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Definitions "mono pour" vs "stemwall"

rl36's picture

Ya I'm a dummy. Originally from knots. So be it. Could someone clearly define a mono pour and or an additional stemwall "if necassary".  I much appreciate the help. thanks rl36

(post #61647, reply #1 of 39)

if this is in a contract proposal, the contractor should define those terms for you to avoid mis-communications.

In general, Mono means one - singular. a foundation is a monolithic pour when a slab is poured with a thickened edge so the footoing is incorporated into the slab.

In areas where a mono is inapprpopriate for various reasons, a footer is first poured, then a stemwall, then the slab sits on it and the compacted infill material.

 

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(post #61647, reply #2 of 39)

"Stemwall" and "mono pour" are not mutally exclusive terms. 


Here in the Pacific Northwest "stemwall" is the term we use for the foundation wall in an inverted T footing/stemwall type foundation. 


Now, if you were to form and pour the footing and stemwall together, instead of as seperate pours, that would be called a "monopour".  So would the way piffen said, when pouring a thickened edge slab with short stemwalls for a garage for example.  Basically to differentiate pouring concrete once instead of twice, or three times as many people do (footing, stemwall, slab). 


Monopours can save a lot of time and money, especially on small or remote pours where a pump is required.


 

(post #61647, reply #3 of 39)

Thank you 2   4   your explanations'  I am in the Pacific N.W. in fact right on the coast.   rl36

(post #61647, reply #4 of 39)

Where at?

 

(post #61647, reply #5 of 39)

That very difference in usage between you and I is why I was suggesting that it is best for the local guy to define his own terms if this is a proposal.

 

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Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
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(post #61647, reply #6 of 39)

Yes I hear you piffin on allowing the local guy to define necessities. Blodjett, Yachats Oregon is the place. It took me 50 some years to make it back here as a resident. Actually I do woodworking, thus the Knots referance. I am indeed building a garage/shop.  (SHOP) if you know what I mean. I want to have an understanding of the terms of concrete work to at least be able to speak the language. Thanks all for the info.  rl36

(post #61647, reply #7 of 39)

I dont reccomend a "mono pour" for the garage.  All Mono pour garages will get a big crack down its center. 


The problem with mono is that you cannot compact the dirt around its perimeter well.  Also its hard to pour a level  base for the mudsill and then slope the slab to drain.  All the mono pours, when demolished, show a gap between the dirt and slab


Best way, not the cheapest, is to pour the stem walls first.  Frame up the garage, and compact the dirt with compactor and/or vehical tires.  No steel is needed  for the slab if the dirt is compacted.  Do not tie the slab to the stem walls with steel, just use foam or jute batts for joints to stem wall, so the slab floats.  Pouring the slab under the shaded roof of a garage will have less cracking if poured continuously.

(post #61647, reply #11 of 39)

" All Mono pour garages will get a big crack down its center. "

I really wish you hadn't used the word "All"

I built a 28' x 44' garage that will be disappointed to learn that it does not exist.

But as a general rule, I agree that it is much mor dificult to deal with some things. For instance, I can't get it thru my poor little head how these guys can pour a footing and stem wall in a single shot myself. It all depends on knowhow and prep work.

To do a good mono slab, it takes a lot of compaction first and then the right mix so it doesn't shrink, along with plenty of steel.

Oh yeah, and deal with drainage....

 

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(post #61647, reply #12 of 39)

I built a 28' x 44' garage that will be disappointed to learn that it does not exist.


I have to do it Piff..


Invisable materials????



Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming....

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(post #61647, reply #13 of 39)

Since it did not crack and the sungod law says that all such will crack, therefore it does not be.

 

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Welcome to the
Taunton University of
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(post #61647, reply #14 of 39)

Got it...


Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming....

                                                                   WOW!!!   What a Ride!

"Some days it's just not worth chewing through the restraints"

(post #61647, reply #15 of 39)

What are you two doing awake?


Don't you have jobs to go to?


SamT


Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it. Andy Engel


SamT
A Pragmatic Classical Liberal, aka Libertarian.

I'm always right!
Except when I'm not.

(post #61647, reply #16 of 39)

http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=44621.19

I've been a working all night

wqhat's your excuse?

 

 <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #61647, reply #18 of 39)

Saving the farm from the forces of mother nature...


About lost the barn and critters...



Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming....

                                                                   WOW!!!   What a Ride!

"Some days it's just not worth chewing through the restraints"

(post #61647, reply #24 of 39)

Let me say again ALL --- in South Los Angeles WITH Expansive soil (Clayey), 3 1/2" slab. 


 

(post #61647, reply #30 of 39)

Yup, OK, But not all houses are built in south Calif. There really ARE other places in the country.

;)

Now we know why you said it though.

 

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Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
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Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #61647, reply #8 of 39)

A mono pour is when two pieces of an assembly are pour together.


Piffins slab with footing, for instance, you may also see this in basements, although I don't like it because the loading on a basment footing is much higher than on the floor.


