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Old 09-22-2017, 01:55 PM
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Default A question for DDA52

I was asked this morning by a friend the following.........

"Just how much of a slab can one pour using a 3 bag small mixer"?

He's wanting to pour a 4" slab for a 10'x20' shed off the back of his shop and was wondering if it could be done using bags of premix.

I've done smallish slabs like 8' x 8' for a pump shed, but nothing as large and as thick as he's wanting.

He's telling me he can get all of the bag'd mix he can use for half over the counter pricing and would want to do so.

Can, could he use a sectional screed temporary in place till the next batch is ready to pour, pull out the temp wall and press on to the next etc etc etc.

I can see he'd have to notch the wall to allow it to sit onto/into the steel mesh etc to keep things somewhat level as he went so sagging of the pour to not run or sag too much on an open end.

Something I've never thought much about before.

In addition, just how much time can lapse between one pour to the next before a decent bond between pours degrades?

When pouring a new piece of pad to an existing slab will there be any adhesion from the old existing slab to the new freshly poured pad? Other than the use of pieces of re-bar to tie one into the other.
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Old 09-22-2017, 05:31 PM
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If he can mix a batch in 10 minutes that is 18 cf and hour, at 27 cf per yard and just shy of 7 yards for the pour means it would take over 8 hours of mixing. That means the slab cure would be spread over 8 hours going from one end to the other. What a nightmare that would be to a finisher.
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Old 09-22-2017, 09:25 PM
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He heeds a bigger mixer and more help.
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Old 09-24-2017, 09:34 AM
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Sorry so late, been busy again.

Yeah, it can be done, but like milo said, it will take forever and be a nightmare. They do things like this in 3rd world situations because there is no other way. Its all they have and the end results look horrendous, too. I would NOT recommend it at all. You aren't saving anything at all and will get a bad product to boot.


Actually, the best way to do this is all wet screeding. Putting in a rigid form will ensure a crack at that point due to the cold joint if its allowed to progress that far and my hunch is it will happen. Its just too much mixing time for a set not to happen at the form line. No forms would allow everything to blend together a little better. Still may have the cold joint issue. Its not a huge amount of yardage, but its enough. If its done in the winter, the cold will help slow it all down enough to keep it workable longer, but the total finish time will be tripled...or more. Lights will definitely be needed.


As to how long between...that depends on the temp and how dry the mix is. We have left stuff like that for several hours and not had it go bad. Its risky for sure and not something you want to make a habit of, but it can happen. Usually, as long as its not "dry" and semi workable, meaning, you can still mark up the surface and hopefully even work it a tiny bit, then you are still good. As long as its chemically active, it can bond.


As to the old work to the new, the only way to bond them is doweling. There is no chemical reaction left in the old stuff to cause it to bond and the reaction in the new by itself is not enough. There will always be a crack there. The dowels will hopefully hold it in place, if done right, so there is no separation or heaving. If aesthetics are an issue, you can always grind it out a bit and use an elastomeric sealer to hide it. They make leaveout strips for this.
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Old 09-25-2017, 06:28 PM
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I looked at what he wanted to do this past weekend. This is the same neighbor that has the Differential/rearend pto posthole digger.

His mixer is a little smaller than mine, said he got it from HF.

Even if we had 2 mixers I told him it was more trouble to get a nice finished surface for his little shop addition.

He called today and got an estimate on getting a truck for the pour and is also going to add a pad outside the door.

I offered him my help with setting up the forms and leveling, but added it would be more of a "I'll show you how to do it sort of help". I'm still not up to that large of a project.

Thanks for the inputs guys. Good information all round.
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