Cementing post footers?

gio17vaniOctober 15, 2006

I am building a hot tub deck and am using Treated 4x4 posts and cement footers sunk 43". My question comes from hearing 2 ways to secure the posts the first being to set the post in, plumb, and then add the cement letting it cure with post in it then backfilling. The second would be to pour the cement and allow it to cure before adding the posts and then backfilling. Then there seems to be more dispute on whether the posts will rot if surrounded by the backfilled dirt and that sand or gravel should be used. My soil is crappy with a heavy clay content so I do fear possible drainage issues.

My original thinking was to cement the posts into the footer after making sure they were plump and secure and backfill with some fine particled playsand I had left over from an aquiarium along with soil and clay being sure to pack it every foot or so.

I will be using fast setting concrete as well since here in michigan the weather looks like it will only stay in the mid 40's and 50's for a few days with today being the only day it won't rain. ( I will be covering holes with a tarp to avoid any excess moisture since there is enough in the ground)

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Make sure the post is rate for ground contact. Most of the PT is not.
You could make the whole problem moot by bringing the concrete to grade and using a post anchor to keep the wood from resting directly on (or in) the ground or the concrete.

    Bookmark   October 15, 2006 at 1:42PM
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John agrees with the Brick,land the posts on top of the concrete.

    Bookmark   October 15, 2006 at 2:36PM
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Right now I have 50lbs of cement in each hole so they are only about half full. I like the idea of bringing it above ground and using a j-bolt? about 3/4" out before it sets so I can then use the post anchor to sit the posts on. The only problem I have is this weather since it is either below 50, raining, or both for the next week and I fear that I wont see any more decent weather to get it done.

    Bookmark   October 15, 2006 at 8:19PM
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I poured my own footers by making a 12" square frame from 2X4s, so the footer rises 3 1/2" above grade. Dropped some 3/8" rebar in the concrete (it's cheap). Put in a J-bolt, bought post anchors for 4X4s. I've put alot of fence posts in concrete in my day. My preferred method is to put about an inch of gravel at the bottom of the hole, drop the post in, then fill with concrete. The idea is any water that seeps down will drain through the gravel, instead of hitting a roadblock.

    Bookmark   October 15, 2006 at 8:35PM
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No matter what you do, the bottom of the post must rest on a concrete pad a leat 6 inches thick. It cannot rest on soil. You need the concrete to distribute the load of the post across a wider area thereby preventing the post from being pushed deeper into the ground. This concrete must be below the frostline. This concrete pad or column does not need to be carried all of the way to the surface if the post is pressure treated lumber rated for ground contact! Here is what I do. I dig a hole about a foot deeper than the frostline about 16" to 18" in diameter and then pour in 2 60 pound bags worth of concrete (a fairly dry mix) into the hole. Tamp and let cure for a day. Next day I position the post on top of the hardened concrete and then plumb the post. I then pour in about 8 more 60 pound bags of concete around the post. I use a shovel to carefully drop the concrete around the post for the first 4 bags worth so as to not knock the post out of plump. Using the end of a 2x4, tamp the concrete after every few shovels full so there are no voids in the concrete. A concrete mixer is a must for this job. I have NEVER had a problem with rot using this method nor do I know of anybody else that has had a problem however you MUST use pressure treated posts rated for ground contact. If the end of the post you are putting in the hole has been cut AFTER it was pressure treated then you must soak this freshly cut end in a bucket of copper-based wood preserative for a hour before putting the post in the hole. This copper wood preservative comes in metal cans and is availabe at Lowes. The reason you must do this is because the chemicals used to pressure treat lumber only go into the wood about an inch and if you cut an inch off you have just created a post that will be susceptable to rot.

    Bookmark   October 16, 2006 at 5:19PM
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The posts should preferably be rated ground imbedment, which is the next higher treatment than ground contact.

Either a 31 for the new treatment, or 60 older type.

As others have stated, it is difficult to get the higher rated treatment.

I had to get my building supplier to special order it.

Took a little more time, not much more $$$, and I believe worth it.

I have read that the Jasco Termin8 has a strong odor if used above ground.

I don't think Copper Brown does.

I believe Joe Wood adds a copper collar to his posts, and also be sure to slope the concrete away from the post.

You can also add gypsum to loosen up and improve the drainage of the soil.

Good luck.


