Got a little addition to do at the local natural gas utility. Needed a fill in job while waiting for the permits and such for the big box hardware we are off to do next. One of the other supers started it and then was moved on to a condo project. He got footing and foundation walls poured for a 500 SF addition, but didn’t strip them.
What we found was the some of the ugliest concrete work from a contractor I’ve ever seen. Poorly vibrated, out of square, anchor bolts for structural steel off dimension and location by as much as an inch. We found four different types of screws in the forms, and I think even ONE type of screw in formwork is too many.
But worst of all, he did the dreaded monolithic foundation: footing and wall poured at the same time. That has to be the most ignorant, sh!tty way to form that any fool ever came up with. Stripping was a nightmare because the footing concrete had bubbled up around the wall bottom plates and effectively locked the wall forms in place. Those plates had to be pried out with a big wrecking bar and came out in shreds. It took 2 guys a day and a half to strip 70 LF of “Strip EZ” wall and footing. And of course there are still 2×4 cleats embedded in the wall that will provide a fine meal for the local termites.
The ground here has a lot of rock in it and stakes are difficult to drive, so footings can be a bit haphazard. Knowing that, why would anyone want to build a wall on top of said unstable footing form? The result was predictable: the footing forms moved from correct elevation during the wall forming process and of course the finished wall is up and down an inch each way.
The final insult is that there was no good reason to do this, because the whole thing is accessible for the concrete truck to place directly from the chute. Neither wall nor footing pour would have required a pump. And the job is 2 blocks from the ready-mix plant, so no inconvenience to do 2 separate pours. Aaargh. I hate inheriting someone else’s crap and expected to make it all turn out OK. The project manager took a look at the stripped product and got on the phone to the other super and chewed him out royally for such unprofessional work.
Now I’m guessing that I’ll get a reply or two with claims of many years of successful monolithic pours. And I’ll admit that there were poor practices evident in this work regardless of the forming system used. But I’ll stand by my opinion that monolithic foundation pours should be avoided and are the mark of the hack.
Wally
Replies
You won't get an argument here.
We use them only as a last resort, usually involving cost. The weight of the concrete always causes the ooze at the bottom which buries the forms.
Bummer.
carpenter in transition
Monolithic is pretty much the standard for residential construction in my area. Its the only way I've ever done it. But I can change..., I swear! Tell me why I should.
Mono is ugly as hell and offers way more problems than the supposed cost savings. Just because it is the typical way it's done locally doesn't mean it should be done that way. The two biggest problems are form instability and embedded wood penetrating through the finished wall.
In a mono form, once the footing is elevated and straightened, wall forming begins. That means bottom plates nailed down into the footing cleats, and the pounding can easily punch the footing elevation down out of level. Once one side of the wall form is stood up, pour height is shot onto the form and some sort of pour strip attached. Any other downward pressure on the form during the remainder of the forming process will cause a low spot in the finished wall, which translates to framing problems. Similarly, any lateral movement in the footing stakes results in a wall that is either out of position or out of plumb. Neither is acceptable. Do it right: pour a footing first and then go back to the batter boards for really accurate wall layout.
The aforementioned cleats remain embedded through the walls, and will eventually rot out and allow moisture and ground water into the building interior. The wood below grade is also a fine enticement to termites.
Rebar system for both wall and footing has to be suspended from cleats. Tying it like that is a PITA. If the engineer is obsessive about the strength of the wall-footing joint, keyway and dowels hooked into the footing will be more than acceptable.
Finally, because of the open footing outboard of the wall form, wet concrete will come up and out of the form. Typically in situations like this, crews minimise vibration to prevent too much concrete coming out at the bottom. Bad move - it's easy to leave honeycomb as a result of too little vibration. The solution is to vibrate as thoroughly as with a normal form and then scoop up all the excess later. Even better, avoid this crappy forming system altogether and do it properly. The savings are so minimal, and the downside is formidable.
If the site requires a pump for both footings and walls, then the wise contractor accepts this and allows for it in their pricing. Professionals won't accept this short cut - it just costs more later.
Wally
Lignum est bonum.
