Dry Pour Concrete

This is the small-batch dry mix trucks in the Charlotte area:

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ronn47 said:
Read thru this and hopefully one of our civil engineers will stop by.
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The article assumes concrete is mixed with water the normal way... tough to infer anything about dry pour. Others have said what matters. It would be interesting to break up a small pad to see what actually happens. Removing the form to show that the concrete sets up all the way to the bottom is silly, since it is the edge.

Concrete is a hydraulic adhesive that binds sand and gravel together. Roman concrete was made from lime and volcanic ash. Modern Portland cement is made from calcinated limestone (calcium oxide) and sand.

The extremely exothermic (gives off heat) chemical reaction is called Hydration and produces cured cement (calcium hydroxide):

CaO + H2O → CaOH2+O

In all reactions, the way to drive it is to add things to the left side of the equation. Therefore, excess water works in favor of complete conversion. Dry pour does the opposite. I imagine that it doesn't matter as much in small volume pours, but it most definitely matters in larger pours.
 
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9outof10mms said:
There are dry mix trucks that show up on site and mix exactly what you need. However, they mix it in a hopper, not on the ground. For small pours like this one these trucks make sense as you don’t typically pay the short run penalty (typically $500 for anything under 3 or 4 cubic yards on a normal wet mix truck). Yes you pay more per CY for these guys but it ends up cheaper than a normal truck.
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Or you could, you know, mix the stuff in the bag. They even print instructions on it. Home Depot will rent mixers and everything. https://www.homedepot.com/c/concrete_equipment_rental#mixers


I don't see any advantage to this method and a whole lot of disadvantages.
 
GoWolfpack said:
Or you could, you know, mix the stuff in the bag. They even print instructions on it. Home Depot will rent mixers and everything. https://www.homedepot.com/c/concrete_equipment_rental#mixers


I don't see any advantage to this method and a whole lot of disadvantages.
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Ordering a dry mix truck would be for something 2-7 cubic yards that you need relatively quickly/at the same time, in my opinion. A regular truck is going to hit you with short fees ($500-ish) being under 3 (some of them are under 5) CY's. If you're doing a driveway extension that you want poured in one round, then this would be great. Or a short sidewalk job (20-60 feet or so).

Or, the "regular" companies are sometimes too damn busy for little peons that don't order by the hundreds of CY's, so the dry truck might be your only option at times. Good to have options.
 
Carolinatlc said:
I'd love for someone that actually understands the curing of concrete to chime in. I've never seen it done that way before. I'd be interesting in trying it for a pad under a shed roof I built off my shed. No real loads other than my mower and maybe a UTV. I dry poured the posts for it and have done it several times for fence posts that seem to be really solid.
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It's not about curing--it's about getting enough water to every bit of the mix. Curing will happen (to some degree, depending upon the amount of water added) regardless. If you leave a bag of cement mix out in the rain, it'll "cure." It won't be the world's best concrete, but it'll react.

Dry pouring a post is different than a slab. A post pour is predominantly trying to add weight to keep the post anchored and straight. Pretty much no risk of failure (if it cracks, who cares, as long as it stays relatively in place). There's zero worry about aesthetics (it's underground). Lastly, the water application is roughly controlled so you can get close to adding the correct amount (or at least enough to guarantee enough conrete mix got wet. By that I mean it's a hole, so the water can be poured in and puddled to a known amount. The bag says to fill the hole to a certain depth and let the water sink in. You can't do that with a slab--you have to "shower" it which is absolutely zero control over application rate or amount.

The best way I can describe the problem I see with dry mixing a slab is when you mix a bag of concrete the right way in a wheel barrow, think of how hard it can be to get the water dispersed equally in that controlled environment. You typically have to add a little more, mix it more, and then you STILL uncover a pocket of totally dry mix. Now think of all the pockets of mix that are underneath a stone, that got pack tighter than other areas (which encourages the water to infiltrate in another direction toward looser material), etc.

This is a corner best left un-cut.
 
9outof10mms said:
Ordering a dry mix truck would be for something 2-7 cubic yards that you need relatively quickly/at the same time, in my opinion.
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I think the video mentioned they used 13 bags or something. Once you've carried the bags to where you're going to put the concrete, the hardest part is done.
 
GoWolfpack said:
I think the video mentioned they used 13 bags or something. Once you've carried the bags to where you're going to put the concrete, the hardest part is done.
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That's the other thing: how NOT FAR those bags go! You need semi-truck shipment to pour a little pathway or shed slab!!!
 
9outof10mms said:
That's the other thing: how NOT FAR those bags go! You need semi-truck shipment to pour a little pathway or shed slab!!!
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If I remember right it was around 8-10 bags just to put our basketball goal in several years ago. They definitely do not go far. I'm just going to pay the man for my job.
 
90 of the 80# bags to dry pour a 9x18 spot if you’re wanting 4” thick.
 
BigWaylon said:
90 of the 80# bags to dry pour a 9x18 spot if you’re wanting 4” thick.
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Myeahhhhh…I’m gonna go ahead and say “call a truck.” Mmmkay? Thanks, Peter.

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beamernc said:
That's only 7200 #. Multiple trips to Lowes.
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$79 delivery fee. Well worth it just to not to have to load them into something and then unload them.

(Yes, I put them in my cart the other day just to see what my options would be)
 
I ran into an old fellow I know in town who has been in the concrete business for about 50 years. I asked him about dry pour for a driveway/ parking pad. After he stopped laughing he said you could call him to clean up all the cracked sections and pour it correctly. He said dry pour works great for posts but that's all. He says there is no way the water/ concrete ratio could ever be correct by misting water on the top. He also said up here in the mountains a slab would have to be six inches with mesh to survive frost heave.
 
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9outof10mms said:
That's the other thing: how NOT FAR those bags go! You need semi-truck shipment to pour a little pathway or shed slab!!!
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I purchased a pallet of 80lb bags to do a 8x8 spa pad. Used a mixer and dumped into the form over and over. I think I had maybe 4 bags left over. My FIL and I mixed, poured, and finished the pad.

NEVER again. I’ll gladly pay a small batch fee and have a truck come next time.
 
I throw whole bags into the holes that my dog digs under the entrance pad to my building. Then cover it up. Punched a few holes in the bag. It'll be harder than what she wants to dig on. I mixed it so it would run under the steps of the deck. She hasn't dug that part up again.

Those big trucks you see spinning going down the road, they spin for a reason. To mix every think. There's a certain amount of rotations that have to be completed in order to mix it correctly.

But hey, spend your money however you want to.
 
And I don't understand the point of having all these women folk in spandex working concrete or pushing sawmills. Oh, wait a minute, yes I do. Most men are just like me
 
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DC Bigdaddy said:
And I don't understand the point of having all these women folk in spandex working concrete or pushing sawmills. Oh, wait a minute, yes I do. Most men are just like me
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There is a woman on YouTube who splits wood in a sports bra and yoga pants. Fascinating.
 
I’m waiting for a video of Dylan Mulvane working concrete or splitting wood. The “stew shot” I can do without. 😂
 
Jeppo said:
I’m waiting for a video of Dylan Mulvane working concrete or splitting wood. The “stew shot” I can do without. 😂
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Better splitting wood than getting it.
Rather see firewood than the twig and berries.
Wonder what he's done with the stump?
Probably looking for a place to hide that log.





Ok I'm out.
 
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