[douglas sloan]

My contractor dug 3 feet holes and used a bag and a half of cement, but that still doesn't fill the hole. He said we should just fill the rest of each hole with dirt. It is treated lumber posts but won't it rot if it is not cement all the way to the top of base. Also if I buy more cement for 55 posts it could cost me another 300 dollars. What should I do.

 

[DangerMouse]

don't feel bad, i thought the same thing.
i was told by the building inspector here to seal the ends of the posts and fill the hole with dirt, he said it'll rot FASTER if covered with cement as you describe.
but the inspector that told me that could be wrong....

DM

 

[MrBill]

I have read multiple articles that claim wood (PT & Cedar) will rot faster in concrete. One reason is due the lime in the concrete. Also water can seep in between the post and concrete.

 

[Daniel Holzman]

I don't believe there is any credible evidence that concrete itself causes rotten posts. Concrete is essentially an inert material, it will leach very small amounts of lime over time, but many soils contain lime naturally. The problem is that a post fully surrounded by concrete has nowhere to drain water, so the small gap between the concrete and the post tends to collect water, which in turn encourages rot.

The normal technique to minimize this possibility is to place the post on 3-6 inches of crushed stone. If you want even better drainage, you can place six inches or so of crushed stone in the hole alongside the post, then place concrete above that. The only real purpose of the concrete is to stiffen the post against lateral movement, you can actually achieve almost as good a result by using crushed stone surrounding the post, and compacting the stone in not more than 6 inch lifts. The stone will then drain properly, and will be nearly as stiff as the concrete, probably plenty stiff enough to minimize movement of the post. Saves the cost of concrete also.

We did all of our fence posts in crushed stone and sand, haven't had any rot or problems in 15 years. Posts are 4x4 cedar, by the way.

 

[Scuba_Dave]

I very rarely bury any posts anymore
But at my last house I did bury 4x4 posts for a lattice privacy fence
I didn't use any concrete, just rock that I pounded in with a sledge
The area did have fairly sandy soil & drained very well
I took it aprt 7 years later when we moved - no rot

Is this for a deck?
I wouldn't be too worried about it either way
I think I'd just fill with soil

I'm not sure if caulking between the post & concrete would prevent water seepage to any degree?

 

[DangerMouse]

maybe rubberband a plastic garbage bag to it before you 'crete around it? heh heh

DM

 

[biggles]

get yourself a 5 gallon bucket of roofing tar and dip the posts in it 3' let them dry up in the sun and ..............:thumbsupost away.do the concrete to secure them,then fill the rest in with all that FREE dirt

 

[Bigfoot]

I've painted (brushed on) Bitumen (roofing) products before to the parts of posts likely to be in constant contact with moisture. Also non treated beams laying on (or in sockets) on concrete or bricks. Seems to be decent moisture barrier that lasts. I've also used tin, plastic and tar paper flashings over the bitumen painted part of the post, in places that were likely to rot (heavy compost soil contact). A thick (construction grade) plastic molded s bit with a heat gun, works well as a moisture barrier.
If the posts have a chance to dry out periodically, they last a lot longer, constant contact with moisture (soil) accelerates rot. And is likely the first place rot or insects will attack a post with faulty or inferior impregnation.
You never really know the quality and thoroughness of the impregnation process until a decade has passed. Plain for the worst and hope for the best is my moto.

 

[Kap]

I've painted (brushed on) Bitumen (roofing) products before to the parts of posts likely to be in constant contact with moisture.

that's what I do for the part of post that will be below the surface. I also put 4-6 inches of gravel in the hole first for drainage under the post. And slope the top of the concrete so water will run away from the post.

 

[DecksEtc]

If you put the concrete all the way up to the ground level, frost will heave the post within 1-2 years (I am assuming you live in an area where there is frost, BTW)