Edited 2/7/2005 9:03 pm ET by sly_karma
the way we do it is compact the soil real good then dig the footer. remember we only need 18 inch deep footer. then we metal form on top of soil. metal forms are 10 inches held with pins, pour in morning pull forms that afternoon.
Why so many string lines crossing the forms? Never saw that before. Screeding guides? Trip wires?
Monopours can save time and money, and give professional results. But they have to be done right. And using plywood cletes/spreaders is a cardinal sin.
They ARE trickier and require more attention when setting up AND pouring. No question about that. But once you develop a good system to combat the problems, you know when to use seperate pours and when to use a monopour.
There's a time and a place for everything.
That's not a footing, that's a grade beam.....
The forming and pouring technique that I use is different but similar to the one you describe here but is one that takes into account most of the problems you are talking about. I think your just kind of describing bad work in general. Leaving any wood in the concrete or the ground is not something I do. I generally use metal wedge ties to tie the forms together and to hang the rebar off of. I set metal stakes to a line first and then hang the form boards from the top down. After the outside forms are up I tie up the rebar and lay it in the footing and hang it after the inside forms are up. Concrete will blow out from the footing if your not paying attention but I almost always pump the footings first and then come back and do the walls after the footings have set a bit. I have seen concrete blow out from too much vibrating but once again you have to pay attention. Having a pump is key for sure and I've learned to ask for certain guys with the pump. Experience pays!
I only do one or two foundations a year but every time I form one it seems like I'm spending inordinate amounts of time on it. Which is why I'm willing to consider any other alternatives. My experience with subbing out foundations is that concrete subs havent been as careful as I am. Building on a bad foundation is extremely aggravating and time consuming.
Tom
Tom, any chance of a photo of your formwork?
I have a small wall coming up that would be nice to mono. I've never suspended a form. Only poured footings and later set forms. Every experience I've had with a pump was horrible. Bought a crane just to avoid pumping.
Last time around, after all my bellyaching, the guy in charge of the whole state came out to supervise the pumping. Still came out with voids I wouldn't have had with a chute or bucket pour. Nobody vibrates but me, that wasn't the problem.PAHS Designer/Builder- Bury it!
I've only recently joined the digital age and have very few jobsite photos. I got some great vacation shots if your interested though. Sorry.
Tom
Still came out with voids I wouldn't have had with a chute or bucket pour. Nobody vibrates but me, that wasn't the problem.
I've pumped many thousands of cubic metres of concrete over the years for thickened-edge slabs, suspended slabs, columns, walls, curbs, stairs, tilt-up slabs, beams, pre-cast members, footings, cylindrical tanks, you name it. I can't think of an instance when I've seen voids and honeycomb that weren't the result of improper vibration practice. Certainly voids are not the result of placement mode. It's what happens after placement that matters. If anything, a pump can help to direct more concrete into difficult spots, such as underneath a window buck, that vertical chuting cannot reach. We would only consider crane-and-bucket placement if we were too high for a pump to operate effectively. Only then would we resort to the much slower placement rate of the bucket - and we have dump buckets that take a metre at a time.
The most typical cause for voids is vibration at intervals too far apart. Determine the vibrator's zone of effect by careful observation of the vibrator in the form, then make sure that the next placement of the vibrator overlaps slightly into the previous one. If the pump nozzle is progressing too quickly, it is very tempting to catch up by making each vibrator placement a little further apart, but the poor results are not worth it. Slow down the pump rate so that the vibrator operator can keep close by the nozzle without compromising quality. Also, remember that surface voids can be caused by too much vibration as well as by too little.
When my crew uses a pump, we take control of it. As the customer, you have the right to direct the operator exactly as you wish - within the limits of the machine and its surroundings, of course. Typically I put the most experienced member of the crew on the nozzle and do the vibration myself, although on work that won't be visible, I may take the opportunity to let other crew members gain experience on the vibrator. Before we commence the pour, I explain to the pump operator where we want to start, which direction we will proceed, and how many lifts pour will have. Many operators will crank the pump rate up as high as possible, but again, at $200/hr you have the right to ask them to reduce it to a rate that the vibrator operator can keep up with. It's certainly not worth saving a few bucks on pump time if things are going so fast no one can keep up.
