Posts in cement covered in tar?

[Daburner87]

Saw a guy setting a large timber in cement, probably 4ft deep and I noticed the bottom of the post was coated in something.  Is it common to coat the wood in tar before setting in cement to prevent rot or was it something other than tar?  Usually I see posts on top of cement piers with Simpson Strong-Tie hardware, but I've never seen this method before and think it must be incredibly strong considering the 6x6 timber is 4ft in ground.

[Don P]

Putting a post in the ground is one way of picking up some of the bracing. Surrounding the post increases the area in contact with the sides of the hole so increases that lateral bracing. A footing at the bottom and a collar or slab at the top are other ways of constraining the post. For the goop on the end, first I'd check the treatment and get something with UC4 (ground contact) on the tag There are all manner of concoctions and devices to prevent rot in a rot prone situation. The first question is, do you need to be in that situation? Can you brace the building with walls for instance. If there is another way to achieve the goal of support and bracing without putting wood in the ground, its worth looking at.

[fluidpowerpro]

I built a shed in 06 and my financial situation at the time was not good. I couldn't afford treated posts so I went cheap and sawed my own posts out of Red Oak. I too thought coating them in tar would help. I used black jack roofing tar and cement them in. They ended up lasting 10 years after which I replaced them with treated. My feeling is that the tar didn't help or maybe made them rot quicker by trapping moisture in. 

[kantuckid]

Plastic sleeves are common lately. 

[Tom King]

They're going to get wet inside.  I always thought anything that would help hold water inside would only make it worse, but never put two side by side to test.  I would guess it's just wishful thinking, but it's just a guess.

[Daburner87]

I built a shed in 06 and my financial situation at the time was not good. I couldn't afford treated posts so I went cheap and sawed my own posts out of Red Oak. I too thought coating them in tar would help. I used black jack roofing tar and cement them in. They ended up lasting 10 years after which I replaced them with treated. My feeling is that the tar didn't help or maybe made them rot quicker by trapping moisture in.

Out of curiosity did you happen to stain and seal the exposed red oak at any point in time?  I'm thinking of using red oak as well as I have an abundance of it, and I have a really good stain/sealer that I like.  I have no problem getting the post hardware to keep them up on top of the cement piers, but I'm curious of other methods.  Good to know it doesn't work. Wish there were more alternatives to the Simpson Strong Tie stuff.  

[Don P]

If it just need uplift protection a steel "knife plate" cast or bolted to the footing and inserted into the post and then cross drilled and pinned works. Slide some polycarbonate, a shingle, something to get the wood up and out of contact with the concrete. If I need to pick up "some" lateral I've cast an angle iron into the footing and run it up the post corner and lag it in. If you can get the lateral bracing from elsewhere it is better.

[Ianab]

Posts set in the ground will usually rot off close to ground level. Deep in the hole they may be wet, but there is little oxygen for the decay organisms to use. Hence "bog wood" that can survive being buried for thousands of years. 

Years back my Dad built a large pole shed at our farm. It was built pretty sold with ~14" treated pine poles with concrete footers and ring supports at ground level. Did well until a big windstorm ripped the iron and wooden stringers off the posts. Noting those were the weak point Dad bolted the replacement stringers to the posts, they wont move now. 

Even worse storm a couple of years later simply sheared the 12" poles off at ground level and whole sections of shed when bouncing off downwind. 

But the foundations never shifted. Wasn't an issue with uplift or lateral bracing, just the wind speed was more than the poles could handle.