monopour retaining wall and footing?
Question for the wise and opinionated here: I have a 42′ retaining wall to build along with large piers for a deck (CMU columns will sit on the piers to support a second story frame of galvanized I beams and then a wood deck on that).
The retaining wall footing, as spec’d by my engineer, is 5′ wide and 24″ deep (our soil tests led to this result). That will be about 10 yards of concrete, or one truck. I then need abnout 6-7 more yards for all of the footings, and for the retaining wall, which is 30″ high (but the wall is 42″ high above the top of the giant footing).
I’d prefer to do this pour in one day. I’d rather pay overage hourly charges for the pump guy than to pay all of the minimums and travel time, etc. Pumping the concrete downhill about 145′ using a 3″ trailer pump (no overhead room for a boom). Concrete is the mix-on-site kind of truck, so I pay for what they mix on demand. Trucks hold 10.5 yards.
Any thoughts on this sequence: 1) I frame out the retaining wall form supported in place above the footing in advance, and then 2) pour the first truck of concrete into the footing; 2) let that set up for 1-2 hours, (and have the pump guy do whatever he needs to do to clean out his pipes in the interim); 3) have the second truck arrive and then pour the footings and then finish with the wall pour.
Having the concrete trucks come on the same day or on two different days will not represent any savings. I could save about $800 by having the pump come on one day and paying for a few hours of wait time. And I save a few hours of a couple of nicely-paid assistants. Not to mention, setting up 145′ of pipe and hose once rather than twice is desirable.
Biggest risk I see is that the form is a lot more difficult to secure “suspended” over the 24″ deep hole for the footing. Having the footing in place and then erecting the form on top would be a lot easier to set up and secure.
I’ve also not had any experience with asking a pump guy to do a pour, wait two hours, and pour some more. I suspect that will be met with grief, consternation, and perhaps refusal. If a 2 hour wait would involve ripping apart the piping, do a full cleanout, then setting it back up, I’d probably just do this on two separate pours.
Advice appreciated, as always. Thanks.
Replies
Don't wait
Although I've never poured a retaining wall this way, I've done it many times with stem walls. Make sure that the forms are well supported and braced. Pour the wall footings. You could add calcium cloride to this load of concrete. That would accelerate the setting. Make sure that the mix is not too wet. Pour the other footings then the wall. 30" is not a very high wall. Unless the mix is really soupy you shouldn't have a problem.
"Unless the mix is really soupy you shouldn't have a problem"
My experience last year pouring down the hill from the road where the pump sat was that I got a runny milkshake. Of course, it was also 33 degrees, so the cold and the downhil were two factors the pump guy blamed for the soup. And it was into an interior room where I had a lot less room for error. I'll be pouring this in April or May, outside, so more likely to be much better weather. Talked to the concrete company (also supplies the trailer pump) and He said I'd have 20-30 minutes maximum of "down time" for the pump before it would have to be torn apart.
One option would be to pour the footing, then pour the deck piers and wait 8-10 minutes between each pier (8 total), which would give me a good 70-80 minutes of letting the footing set up (without having to worry about too long of a wait where we'd have to rip apart the pipes, clean the pump, and then reassemble to pour again). Then I could finish the wall pour with some reasonable amount of stiffness in the footing. In the end, I might be able to do the whole thing in the four hour minimum for the pump, or an extra hour charge, rather than pay for two four hour minimums for the pump (and duplicate cleanout bags, and twice as much concrete cleanout ot haul away, etc. etc.)
cc is your best friend
Calcium Chloride is the way to go. Use the max in the first load.It's great for low temp pours. Since you aren't finishing any slabs you shouldn't have any problems. I did a slab once with max cc and we were walking on it in a couple of hours.