Sorry if I come across as preachy, but blaming the pump for voids ain't the way to go. Some complicated situations call for different solutions but for most residential work placement is pretty straightforward.
Don't compromise wall accuracy by pouring it with the footings. Since you no longer rely on a pump, doing it in two pours shouldn't be a big deal.
Wally
Lignum est bonum.
Sly, thanks for the thoughts, but as I said, it ain't the vibrating either over or under. I'm the only one I trust to do it. You aren't the first who's said there shouldn't be inferior concrete, but that's what I've gotten all 7 times I've pumped, 7 different operators. These aren't surface voids, but major voids under blockouts and (less so)in corners. Separation of aggregate is clear. Out of a chute or bucket, no voids. I have 2 vibrators and know how they work. I'm also picky about slump.
My conclusion is that smaller pumps dropping the mud shorter than the 60-70' I see might very well be the solution, but those pumps aren't available here. I'm not shy, or too cheap, about telling the operator to slow it down. There's nothing I can do about the drop height. The guy in charge of sales here (30 yrs experience), who supervised the last pump on the walls with us assured me I had a great product. Wrong.
I figure ~$750/pump and get a crappy product. Crane looked great in comparison.PAHS Designer/Builder- Bury it!
Tom,
Whilst I'll certainly agree that I've inherited some low-quality work overall, there are problems with mono pours that can only be resolved by inordinate amounts of time and bracing. Any work that is in the ground relies on stakes, and stakes can't be relied upon for accuracy of elevation or location.
In a typical strip footing I use a stake every 4 ft and take care not to step on the form or nail downward into it so as to avoid messing with the elevation. If I was to form a wall on top of the footing, I would double the number of stakes to keep it from dropping during the wall forming process. That's a lot of extra work.
In addition, for the wall to run dead straight, the footing must also be perfectly straight, necessitating lateral braces that wouldn't be needed in a regular footing pour, not to mention needing a much wider excavation. Much easier to pour a quick, simple footing, strip it and then snap straight, accurate lines on top. And the footing is stable for elevation too.
A mono pour is like forming a concrete curb: finished work that needs to be accurate for line and elevation but has to rely on stakes for anchoring. Yes it can be done, but curbs are extremely time consuming when considered on an hours-per-cubic-metre basis. In the end, a mono pour either gives crappy results or wastes more time than it saves.
Just Say No To Monolithic Forming.
Wally
Lignum est bonum.
Thanks Wally. I'll be calling you for my next one!
Mono is fine , especially for small jobs like this where another trip with the crete truck is cost prohibitive.
But you have to think, plan, and work sharp.
Remember a hack can do any kind of job poorly, even a condo project
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Piffin,
We don't get charged a delivery flat rate, just straight per-metre rate, so there isn't any cost saving to be had by combining two pours into one. I'd be interested to see a list of situations where mono offers genuine cost savings and still yields accurate finished work.
Wally
Lignum est bonum.
"I'd be interested to see a list of situations where mono offers genuine cost savings"
Here in Western Washington we pay 250 every time the line pumper comes onsite.
We also pay about a 10.00/yard upcharge for any order under 4 yards.
So say I'm pouring a small addition that I can't get a chute to and don't want to wheel the mud from the alley. Say I need three yards for the footing and another three for the wall. I'd be saving 60.00 on mud and 250 because I only need the pump once. Let's say it takes me an extra hour to set up and an extra hour to strip at 50.00/hour. I still save 210.00 on that little pour. Plus, I get it poured all in one day which can help with tight scheduling, especially if I (and any help) commute an hour each way to the jobsite.
Oh, yeah, I guess I'd better say that we regurlarly pour 24" tall walls here in the temperate Pacific NW. I'd be real hesitant to pour anything taller than that monolithic because of the weight of the concrete in the wall.
That's one instance.
Last time i poured mono it was close to six yards total. I think between 1-1/2 footings and 4 wallsIt was for a small porch. I live on an island so each load is going to cost a min 250 to get it here.Add waiting time for line up at the ferry. Additionally, the owner wanted the job done in minimal time. Access was good, back right down the drive and dump. Yeah, it si a PITA to form right and be able to srtrip it again , but compare that to the extra five or six hundred bucks and couple of days in the schedule to do it all in normal steps. We had striped the forms again and were building the porch the day we would have been pouring walls in a twop step process.It might have cost an extra four or six hours to form.