A stem wall carries the mudsill. The 6" tall concrete wall under the framing in the garage is a stem wall. So are most basement and crawlspace walls. Like Jim's inverted T.


You could have a T footing, poured in two pours,  then pour a slab and 6' stem wall as a mono pour.


I would not try to pour footings and stem walls as a mono pour.


SamT


Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it. Andy Engel


SamT
A Pragmatic Classical Liberal, aka Libertarian.

I'm always right!
Except when I'm not.

(post #61647, reply #9 of 39)

"I would not try to pour footings and stem walls as a mono pour"


That's the only way I've done it or seen it done. You form up the footing and then set the stemwall forms on top of that. The steel goes into the whole thing at once, and then the concrete. No cold joint between the two pours and one visit from the concrete truck. A slab would be a separate pour, no real way around that.

(post #61647, reply #10 of 39)

David, you are right. I was thinking (or not) of the difficulty of mono pouring full height basement walls. Ow! I think I just bit my foot.


I've poured footing and shorter stem walls  monolithically myself.


SamT


Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it. Andy Engel


SamT
A Pragmatic Classical Liberal, aka Libertarian.

I'm always right!
Except when I'm not.

(post #61647, reply #17 of 39)

You form up the footing and then set the stemwall forms on top of that. The steel goes into the whole thing at once, and then the concrete. No cold joint between the two pours and one visit from the concrete truck.


Being self-taught in concrete forming and placing, and not having tried that, I'd like to expand.  Generally my walls are 15' high but I have something much shorter coming up.  One truck would easily do footing and wall. 


Can you add a little about slump, placement, and vibration?


PAHS Designer/Builder- Bury it!

PAHS works.  Bury it.

(post #61647, reply #19 of 39)

There's a short article coming out soon about monopours that deals with all those questions, Tom.  You might e mail Dan Morrison asking what issue it's scheduled for, but it might be the next one.


Pouring footing and stemwall together is a snap if the walls are short - 24" stemwalls are pretty standard here in the temperate Pacific Northwest.  I agree that pouring a slab, footings and stemwall monolithically is harder, but not that unusual. 


I'd say compaction issues and techniques vary with soil type.


 

(post #61647, reply #26 of 39)

In the 30'x40' shop building I am hoping to get the permits for "real soon now", a monolithic pour has been suggested by the steel building supplier as the preferred method.  I am also in the Northwest and have a 24" frost depth requirement. 


As explained to me (I have only worked on separate stem walls and slab) the base for a mono pour is prepared by compacting everything to beyond the area where the slab/stem walls will be poured.  The trench for the stem walls are then dug (with a mini-excavator in my case), the steel laid, and the thing poured. 


Not absolutely sure about the expansion joints and control cracks yet, however, but that is not necessarily related to mono vs two pours.  I guess I need to post my own thread to get some suggestions on how many expansion joints and control cracks I need for a 30'x40' slab.   

(post #61647, reply #27 of 39)

Is that glacial till you'll be building on down there, Casey?  Or is is sediment from glacial runoff?

 

(post #61647, reply #34 of 39)

Jim -


It's the muck that the Missoula flood of 10,000 years ago left when it swept most of Eastern Washington down the Columbia Gorge and into Oregon's Willamette valley... 

(post #61647, reply #36 of 39)

I don't know how that soil compacts, how stable it is, Casey, but up here on the glacial till I'd break that slab into 15x20' sections, at least.  Maybe 15x13'4", kind of depends on layout.


I'd have 6" welded wire mesh throughout a 4" slabb with #4 bar dropped in wherever a vehicle might park and a thinckened edge where the drive in door is.


You'd be far better off getting local advice though.  The longer I carpenter, the more I believe that site specifics play a MAJOR roll in design - everything from soils to appropriate roofing materials, and everything in between.


 

(post #61647, reply #20 of 39)

I'm talking west coast, mostly CA but a lot of the same up here in CA... example would be a crawl space foundation using a 16W x 12H footer with 8W x 12H stemwall on top of that. Form the footer or pour directly into a trench if the soil is adequate for precise excavation. In CA we would just 'cut' the footing form out of the clay soil and then form only the stemwall, probably using a form tie system like Simpson WTs.


With the much taller walls you're talking about, it would probably be two pours. The form work would be a lot heavier than for a simple crawl space.


I usually pour with a boom because that's the local pump and it's about $275 for a pour. He's the brother of the readymix guy and I tell them to make it just loose enough to get thru. Maybe it's a 3-4" slump? Then we rod it into the forms and vibrate it with a pencil.


All this form stuff is local and even individual practice. It would never have occurred to me to pour a footer first until I read about it in a FHB concrete book.


Edited 6/23/2004 10:14 am ET by davidmeiland

(post #61647, reply #21 of 39)

RL,


Out in these parts (SE WI) monolithic slabs are the norm for detached garages, and stem walls (when necessary) are typically laid up later with concrete block after the slab has sat at least a few days.


I've never seen the cracking problem that sungod has, but maybe because he's demo-ing the bad ones.  I have seen cracked slabs in the floors of those done the traditional way.  Though the times I've seen that, it's been in large, cheaper, tract built type stuff, where that type was required because the garage was attached.


