We recently purchased a 40 year old cottage.
I guess we didn’t check things very well, as we discovered the footer portion of the slab has heaved significantly around the entire building. I suspect this problem occurred way back when we had those very severe winters of extremely low temps
It’s confusing, because the walls all seem plumb and there’s no apparent damage to the structure. We really noticed the problem (and determined a possible cause) when we added to our building. When we dug the new footer (to code), we discovered the original foundation/footer was only down two courses and on gravel!
We’re not too concerned about the condition, but it does present a problem now because we’d like to put new flooring throughout the old building. Every time we pick a flooring type, we end up getting stuck on how to handle the change in levels as we approach an outside wall. We’ve considered the new Pergo-type flooring, sheet vinyl and vinyl tiles. We’re stuck.
Is there any way to bring the floor up to the level of the footer/foundation. short of repouring everything? .
Replies
I doubt that frost heaves caused the problem. Frost might have pushed the building up but it would also let it down in the spring. I would nominate contraction of the soil under the body of the slab as the soil dried out. Of course this is all just a guess.
Just how bad is this problem and how does it affect the present floor?
That's what I thought; up in winter, back down in spring. We're located in NW PA.
I estimate (I should measure) there's somewhere between 1/2 and 1" of drop. I did remove a section of the bottom plate to install a door between the old and new buildings. I had to fill cores of the block I exposed! As I said in my initial posting, we're not overly concerned about the integrity of the building. We've owned it for three winters and would like to redo the old floors.
I don't know concrete construction, but it looks as though they may have poured the slab 'inside' the block foundation. I thought they would have used two or more courses of wider block (12"), topped with a course of 8" to form a footer for the slab?
Consider mud-jacking to bring the settled part of the floor up.It is possible that for a cottage, with your soil type, you don't actually need a footer, especially with the gravel down there (if thick enough.)But you do want to protect against frost heave and excessive changes in moisture levels in the soil, perhaps by re-landscaping and adding foam sheets just off level around the perimeter.Whatever you do, you need help with expert knowledge of your area.
Fighting Ignorance since 1967
It's taking way longer than we thought
Wow!
Mud-jacking sounds serious, risky AND expensive. Could you explain how it's supposed to work?
>>Mud-jacking sounds serious, risky AND expensive. Could you explain how it's supposed to work?Not really, at leat 1 & 2They'd drill some holes through the slab and then punp a (in my area concrete/lime (I think) slurry under the slab which floats it back up (close to level) - it wouldn't be done under the foundation, just under the slab.Cost? Well, in my area, it's about $150 for the first section of sidewalk slab, but a chunmk of that is to get 'em out and set up.Most construction in my area is crawl or basement, but I've seen it done on some slab built houses around here.
Fighting Ignorance since 1967
It's taking way longer than we thought
Thanks again to everyone.
I don't think I have a 'footer', in the traditional style. As I mentioned earlier, all we found was two courses of block sitting on a gravel base? Maybe I should be talking to some contractors in this area? I understand about just jacking the slab, but would be nervous about fracturing, especially along the block perimeter?
If the slab has subsided in the middle (or risen at the edges) then it's already fractured. Mud jacking may make the cracks more obvious (they're getting squeezed closed right now, except right in the center), but shouldn't cause substantial additional cracking. But like I said earlier, there is some risk of damage to under-slab plumbing, depending on where it is in relation to the work that would need to be done.Another option would be to just use a floor leveler over the whole thing. You wouldn't want to use an expensive leveling compound for it all, but could probably use something cheap for the bulk and then a thin layer of the fancy stuff on top. Of course, this would "bury" interior wall plates unless you first shimmed them up -- an option worth considering.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
FWIW, Wright used gravel "footers" in some of his projects, and, as some have said, railroads use gravel to maintain level tracks with great weight being moved over them.The "gravel footer" idea is novel, however, and you're unlikely to find a contractor who is willing to stick his neck out and work on/evaluate one.
Fighting Ignorance since 1967
It's taking way longer than we thought
Yeah, they use gravel footers under treated wood foundations.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Ahh, I forgot.What are typical specs for that use?
Fighting Ignorance since 1967
It's taking way longer than we thought
But this is not a treated wood foundation. There is a world of difference between a 2x8 spreading loads and individual CMUs with voids sinking into gravel in a high water table. Somebody saved a coup0le thousand on the footers and the house will suffer forever because of it.
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WOW!
You guys are really into this, but, remember it's not the footer that sank. Either the footer heaved or the floor sank. Which is more likely here in NW PA.
you don't have a footer so it could not heave.
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We don't know how deep the gravel is (that I recall) or what type of gravel it is. In theory, full-fractured gravel of the right size will work as a foundation and footer. This might actually be a preferred arrangement in this potentially marshy area.Of course, if it's just six inches or a foot of common driveway gravel then that's a different matter.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
i'm sorry, that was too short.You have one of the most unique, poorly built foundations I have ever heard of, placed in wet clay soils that probably prevented them from digging deep enough to get below frost level. honestly, it sounds like they did everything wrong that they could, so it is really hard to diagnose from here.But if I have to make educated guesses or assumptions, it would be that they also did a poor job of infilling and did not properly compact the fil materials and it thus settled later, letting the center sink. Also, it doesn't have to be an either/or choice. With such a shallow perimeter foundation, it could be both.
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That makes more sense than anything I could have thought to be the cause. It wasn't that the perimeter wall heaved, but the floor (over time) sunk because the builder was unable to properly compact the soil.