    Bookmark   October 16, 2006 at 8:25PM
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I learned that little copper trick from the Joe Mon,,the only time I put posts in the ground is with arbors then its .40 (.60 would be better but o well) usually 6x6s with copper flat stock installed with copper nails right at the top of the pour,half in half out. The more the copper leaches the more protection is given. Then I wrap the posts with what ever the contract calls for. Little trick>>> Most of the time we dont wrap the posts until the last soooooo protect the acq posts from the sun with felt paper until its time to wrap them

    Bookmark   October 16, 2006 at 9:36PM
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With regard to the post resting on concrete, what about using a preformed pier at the bottom of the hole? The post rests on the pier and then pour concrete around the post(?)

I like the idea of anchors so the post could be replaced if ever damaged. The trouble is you lose the stability at the base of the post. Just a thought.

    Bookmark   October 17, 2006 at 7:20PM
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Yea, looking at how a posts rests on a post anchor and is attached by nails, it would appear to be a weak link. But I guess if the posts are plumb and even better if the deck is attached to a building, its' forces are straight down. I estimate my 30X30 deck weighing about 3000#. That's alot of weight that wants to go down, not sideways.

    Bookmark   October 17, 2006 at 8:33PM
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Yes, all of the force will be downward for a typical deck. I'm planning a deck with screened porch and thinking also about wind forces so the lateral stability is important for me. I live in SE U.S. and we get some nasty storms blowing through. The screened porch will be extention of the house and will have a shed roof. That makes it essentially a big air foil. I have to consider upward and sideways forces too. I think anchors are out of the question in my case. Good advice above about additional treating of the post prior to set it. Thanks.

    Bookmark   October 18, 2006 at 1:27PM
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Gio, a couple of things, I'm in WI so we have about the same weather, if your in the 50's during the day, this is great weather to pour concrete,,,, a little rain even better. If it happens to freeze at night cover the posts up with a blanket or plastic or something but only if it freezes. Don't get me wrong your concrete will take more time to reach it's strength when it's 50 vs. 70 but it will be fine if you build your deck a week later on these posts. The others are correct but lateral bracing on this is very critical with the hot tub going on top... just curious how high off the ground will this deck be???
Thanks Dave

    Bookmark   October 19, 2006 at 1:59PM
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"Yes, all of the force will be downward for a typical deck. "

As long as everything stays square and perfect. It never does for very long.
The racking force is still typically well within the holding strength of the nails attaching the post to the base.
Through bolts are even better though. For taller posts (above about 8 feet) I really prefer to use fabricated steel anchors with expansion bolts to the concrete and through bolts to the posts (6x6 and up). I have a welding ship make them for about $15 each from #10 steel.

    Bookmark   October 19, 2006 at 7:18PM
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I have a question about posts. It seems like there neeeds to be a lot of protection for the wood and preperation for the wood using pressure treated pine lumber. So my question to you guys is would there be a market for an alternative to pressure treated pine posts using posts made out of tropical hardwood? There are many species of wood that are extremely long lasting with ground contact and really do not have much of a market as lumber, so they are cheap. We have the worst possible climate for wood in the world, high humidity, constant hot temperatures, all kinds of fungus, and a wide variety of termites. Ipe is an example of this kind of wood, but there are species are more resistant, especially in ground contact situations. One of these, angelim vermelho (Dinizia excelsa)I have personally used in ground contact and I think that if I live another 50 years it will still be in great shape. They use this wood in Holland extensively to line the dikes with. It does have one drawback though, when green it has a smell very simlar to dirty socks. This would probably make it difficult to sell in the US market. I made a fence recently using this as the posts, 4 x 4s, and it is a question of a few months until there is no smell at all. But, there are many others without this problem. It would seem that wood with no chemicals at all may have some market, although limited. I realize that most homeowners do not probably care what the wood is under their decks, but I am always curious to see if there may be markets for wood that more fully utilizes the native forest species we have here. Maybe in large urban areas with high environmental standards, like Southern California it would be possible to create a market. It would not be something people could just pop over to Home Depot and buy though.


    Bookmark   October 22, 2006 at 8:28AM
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Hey Don,the Port Orford Cedar has a really high smell and is used up in Oregon. I think the only hold up would be marketing, the box stores have a strangle hold on what gets sold around here.
I would use the angelim in a heart beat if I could get it, that would be a great sales item. Farily often I get a Customer asking how long the .40 acq is going to last up against ipe thats good forever far as our lifetime goes.I have no anwser to that because no one knows.

One way to fasten post base to the pier is with the Hilti two part system and threaded rod, this stuff sets up real fast and a person would have to use a jack hammer to get them out. John

    Bookmark   October 22, 2006 at 9:23AM
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After 15 years, I needed to replace all eight of my stair landing posts. Rated for ground contact, but that wasn't the problem. They rotted from the end grain on the top as they hadn't been properly flashed. The replacements all have 16oz copper sheet caps secured with copper slaters nails. A lot of fun, jack the rotted post slightly to unload it, take it down, put the new one up and pour a new/better foundation for it or use Hiltis if the foundation is good. Don't want to do that again. Bet you wouldn't want to do it at all.