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around here on pump truck they charge, per mile to job, per hour on job and per yard pump. combined. so a 400 yard pour is about $2200 but thats a 300 meter boom truck
thats a 300 meter boom truck
You wanna verify that numer Brownie? 300 meters is a Texas size boom, and you're in a different state.
I'm sorry, I thought you wanted it done the right way.
If I use a pumper along with the dumper, it adds about $800 to $1000 per day to the cost of the job, whether it is ten yards or a hundred
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"I'd be interested to see a list of situations where mono offers genuine cost savings and still yields accurate finished work."
I've got one...
Any time you're working under an existing building, you can do mono easily, and it's faster and just as accurate. The key is to hang the wall forms from the building. Form the footing in the trench as usual, and set the rebar. Use metal spreaders, not wood, or brace the forms to the outside and leave no spreaders in the pour. Then, drop temporary 2x legs from the building and hang the wall forms from them, just above the footing. Pouring a stiff mix minimizes the amount of spill from the footing form, and a quick go-round with a trowel to get the excess off means no form boards will be trapped. We pay for pump and standby time, so doing one pour is always a lot cheaper.
I've got some photos of the last time I did this... somwhere...
Dave,
I'll pay this one. I've done something similar before.
Piffin as well has a situation where there are significant non-forming costs that make reducing the number of pours advantageous.
SamT, was the school fdn required to be mono for earthquake or something like that?
Most of the other reasoning falls into 3 broad categories:
job too small to justify pumping twice
larger jobs where the footings can't be tailgated
that's the way everyone does it around here
Solutions seem simple enough:
small jobs are usually easy to wheelbarrow - and should be less labour required than the extra time to make mono pour work accurately
contractor should recognize this situation in the pricing stages and allow for two pump rentals
you're on BT to learn something, right?
Anyway enough from me and my soap box. Hope everyone is having a good week. Mine is confusing. The gas utility job goes on, we are grading and forming a couple of small slabs plus I am also running back to the dental clinic job to finish off door hardware. Tough to make the adjustment from ground work to finish work a couple of times a day. And of course then phone keeps ringing...
WallyLignum est bonum.
Sly
>>SamT, was the school fdn required to be mono for earthquake or something like that?
Dunno.
I was hired off the street to do the excavating, forming, and hiring. Took the plans and ran with it. The regular foreman poured as I was finishing the last 100' of forms.
I said it was a fast system.
SamT
Sly,
Had to do a monopour for a school foundation in California. Footing was 2'x2', stemwall was 12" high and 8"-12" wide, I forget.
Any way we used these neat form suspender bridges consisting of 2 stakes, an adjustable heigth crossbar and two sliding 'wings' on the crossbar that the forms were nailed to.
The bridges were placed across the footing trench 4'OC after the steel was in, then the forms nailed to the 'wings'.
Check and adjust everything after all nailing and pounding. No penetrations into the footing. Easy to clean excess mud from the bottoms of the forms.
SamT
Sam, got any info on this system?
David,
Sure don't bubba, I only used them that one time. But, IIRC, that system or something similar is required in CA. for all school foundations and maybe for other civil defense type buildings. NO penetrations into the footing, ya know?
Googled "form hangers concrete"
Adjustable hangers :: dee Concrete Accessories
http://www.janell.com/products.html
http://www.daytonrichmond.com/products/flatslab/menuformhangers.html
This is the one I used;
http://www.decristo.com/concrete-masonry/concrete-accessories-form-hanger-school-bracket-52.shtml
Wound up searching for "+concrete accessories hang form".
They're called Fast-Set form hangers and they are fast.
With a row of snap ties at the bottom I'ld feel confident with these and a 2' stemwall. Maybe some bracing. Come to think of it, I'ld want snapties at 18" high stemwall, belt and suspenders.
SamT
Down south (Texas) monolith is about all they do for residential. No freeze line to speak of here. It does bring up a question I have. I have always heard you should put rain gutters on a house and get the water away from the foundation. Is that more for houses with basements or does this apply to slabs as well? Does proper grading accomplish the same thing?