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First off – I’ve read some of the other threads on cold weather concrete and from them I know at least some of you out there have experienced the problem of frost-heaved footings.
Here’s the scenario: Poured footings end of October – walls delayed. 2″ of foam, 300 straw bales and 6 weeks of temperatures between zero and 25 and guess what…The footings that were within 1/8″ of level all around are now within 1″ of level all around.
Obviously I’m not going to pour on these footings right now – my question is has anyone ever had this experience and if so what did you do? My first thought is wait until the ground thaws in April and hope they take care of themselves – how likely is this? If they don’t then what? I don’t relish the thought of removing 32 yards of reinforced concrete with a jackhammer.
Any shared wisdom – beyond using me as the poster child for why you don’t pour footings right before winter – is welcome!
Thanks in advance.
Replies
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Scott, I find it hard to believe that you couldn't prevent frost heave with 300 bales of hay. Obviously you did something wrong. Did you fluff the straw, or leave it baled?
I protected mine last year with 1/2 foam, and ten bales of hay. I am in sugar sand. Maybe that is the difference.
Anyways, everything will settle down after the thaw. I've seen many a pad heave, but none that stayed proud.
blue
*are these footings ? or foundation walls?if they're footingsand there is no frost UNDER them, then you can pour your walls on them...you don't really care if they're level.. it's the waqlls you're going to set on them that have to have a level TOP...if they're not footings .. but walls..then you have to determine if they are done settling after ( and IF ) they heaved..how do you know if they heaved... or if they settled?if there was some disturbed earth under the footings.. they may have settled and they may be in their final state .. if they heaved... you can hope they'll settle .. then pour..or you can grout under the heaved part .. then pour..we're talking about a house .. not a pad for a 4 lane bridge.. b but hey, whadda i no ?
*b WBA At Your ServiceGotta agree with gentlemen above. Wait until complete thaw and then pour your walls. Can't believe that all that prep didn't work. Is the soil around the footers obviously frozen ? Was any polyethylene used with the straw and foam ?blue....sugar sand ???
*I am more concerned about the freeze on green concrete than I am of the insignificant settling of the foootings. I am also concerned about the soil bellow and around these footings... but I suspect you don't really have a problem. Just pour your walls level in the spring.fv
*I think the point has been missed...things have moved 7/8 of an inch at least....I would wait till spring and possibly be prepared for some kind of fix...I would definitely fully rebar the walls both horizontally and vertically. Reinforced walls will easily bridge any soft areas created by frost under your footers...I think rebar would cost way less than any other solution too.near the stream almost gauranteeing my advice,aj
*I'm sort of curious about the missed point. I guess I take it for granted that stem walls should be fully rebarred. It is obvious that you'll have to do some serious checking Scott, climatic variations in this country makes it hard to come up with guarrantied info and results. Let me put it this way, I'm hoping you don't really have a problem, but I am nonetheless concerned as to why your footings settled an inch.fv
*i frost-heaved footings. not i footings settled And residential foundations generally are without rebar or very little at least in Upstate New York. And they hold up just dandy and are considered correctly built unless special circumstances such as soft areas are possible under the footings...near the stream still, but off to ski finally,aj
*Gentlemen,Thank you for all the prompt replies. I would have gotten your questions answered sooner but we were out all day finishing up setting the wall forms - ICF's.Let me see if I recall all of the questions.1) Didn't break the bales - knew it was better but also new we would be moving them hither and yon while erecting wall forms. We initially put 4x8 sheets of 2" foam perpendicular to the footings and completely covered them with an-split bales. Then we covered the whole works with reinforced ploy held down with pallets. To start setting wall forms we took up all that stuff, nailed down our channel and then split the foam lengthwise. 2' on the outside, 2" inside, 12" taped to the top of the row we stopped I I at the end of the day. Again with an-split bales completely covering foam and then some and with ploy again. It sat this way essentially undisturbed at the base as we continued stacking walls. As the weather has not allowed concrete delivery (we are 30 minutes from the plant) we decided to take this break in the weather today to finish setting and then pour Monday. As a final check on the footings I brought the laser back out and shot them - that's when I discovered that the least protected corner (round of all things) had lifted 1" relative to the other footings. It is on the downhill side of the excavation (9' of fall across the site from back right to front left.)2) The concrete shouldn't have been too green when (if) it ever saw freezing hemps. Poured them Oct. 21. 12x24 with 4 #4 bars all around. All formed. Some as deep as 6" in the ground, some only an inch (after basement excavation mind you - so all should be virgin soil).3) Soil is clay - not much of the smelly, slimy gray stuff (3% maybe) - mostly the run of the mill clay we see here in our part of Wisconsin. The clay didn't concern me to build on as I was a) on virgin soil I) installed perimeter drains inside and out and I) planned to back fill with gravel immediately adjacent to the walls.4) Wall forms are Ices (AMVIC) for the curious. As a side note I am very impressed with this product. My other experience was with Formtech which allows for very flexible foundations - we had a combination of 12" and 8" walls meeting at corners when we used them - but seem slightly under designed. We had one blowout - not at a corner - a tie simply let go. We scabbed on the plywood and kickers and kept going. We slowed things down and it held - but heard an occasional popping noise - made for an anxious couple of hours. Those walls were up to 12' high in spots and 12" thick.5) The walls are being reinforced anyway - #4 bar 16 cc horizontal and 12" cc verticals.Any more thoughts?Thanks for all the reponses - hope you all feel as Blue does that they will come back down - I'd sleep better the rest of the winter!Scott
*b WBA At Your ServiceI have a thought. You need to break open the bales and spread the straw like a blanket. Do it before things get worse.