    Bookmark   October 22, 2006 at 2:12PM
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To give you an idea of the cost Angelim Vermelho currently is sold for around 400 dollars per m3 FOB port, and ipe for 1300 dollars per M3 FOB port. It is very common species, but many times just left in the forest due to lack of market. The wood in reality is beautiful, if looks a lot like mahogany. If you translate the M3 FOB price to linear foot price in the States it is about half of what the landed retail sales cost is.

The end result would mean that this type of wood should be availble for about on third of the price of ipe.


    Bookmark   October 22, 2006 at 5:36PM
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O Man,,I am so usta seeing that up in the woods of Oregon only 3-4 species were considered marketable all the oak including Chinkapin,all the maple,any cedar but red cedar in fact I have seen them leave sound doug fir logs if they coudent get a full truck load all were pushed up and burned its a bad deal. Its all about money of course.

One third the price of ipe,thats about the same $ as preasure treated with out all the hassle and wonderment as to how long it will last. Ghesssss its a in a perfect world kinda thing but its compltley in range of what we have now to build these projects to last 100s of years.

There might be a way but even East Teak as big as they are has to look real close at the bottom line and marketing. money money money ghessssss J

    Bookmark   October 22, 2006 at 6:15PM
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Thanks for the input. We have approximately 80 species of trees growing in the forest that are suitable for lumber applications. But, only about a dozen are used for the most part. Under sustainable forestry guidelines you are allowed to harvest between 5 and 10 trees per acre depending on the size of the trees. There is a minimum tree diameter of 50 cms approximately and a maximum harvest permited of 30 m3 of trees per hectare, about 2.6 acres I believe. In a real good forest you might get up to 50 percent of this amount of high end trees, like ipe, jatoba (brazilian cherry in flooring), cumaru, muiracatiaia (tiger wood), and massaranduba. That leaves the other species which frequently are difficult to market. They are frequently used for railroad ties and there is some market for pilings. The dutch will take enormous quantities of this type of wood as I mentioned. They are the second largest importers of tropical wood in Europe after the French.

I am sure there would be a demand for a lot of the tree species we have here for outdoor construction, but that would take a company with enough presence in the States to market the stuff and have enough inventory to supply their market area. There are also great species that could be used for structural members instead of PT pine. Many of these are easy to screw into and a lot more workable than ipe. And, they are good looking when a finish is applied, something hard to do with PT pine.

I guess this is something to work on. Right now we have a challenge just supplying our dutch customer.


    Bookmark   October 23, 2006 at 9:18AM
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Well I'm still at the same point as I was on the 15th. I see alot of good ideas here and I will be using some gravel underneath the post and maybe a little on the sides before backfilling.

I've been wating for some help on plumbing the posts, neighbor had some work being done and the guy said he'd help me get the posts plumb, but that doesn't seem to be the case and I can't wait anymore. I see that it can be done with making sure 2 sides are level and then nailing a couple braces and then be sure to check checking for level while backfilling using the methods explained here.

I see where it was posted to be sure to either soak or cap the cut ends of the posts. I was told to just make sure that end went up but I like the idea of actually protecting it. The soaking method seems rather straight forward so i was wondering if they sell caps or if you buy the copper and then cut to size and nail?

    Bookmark   October 24, 2006 at 6:22AM
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I suggested capping the posts, as I had several that rotted from the top end grain. If you go to a decent hardware store or lumberyard you can get 16oz copper sheet for a few dollars per square foot. (16oz because it weighs 1 lb/sq.ft.) I also pretreated the cut ends but frankly don't trust that alone. The copper sheet is so soft that you can cut it with inexpensive metal shears and form it pretty easily with a hammer. It may not look perfect, but who cares. I have actually used an aluminum sheet metal break to bend it for window cap flashing - rented the brake by the hour at the local Taylor Rental.

    Bookmark   October 24, 2006 at 11:41AM
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I have a question, I'm building a 10x12 shed and I'm setting it on cement footers with 4x4s. The problem is I dug the hole and poured the cement in yesterday, now it hasn't stopped raining since I did it and the holes are completely full and the cement isn't cured. Its been 24 hrs and its still not hard. Am I gonna have to start over or will it be alright? Anybody please help!

    Bookmark   April 16, 2011 at 8:03PM
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