Concrete mixers

[Lopez]

I'm putting up a 25x40x12 high shop and was quoted $12,000 for the concrete work. 12x6 footings, 6x24 stem walls, and 5" slab. This was the only quote I could get since there's so much construction happening, relative to available labor. I figure there's $4k to $5k of materials, so I've decided to do the work myself. It's owner built, exempt, so there's no inspections what so ever. Anyway, my real question is about concrete mixers. The two sizes I'm interested are the 6 cu ft (1 bag), and the 9 cu ft capacity (1 1/2 bag). Does the 1 bag mean 1 cu ft bag of cement mixed with 2 sand and 3 gravel equals the 6 cu ft capacity? Is the 94 lb bag of cement equal to 1 cu ft? One last question: I've noticed 2 types of mixers. One is the traditional one with the large ring gear all the way around the O.D. The other is with barrel mounted for & aft, the axis in the same direction as the motor. Near as I can determine, this type is for grout, plaster, and mortar only. Is that correct? Thanks much for any help.
Don

[harleymsn]

You jobs sounds like you will uses in excess of 20 yards of concrete. I think you will find that it is really more cost effective to get redi-mix delivered as opposed to mixing it yourself. I'm not sure what you mean by 'stem walls' so I cannot accurately calculate the amount of concrete needed. As an example, this past May I poured a 5 1/2" floor in my 30x50 pole barn. I did all the prep work including 4" of 1/2" chip (limestone) and 6mil plastic for a vapor barrier. We used fibre in the mix as opposed to rebar and a 4500 psi mix.
We used 22 1/2 yards ($2026.00). I hired a local finisher who did a beautiful job, his rate was $.40 a sq ft ($600.00)
I would get another quote or two, but if you still decide to do it yourself, compare the redi mix prices with the material and mixer cost to do it yourself.

[rfawkes]

I used a mixer and poured and 8 X 16 pad 4 inches thick, and it liked to kill me. Hire it out. I didn't save any money, and my back was sore for a week.

[GareyD]

Small mixers are real convenient to have around the farm...great for repairs, corner posts and smaller project....

Personally if it is anything bigger than a short walkway, I'm gonna have the boys in the big trucks haul it out for me [img]/forums/images/icons/wink.gif[/img]

[Pat]

With a small mixer (the largest you mentioned is a small mixer) you WILL get a series of cold joints because you will NOT be able to mix quickly enough. Even if you could the mud will kick off before you get to work it. Even with helpers this is nearly an impossible task... U_N_L_E_S_S... you make a segmented pour. Put forms inside your perimeter forms to segment the floor into, well, SEGMENTS. Make them rectangular and of a size that you can pour from multiple mixer loads before it is too late to work what you have poured.

My little electric mixer just barely does three 60lb bags of redi-crete at a time (about 2 1/4 cubic feet if I recall correctly.) Anyway it does about 200 lbs of concrete (3 ea 60 lb bags plus water) and fits in a couple 5 gal buckets. At 5 inches thick that is about 2.4 sq ft of floor area. I would need almost 7 batches from my mixer to pour a 4x4 foot section of floor. Pretty tedious but definitely doable, expecially in cooler weather with slower cure rates. If you put holes in yoiur reusable segmenting forms you can have rebar stick out to tie to the next segment.

I have had fiber in place of rebar before and now only will accept or recommend fiber when it is in addition to rebar (or other steel like wire or whatever.) Forming is a bit more of a challenge but hexagonal segments are really nice.

To make your stem wall easier, consider using knock out blocks (bond beam blocks) and 100% grout them. This IS something you can do with a small mixer. I have built 6 ft high fences this way as well as my mom's safe room (8ft walls.) I did NOT "lay" the block, i.e. butter the joints with mortar but instead "DRY" stacked the blocks and then 100% grouted them. I use small pieces of gravel to true the dry stacked blocks checking plumb and level as I add each block. I use both vertical and horizontal rebar in the blocks. Dry stacking takes a lot less skill than regular block laying and if you grount them 100% the final strength result is as good as the best block layer could do.

If you want to do the floor in one monolithic pour... call the redi-mix truck and have a crew there to assist in working the mud. Make expansion (control) joints no further apart than 8 ft. All concrete cracks. To control cracking is important. Joints help. Fiber only in a large monolithic pour will most likely result in cracks that the fiber will not hold together. Add some steel so that after the floor cracks, the cracks will be held together and not spread open.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]