*Scott - Are you sure you didn't just hydrate your clay and cause it to expand?Click here for more on bentonite clay in Wisconsin.Jeff
*I've learned two things since my last post - which is basically unintelligible...First, never use the spell checker.Second, our temps have actually been between -12 and 20 with many hovering around the zero mark.Tim, I think your suggestion is a good one. I'll be doing that shortly. The weather is supposed to be above freezing during the day for the next few days so I'll wait until some of the snow melts and then break the bales and cover with poly again.What surprised me about the footings lifting is that we have had something like 36" of snow (which is still on the ground) since December 1st. I thought that would have added enough insulation to make the difference.Also when we shoveled through the snow and unbaled the footings on Saturday to check level the top surface of the ground on the inside of the footing was not frozen - In fact it was actually mud in some places.The only way I can explain this is that we didn't cover out far enough and the frost came in from the sides. After setting wall forms we had 2 feet of 2 inch foam horizontally out from each side of the wall with bales of straw on top with the long side set perpendicular to the wall. Is it possible (read realistically likely) for frost in the vicintity of the footing but not directly below to move the footing?I'm starting to question the laser now. This was a quality laser, a Pro Shot L4, and we set it up at two different locations and the results were the same. I may triple check on Saturday with another laser, transit, or an antifreeze level.For those who are curious I'll keep you posted.
*Jeff,I really, really, really hope your wrong but boy does that sound plausible...Your link to info on clay hit me like a brick - We are 3 miles north of the Lafayette county line in Southern Wisconsin.It would explain a lot. Especially when I add that the excavation was very wet when dug even though weather had been dry for many weeks before the dig.You have me thinking that one of the previous posts about settling in stead of heaving could also be on the mark. The batter boards are still set but of course they've probably moved as well. Our benchmark is 300 feet away and I wasn't worried about hitting the relative elevation to an eybrow so I don't think I'll be using it to reference up or down an inch. It could very well be that these things are going up some places and down others.If your thought turns out to be correct I'm starting to see dollar signs. Can't leave expansive clay under a footing so what then? AB Chance drilled anchors, undermine the footing and filll with gravel.I feel like I'm walking off a plank here - somebody call me back....
*Scott, don't you just hate that feeling like your head is blowing up like a huge balloon. And the room starts to spin , feel weak in the knees and your gonna show the floor your last chow? AAAAAAh we live for these moments in construction. Just like final exam day, for the class you blew off all semester, but need to graduate. If it's expansive clay, call the trackhoe back, and get the footers out of there, excavate clay and backfill and tamp gravel in small lifts(8")It may cost now, but it will make you feel much better later when you don't have to walk around waiting for the first crack or worse. Keith C
*Expansive clays or frost heaves could explain the problem. It has certainly been cold enough ("between -12 and 20") and long enough (2.5 months) to freeze water in the clay and get frost heaves. Insulation (in the form of hay bales and snow) will slow, but not avoid the freezing of the footings and the underlaying soil since no heat was added after the initial curing of the concrete. For frost heaves to occur, you must have fine-grained soils (you do), temperatures below freezing (yep), and water ("the excavation was very wet when dug"). Spend about $10 on an 18" drill bit and $7 on a thermometer and find out what the temperature is down in the clay (let it equilibrate for 30 minutes after adding heat by drilling). If it is somehow still above freezing, than maybe it is expasive clays doing their thing. But I suspect there is frozen clay under the high spots.To NOT have frost heaves, you must eliminate at least one of those three conditions. You could overexcavate and backfill with NFS (non-frost suseptible) clean gravel fill. Or get and keep that part of the building heated. I wouldn't attempt to keep the clay dry - too dicey, too many ways to fail. But if you don't remove the clay nor keep it heated in following winters, the same problem can arise (so to speak) AND GET WORSE. Without going into the mechanisms of frost jacking, suffice it to say that in some conditions, frost heaves lift objects (like foundations and 40-foot deep pilings) out of the ground by a few to many inches a year. I have had wells get jacked up 3 to 4 feet in a decade. You're concerned about an inch now. I'd be concerned about several inches in the future. Sorry, I see a backhoe in your future. Or how about a heated basement? -David
*Scott, you should have fluffed the bales. If you didn't want to be the fluffer, you could have hired a fluffer...I know there's many around.I think you've indicated that only one corner has raised up, the round corner of course. I wouldn't be in too much of a hurry to pour that section, but you always could grout it later if the expected gap occurs.I also don't think I'd be too interested in digging out all the clay. You might end up in China.blue
