I set 8 posts in concrete yesterday. Today, I look at them and see half of them have developed cracks in the concrete, usually just one crack radiating from the post to the end of the concrete, looking from the top. Should I worry about this? Is this normal, or an indication that I didn't mix the concrete right?
It doesn't really matter much. The concrete is just there to fill up the hole you dug to bury the post. It adds a little ballast, but that's just a plus. Jever notice that the utility poles are now put in with expanding foam?
The first time I set a post I used a wheelbarrow to mix the concrete and was worried about getting the mix right. Now I just slop everything right in the hole and mix it there (mixing it around the post). I use 'quickcrete' from the home labrynth and never had a crack. I'm not sure what type you use but I don't think it's possible to mix it wrong. May take longer to set if you use too much water. I think Steve is correct that cracks don't matter though.
I'd be more concered with the posts rotting. If you buried the cement the post will rot right at the cement line. Better to level the cement above ground and taper it for rain run off.
My experience shows that concrete cracking occurs as the wooden post expands or swells from the water in the concrete mix. I normally reduce the effect by putting a couple of heavy coat hanger wire circles near the top of the wet concrete to hold it together as it sets.
Is it possible I did not use enough cement powder? There were no instructions on the bag, I think we mixed it 6:1. I later found the
1-2-3 formula, which would be 5:1. I used pre-mixed aggregate, my neighbor had a yard of sand and gravel mix that I hauled to my place, and we used 5 shovels of that and 1 shovel cement powder. It was a warm day when we did this, the ground was moist but not wet, and the area is shaded most of the day. I tapered the concrete so that at the post it is an inch or more above the ground, and it does indeed taper away from the post, and I used pressure treated posts rated for ground contact.I think the general consensus is to not worry about the cracks? The posts are most definitely not going anywhere, cracks or not. Will the cracks let in moisture that can shorten the post life? I don't know deep the crack goes, they extend from the post to the edge as viewed from the top, but I've not dug down to see if they run all they way to the bottom of the post.
Update on cracks - 48 hours later, half of them cracked, and the crack may be as much as 1/8 inch. on some of them. Just one crack, as if the posts did indeed swell up (what happens when the posts dry? will the then be loose in the cement?).
My bad - we used *six* shovels of aggregate and 1 shovel of cement powder.
(snip)
. I tapered the concrete so that at the
Shoulda set the post on a couple inches of gravel in the bottom of the hole, and then poured gravel a few more inches up the side, then used concrete over that. Even 'ground contact rated' posts should never sit in a pocket, with no place for water to drain.
Posts are pretty cheap, concrete is cheap. I'd just live with what you did, but keep an eye on it.
-- aem sends...
(snip)I use 'quickcrete'
Snerk. 'Home Labyrinth'. I love it.
-- aem sends...
Is it just me, or is 'premixed aggregate' the dumbest idea in DIY? I'm guessing the folks who order it are trying to save a delivery charge- but they'd be better off just buying redimix, IMO.
I've shoveled lots of sand, gravel, and rubble, and know that it is impossible to send a load of mixed sand and gravel someplace and have it arrive still mixed. Let alone drop it off a truck. . . let it get rained on. . . shovel it again. . . drive it someplace else. . . repeat.
Maybe someone who works with concrete everyday can adjust by eye, grab a sandier/stonier shovel full to adjust the batch in process. But the average DIYer can't tell too dry from too wet, let alone too bony from smooth.
A couple folks have mentioned this lately. Is it one part of the country that uses premixed aggregate- or is it common?
Jim
Maybe I should have bought redimix? I'm thinking the cracking was because I didn't use enough cement powder, and premixed concrete might have saved me the trouble. But what is done is done, and it's only 8 posts. I'm doing 20 more this weekend, and this time I'll mix it 5:1 instead of 6:1. But I already had the pile of aggregate, so all I needed was cement powder. I don't know who pre-mixed it or where it originated from. I got it from my neighbor 2 years ago, and he had it for a few years before I took it
Actually, I did set the posts on a couple inches of gravel. I dug the holes 33 inches, dumped in 3 inches of rock and gravel, and set the posts 30 inches deep. If anything, the crack will help drainage, at worst it will let water get to the post . I'm not going to do anything about it unless the posts become loose in the concrete, and I don't think that happens - the blocks are not split in half, they just have a crack on one side, as if the concrete shrunk as it set.
-snip-
I think I used the wrong term there- so just so we're both thinking about the same thing. I'm talking about the bagged concrete that has all the ingredients. They actually make one for setting posts. I think the difference is in type of cement- If I remember correctly it says on the bag- 'place post- dump in hole- moisten'. One bag per hole- simple.
Amen- It isn't brain surgery- and chances are everything will be fine.
For setting posts, it will probably be fine. The last guy I remember mentioning 'premixed aggregate' was doing a sidewalk. That's tough enough if your mix is good and consistent- but without knowing how much stone vs gravel you've got it is nigh impossible.
Jim
Yeah, we are on the right wavelength here. Dump in hole, moisten? Huh...haven't seen that, though I've heard others talk about doing exactly that. I would be concerned that it would not get wet all the way through, and that there would be dry pockets. Especially if the hole is deep, the stuff on the bottom might not get wet. I think I'd still mix it in a pan and then dump it in hole...
Ook wrote: ...
It will, eventually. Enough will set initially to hold the post; the rest will over time. Don't need any real strength for the purpose; all it does is fill the hole w/ a solid material.
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Its called NAVVY JACK (google)
replying to Zootal, Kevin Kirkpatrick wrote: Cracks will form from any square point to the edges. Easier installation is to set post and dump in dry mix and add water or let moisture from dirt surrounding hole take care of setting it up. You don't need concrete to ground level in my opinion
In my opinion don't worry about it. Even weak concrete is overkill for posts.
replying to Ook, Kevin Kirkpatrick wrote: It works and only want concrete below grade or it will rot off. The bottom foot is enough in the hole. I worked as an engineer
Probably okay for wood, disaster for steel post for obvious reasons.
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