Jon

(post #61647, reply #22 of 39)

My last few additions were off-grade, framed and I used the inverted T, combo footing and stem wall.

Usually, the footings are 16" wide but sometimes the engineer slips in a 20" wide. We only need 12" below grade (original undisturbed soil).

I drive paired 2x4's about 4' apart to define the width of the trench and use the transit to set the depth of the 2x4 to the height of the top of the footing. Then I excavate between the stakes and set the footing steel. I then build the stem wall forms, using a 2x6 on the flat for the bottom stiffener which is then screwed - one screw - to the top of each stake. I set the inner wall first then add the vertical steel, tied to the footing steel. I screw a reinforced plywood box at access and vent holes positions so that I have all the penetrations.

Then I place the snap ties if I need them, tie in a single continuous #5 at the top of the form and to the verticals and then attach the outer forms. A little tie wire through the sides of the form holds the #5 centered in the 8" form space. The 2x6's attached to the stakes hold the stem wall form in the exact position over the footing trench, the snap ties and plywood boxes hold the middle of the form and a perimeter 2x2 around the top of the form with 1x2 spreaders across the top hold the top of the form. The only external bracing back to the ground I've ever needed was to push the top of the forms to the string line. Don't forget to tie the forms together at the corners or you will have a blowout.

This works well in FL since the grades don't fall off drastically. This past pour needed a little extra digging on the upper half of the footing and a little extra footing side wall forming at the low end. Forms pop off easily and then the footings stakes are pulled and you're done.

(post #61647, reply #23 of 39)

Thanks guys. 


I've poured 400+ yds into my plywood&snap tie forms, with them sitting on a previously poured footer, sometimes 8' wide.  Was running a cabinet shop when I started this place.  At that time there was almost nobody around here pouring walls, everything was block.  In frustration I bought a how-to form book and jumped in.  4" slump is normal for me, but the readymix guys still can't believe I bother.  I figure the engineer spec'd it for a reason.  What I know is what I've read, and then tried.  Actually had a concrete salesman tell me that it was OK to water the hell out of the concrete, didn't decrease the strength.  About that time I quit listening to him.  Same guy told me to never, ever vibrate, as it would break the snap ties.  Yeah, right.  Only problem I've had was the vibrator died during one pour.  Now there's a spare on site.


My monolithic interest was for a 4' tall wall, L shaped with backfill.  My concern was to be able to fill the wall and vibrate adequately while still keeping it filled.  This'll be out of a chute.  Really just the issue of keeping the mud in the wall.  Or isn't it an issue?  Had trouble pouring retaining walls that formed a 45° top line.  Believe me, I wasn't trying to move mud with the vibrator. 


I haven't liked any pumping (boom) I've ever done.  Expensive, $700 per and up, and resulted in an inferior product.  To the point that I bought a crane just to lift a concrete bucket.  Unsure what I'll do with the crane after the next house is finished, but it was cheaper than pumping. 


PAHS Designer/Builder- Bury it!

PAHS works.  Bury it.

(post #61647, reply #25 of 39)

"My monolithic interest was for a 4' tall wall, L shaped with backfill.  My concern was to be able to fill the wall and vibrate adequately while still keeping it filled.  This'll be out of a chute.  Really just the issue of keeping the mud in the wall.  Or isn't it an issue?" 


What type plywood forms you use, Tom?  1+1/8" 2x8 panels with spreader cleats and snap ties?  3/4" AB formply with spreader cleats, snap ties and whalers maybe?  Hell, I've even used 5/8" with snap ties and double whalers to pour 48" tall stemwalls and then used the forms to sheath the roof...love those old ways.


Anyway, I wouldn't hesitate to form and pour a 48" wall and 8" footing mono.  Piece of cake.  Pour it right out of the chute if I could.  Keep your mud stiff, 4" slump would be fine, drier better (add plasticiser if you need better flow).  I'd pour about 6, or 8 inches above the top of the footing with the first lift so it has a little time to set up before filling the wall.  Then I'd go back and pour the wall in two successive lifts, vibrating the lifts together (and as you know, to eliminate those unsightly air and rock pockets.  LOVE that vibrator, man.)


Resist the temptation to button up the top of the footing in the name of keeping mud from flowing out of that opening.  The same hydraulic action that will lift mud over the edge of the footing can lift a buttoned up form right up out of the ground, stakes and all.  Been there.  Done that. Instead, keep an eyeball on that joint, and when mud starts oozing out over the footing form, you know to move to another pour spot until it sets up a bit and can handle more weight.


Whale the crap out of the bottom of your wall forms, and over brace the footings and any outside corners, that's where the pressure is; that's where they blow.  Hate to admit how many times I've seen forms blow, some on my watch.


Oh yeah.  One of the downsides to monopours is that they ARE messier.  I do my best to hose down the outside of the forms as soon as possible after pouring - do that on most pours, but it's a pretty high priority on a monopour.