whatever?) is different in you area.


George
I agree. Sometimes though unscrupulous companies will hose the treated wood down with the chemical to give it the green color and sell it as pressure treated. I've always put treated posts in concrete and the only ones that failed were the ones that weren't pressure treated. I've got a round post on my place you wouldn't know anything was wrong with it unless you handled it. It's completely hollow in the center all the way to the top. The post next to it that has been there since the 1980's is still good as new.

There has also been concerns about threaded rods corroding. The treaded rods are coated with something, I think zinc and I've never seen one of them corrode in pressure treated wood.
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