I get this question a lot from customers that have an installer doing their fence. The installer walks up to a post hole, tosses in a bag’s worth of dry concrete mix, adds a little water on top and claims it will set on its own below grade with the moisture from the ground. So, the questions I get is ‘that the proper way to do it?’. The short answer is ‘no’.
Any concrete producer will tell you that it should be mixed wet and then poured. Concrete trucks drive around with mixing wet product for a reason. Think of it this way. You can toss eggs, milk, flour and sugar into a cake pan unmixed, cook it and get something that sort of resembles cake. However, its realistically going to be a few cakey spots with blobs of dry flour and sugar. Whereas if you mix it, the cake comes out evenly cooked (and probably tasting a lot better). So, the short answer is:
MIX AND POUR YOUR POST HOLE CONCRETE
Now, I can already hear folks crying ‘FOUL’ on me steering you from the dry-bag method. I do agree that the dry-bag method will mix to an extent and hold. Your fence posts are not going to fall over with this method, but you will never know until a problem surfaces.
I have dug up obvious dry-bag post footings. You will find a solid concrete top, but as you pull it out of the ground, the lower portion is probably going to be drier and brittle.
As for the whole ‘it will wick moisture from the ground’ in the dry-bag method, that is true to a certain extent. Once that outer surface hardens, water is probably not going to get a whole lot further in. It also depends on how wet your ground is. I know its so dry up here in Ohio that my yard is cracking in places. So there is probably not a whole lot of moisture for that cement to absorb until enough rain fall penetrates down there. Given the rain fall this year, that isn’t something I would want to chance waiting on!
So, when in doubt, MIX AND POUR your cement. That is how the concrete producers envision it being used and its what we advise here at Iron Fence Shop® as well.