Concrete bag wall

Old 02-16-20, 06:04 AM
Thread Starter
Join Date: Dec 2004
Location: South Florida
Posts: 1,121
Upvotes: 0
Received 1 Upvote on 1 Post
Concrete bag wall

People make low retaining walls around culverts in swales by laying bags of concrete on top of each other, wetting them down, and leaving them until the bag degrades. I tried this once and when i peeled the bag off, the concrete was pretty crumbly. What is the trick to get this to work?
Old 02-16-20, 08:12 AM
Marq1's Avatar
Join Date: Sep 2016
Location: USA MI
Posts: 9,248
Received 1,099 Upvotes on 999 Posts
There isnt one, by not mixing the concrete your just allowing the exterior to absorb moisture forming a crust and nothing is mixed properly. It's just a cheap fast way to build something but it will not last!
Old 02-16-20, 08:31 AM
Thread Starter
Join Date: Dec 2004
Location: South Florida
Posts: 1,121
Upvotes: 0
Received 1 Upvote on 1 Post
I don't know, not to disagree but I took the dog for a walk this morning and counted 37 culverts with this type of reinforcement. None of them looked like they had crumbled the way my test bag did. All were pretty old with the bag long gone and a nice coating of black algae. Could they be quick mix or Portland cement or something else that is well-mixed in the bag?
Old 02-16-20, 09:16 AM
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 45,153
Received 740 Upvotes on 646 Posts
I'd think the longer the bag sets, the more likely it would harden throughout. Your test would have probably worked better if you left it alone for years instead of picking at it. It may never be as strong as a concrete wall but it does work.
Old 02-16-20, 09:25 AM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Posts: 26,187
Received 1,701 Upvotes on 1,525 Posts
Or you could be looking at sand bags filled with mixed concrete.

Wetting an entire bag or letting it absorb moisture from the ground can only result in a weak, low psi concrete. That's why concrete is mixed with water. Otherwise people would fill sidewalks with dry powder and spray it with a hose. LOL.
Old 02-16-20, 03:38 PM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 25,943
Received 1,759 Upvotes on 1,572 Posts
I've had OK results when placing bags of concrete mix under water in my pond. I think the difference is the bag gets wetted all the way through and remains wet during curing so it's about as good as it gets without mixing. For above water use I mix the concrete then pour it into sandbags and stack them while the concrete is still liquid.
Old 02-16-20, 06:01 PM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,498
Received 66 Upvotes on 61 Posts
Do you mean bags of cement which is essentially the glue that you mix with gravel go make concrete or concrete mix which is dry cement and gravel in a bag.
Old 02-17-20, 05:32 AM
Join Date: Feb 2006
Location: USA
Posts: 6,345
Received 60 Upvotes on 52 Posts
Using pieces of rebar to pin the bags together as they are stacked allows additional moisture to reach the dry mix.

Thread Tools
Search this Thread
Ask a Question
Question Title: