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
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
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
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
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?).
. I tapered the concrete so that at 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.
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 <shrug>. 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.
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. . .
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
A couple folks have mentioned this lately. Is it one part of the
country that uses premixed aggregate- or is it common?
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 <shrug>
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
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.
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...
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
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