I think I'll try looking at this problem from the other side. Since it appears bringing the floor back up to level with the perimeter (instead of footer) would be costly and not without some risk, I'm going to explore other options. We actually thought about the following, and then went into hysterics laughing about it:
1. Measure the amount of fall between the perimeter and the floor at several locations around the edges. 2. Then determine if the interior walls are at floor level or perimeter level. 3. Install plywood (treated) across the entire floor surface to within 4 or 5 inches of the edges. 4. Use a filler compound to bridge the gap between plywood and raised edges. 5. Cover the whole thing with luan and floor covering (vinyl, laminate, carpet).
One solution I got from an acquaintance that was to burn the place down and rebuild, or just move away!
I agree with Pippin. We don't really know what caused this. There are likely a number of factors.
Since we don't know and since the building above seems fairly level, I wouldn't recommend an expensive fix. I would try simply leveling the floors by pouring another 2" of concrete, if this is practical, and don't put any expensive flooring in this part of the house. Good luck.
What is your climate/area?
From your description it sounds like you have two courses of concrete block directly on gravel/stone. Is this correct?
Then there is a slab poured over this?
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I just posted a reply to another member.
Climate area is NW PA. Soil is thin layer of top, sitting on several feet of clay and very close to water table, as we're less than a mile from big lake. I remember when we tapped in for the sewer, the tap was under 2' of water. Had a heck of a time pulling their cap off, so we could stick our pipe...
<<sitting on several feet of clay and very close to water table, as we're less than a mile from big lake.>>Now we're getting somewhere.
Well, I still hve no idea if you have a footre or not, but like catskinner said, we now have the key to the puzzle. you are sitting on clay, in water, in a freezzing climate.Water feezzes.
Clay expands when it holds water.The house sounds like it is floating on wet clay, so it comes and goes with the water
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You don't say where this is, or what the nominal frost depth is there.
I'd agree that it sounds more like the center has subsided. If you don't have much in the way of floor coverings down now, you might want to get the center mud-jacked, though there is a risk of damaging under-slab plumbing if this is done.
So far I think Schelling and Piffin have you headed the right direction.
All of the speculation about the merits of your gravel "footing" are somewhat beside the point. If the walls are in good shape, then the foundation (such as it is) is probably not the problem.
FWIW, an actual "footing" of stone is also called a rubble trench foundation. In the proper application it is entirely acceptable, and if properly constructed will function just fine. But that does not sound like the case here. <G>
But let's put that idea to bed for good. Either the walls are or are not moving. If they are not moving, good. If they are moving, they are either moving uniformly (unlikely) or not. If they are moving uniformly, that is, putting no shear stress on the structure, then you still have no problem there. If they are not moving uniformly, you either do or do not exceed the shear strength of the wall system. If you have not exceeded the shear strength of the wall (probably a deflection of somewhere between 1/600 and 1/1000 of the span) then you still have no problem. As you approach 1/500 to 1/250 of the span you might see some cracking, especially at the corners of windows and doors.
Doesn't sound like that is the case. From what you describe the problem is out in the middle.
Sounds to me like the challenge you are faced with is not complicated, but it is somewhat more complex than some of the posters here have indicated.
If you have any intention of keeping this place or selling it with a clear conscience, mud-jacking is out of the question, as is adding more concrete.
You likely have several failure modes going at once here. The obvious ones are as Piffin and Schelling pointed out. As clay gets wetter and drier it can change in volume. Some clays more, some clays less.
Oddly enough, not only can it change in volume, but at the same volume the bearing competence will change with the moisture content.
The slab you described is often termed "floating." Normally that is a figure of speech that means it is not tied into the stemwalls, rather resting independantly on a properly prepared subgrade. Unfortunately, in your case the interpretation may be somewhat more literal.
What is also likely is something called "shear failure." All soils have some degree of shear strength. Well-compacted and generally well-graded cohesive soils at 7 to 9 percent moisture content have a great deal of shear strength. Wet clay is sort of at the other end of the scale.
When you load saturated clay it tends to move.This is also sometimes called "creep." This is not really a settling process, but a lateral displacement. It is not at all unheard of for clay to displace around a foundation and move upward around the outside of the structure in reaction to the downward pressure of the weight of the house.
This is a very slow process, as much as 10 years to be noticeable. The bad news is that it does not stop until you remove the moisture.
Anything you do to add significantly more weight will make the problem worse. So no more concrete and no more grout.
So you see, your idea is really not ridiculous at all. You can level the floor as you described, use the flooring of your choice, and don't worry about it. At least for a few years. <G>
All in all, I think you are in a lot better shape that you thought. If that's as far as it's moved in 40 years, and if the walls are sound, I would not worry about it.
An inch or so of concrete (especially if lightweight) will not add significantly to the slab weight (unless the slab is woefully under-sized in the first place).I forget if it was said how old this structure is, but gather that it's 10 years at least maybe much more. Most compaction and drying that could occur has occurred. The major hazard is that if the ground becomes more saturated it could heave, elevating the center.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Thanks for the reinforcement. I tend to agree, as the building has been on this site quite a while and hasn't really moved that much. As you pointed out, everything on the slab has maintained plumb and square. I haven't removed any of the tile, but they don't show any signs of cracking, except along the edges. I just remembered why we didn't notice this condition prior to our buying it.
Every square inch of the floor was carpeted. I don't think it was a ploy by the seller, as the carpet was all old and worn. I really think it was more to a) Cover the unsightly edges and b) make it easier on the occupants as they were getting up in age (He was 83) and down in health.
As I'm writing this, I'm able to see a good portion of the back wall. It appears to approximately 1/4" to 1/2" difference. It also appears to be uniform along all edges.
I will take all the information gained in this discussion and go to work.
Good luck. Stop back by here and let us know how it turns out.
OK, It'll be a while. I'm still trying to finish the addition that uncovered all this mess. Things are going slowly, but steadily. Might save the old floor for next season? You guys have been a big help.