*Scott you have to relax a bit. Mike and Francis are right. Wait until spring then check your footings. They will probably be out of level even more by then with a few cracks added for good measure. This isn't a big deal. Pour your walls,backfill properly,and you won't have any problems.Two things you need to realize. The footings may have heaved because the soil under them froze (wet clay!). All the hay in the world would not have prevented the ground around the footings from freezing, so you didn't do anything wrong. The hay and poly technique only works in helping freshly poured concrete retain the heat produced during the curing process. If there is no heat then there is nothing to retain. If you put an ice cube in a cold thermos outside in zero degree weather it will stay frozen! So forget about breaking open the hay bales or adding more hay. If the ground is frozen it will stay that way until the weather warms up.Second, don't worry about the level of the footing. It's irrelavant once you pour your wall. Think of it this way. Imagine the wall and footing as being one solid entity. Now imagine a split line near the top of the footing portion at a slight angle to the top of the wall portion. Does this affect structural integrity? NO.Scott, as long as there is nothing wrong with the ground itself you should be fine. The clay soil most probably froze producing the results you noticed. This is normal since you didn't have sufficient backfill to prevent the frost from reaching the ground below the footings. Once you have enough backfill over your footings the problem will not get worse as some have suggested.You'll be fine Scott. Don't sweat it!CC
*Hello again,Thanks for all of the valuable input guys! The suggestions and reassurance are both welcome. I love the thermometer idea - I'm going to go buy one of those indoor outdoor jobbies with the remote sensor tomorrow and give it a try.Being an electrical engineer - although I hesitate to bring that up given all the discussion lately about engineers - I'm starting to feel like a lawyer ;) I'm going to hire a soil testing firm to tell me what I'm building on. Luckily the company I work for has a firm we use and are happy with so I'll be looking to them for further input.I do appreciate all the thoughts - although I did think the top of my head was going to come off earlier today while thinking about nightmare scenarios!The fact that I don't have frozen soil at the surface below the bales is what concerns me the most. If it were frozen there I'd be convinced of frost.The thermometer (and what it takes to get the hole drilled to get it in the ground) may say a lot. I know the soils engineer will SAY alot!Anyway - I'll hope for best - and try to wait patiently until Spring arrives.Thanks again everyone!
*Scott,After the soil test is done, if they find no evidence as to why it heaved, what about the earlier thought concerning the laser level? Lets see..... you got 1 inch too high on one corner of your forms, and all the other corners and whatnot are "right-on." Could 'nt it be possible that a simple elevation mistake was made by someone? Perhaps this corner elevation grade was set 1 inch too high all along?Not trying to point fingers, but rather to put your mind at rest. If this was the case, your problem is solved. Build the wall to make up the 1 inch difference accordingly.Davo.
*Scott - I certainly hope I'm wrong too. I suggest you contact a local soils engineer - it probably wouldn't cost too much and since this is a relatively common subsoil problem in certain areas, particularly yours, he/she might be able to visually confirm bentonite. If not, a sample can be sent to a lab for analysis for a minimal amount.The posts about the footings being OK out of level are right - but they have to remain stable over time, obviously.Jeff
*Update for the interested:I buried an outdoor thermometer probe about 16" down on the inside of the footing at the point where it appears to have lifted 7/8". After about 30 minutes it had dropped to 31.1 degrees and stabilized. So I'm thinking frost is the culprit.As a safety measure I'm meeting with a soils engineer this coming week to look it over and take a sample for analysis. We'll see what it tells us.Scott Lind
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First off - I've read some of the other threads on cold weather concrete and from them I know at least some of you out there have experienced the problem of frost-heaved footings.
Here's the scenario: Poured footings end of October - walls delayed. 2" of foam, 300 straw bales and 6 weeks of temperatures between zero and 25 and guess what...The footings that were within 1/8" of level all around are now within 1" of level all around.
Obviously I'm not going to pour on these footings right now - my question is has anyone ever had this experience and if so what did you do? My first thought is wait until the ground thaws in April and hope they take care of themselves - how likely is this? If they don't then what? I don't relish the thought of removing 32 yards of reinforced concrete with a jackhammer.
Any shared wisdom - beyond using me as the poster child for why you don't pour footings right before winter - is welcome!
Thanks in advance.