#11  
Old 04-09-2014, 05:24 PM
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Default Re: Concrete Foundation Base Cracked...Damn it!

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Originally Posted by stonecutter View Post
What???!! Why in the world would you want to pour another slab over another that may have a bad base? Answer...you don't. And further, an isolation membrane won't stop the new slab from cracking if he anchors it to the existing stand, and that keeps settling...if that's what's happening.
Why.
Pouring a new slab on top of the existing raises the floor out of the moisture
The new slab tied to the existing walls supports the oven ties it together and reduces the span of the base thus reducing the bending moments that induced the cracking in the old slab
Isolation of the new slab from the old slab prevents transfer of moisture and also prevents transfer cracking from the old slab

Nothing he can do will reduce movement due to frost but the suggested actions will result in the oven moving as a unit not breaking it's back
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  #12  
Old 04-09-2014, 06:50 PM
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Default Re: Concrete Foundation Base Cracked...Damn it!

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Originally Posted by Toomulla View Post
Why.
Pouring a new slab on top of the existing raises the floor out of the moisture
The new slab tied to the existing walls supports the oven ties it together and reduces the span of the base thus reducing the bending moments that induced the cracking in the old slab
Isolation of the new slab from the old slab prevents transfer of moisture and also prevents transfer cracking from the old slab

Nothing he can do will reduce movement due to frost but the suggested actions will result in the oven moving as a unit not breaking it's back
Here's why....

The existing slab might have a problem with settling or it is too thin and unreinforced ie; it is not adequate for a freeze thaw zone. I don't know if you have experience building in that type of climate, but problems will magnify with every cycle.

Pouring a slab on top of another and fixing it to perimeter walls does absolutely nothing to support the load applied above it. So, if the slab below continues to settle, the walls settle with it. Why? Because a row of slab pinning is not designed to support weight. You may not see a crack in the center of the new slab, after the new slab is poured, but if your base is bad, they will show up somewhere else....that is a fact.

The new slab reduces the span of the base?? How does that happen? The pour isn't under the footprint of the stand..it does nothing to support the load. And pins alone cannot support the base.

Thinking you are going to unify the structure with an over pour and pinning it, hoping it stops any settling is wishful thinking...it ain't gonna happen, because that's not how it works.

IF this is a settling problem, he will know it if the structural slab starts cracking. But unless this thing starts sinking into the ground or he sees some other major failure, then anything done now may not be the best course of action.
The only way I would agree with an over pour is after being sure there is no more settling or if the next freeze thaw cycle doesn't effect the oven. Then you have a nice new wood storage floor.
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Last edited by stonecutter; 04-10-2014 at 05:16 AM. Reason: Sp
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  #13  
Old 04-09-2014, 08:32 PM
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Default Re: Concrete Foundation Base Cracked...Damn it!

Read my reply I agree nothing will prevent it moving it's about getting some improvement short of demolition
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Old 04-09-2014, 08:34 PM
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Default Re: Concrete Foundation Base Cracked...Damn it!

I did read the reply, that suggestion is just going to add more material to remove later, if the existing slab is no good.
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Old 04-09-2014, 10:35 PM
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Default Re: Concrete Foundation Base Cracked...Damn it!

I agree he will have to decide to either try and mitigate the problem, can he live with the oven out of level , or decide to pull it down and build the footing on a solid foundation below the frost line
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Old 04-12-2014, 05:44 AM
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Default Re: Concrete Foundation Base Cracked...Damn it!

My thoughts are simple, put frost walls and footings in, at the beginning. There is not a solution for the cracked slab. Hope for the best, but you can not control the freeze, thaw cycles. How do you put foam under a cracked slab after it is poured? Are you rigging the whole oven and picking it up with a crane? As far as tying the slab to the walls with pins,I would tend to leave it alone as this could make the oven move with the slab.
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Old 04-12-2014, 08:09 AM
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Default Re: Concrete Foundation Base Cracked...Damn it!

Ummm.....my suggestion about the foam is to protect it from future damage. If he lays some 2" thick foam around the base next winter, weighs it down, it will NOT freeze again. It may not look nice (you can cover it up), but it will not freeze again. It's not going to do a thing about what's already done, but if he leaves it as is, the foam will work, if he keeps it in place. Always pay attention to the north facing side. It almost always freezes and heaves there first. Also get as much soil around the slab as you can.
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Old 04-12-2014, 08:32 AM
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Default Re: Concrete Foundation Base Cracked...Damn it!

Alot of people have the misconception that frost comes up from underneath a slab and does the damage. It doesn't. The ground under a slab is actually quite warm, even in colder weather. The damage comes from outside the slab, along the edges. It gets under an edge, expands and lifts up the slab and does it's damage. I've seen firsthand what frost can do, many times. That's why I have to chuckle a bit when I see people dig down under a slab (before pouring) and place sonotubes, etc., supposedly to prevent frost heaves. Waste of time and money and that can actually be quite detrimental in some cases. All he can do now is to somehow protect it from future damage by keeping the edges of the slab well covered, thus keeping the grounds' natural heat in and the cold out. I've done this quite a few times w/slabs. He also can actually dig down a few inches around the perimeter of the slab and bury the foam, keeping it tight against the slab edges. Then cover it w/soil.Works like a charm. Having said all this, what's done is done and all he or anyone can do is live w/it and take steps to stop future damage. Or.......tear it all down and start over.
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Old 04-13-2014, 06:22 AM
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Default Re: Concrete Foundation Base Cracked...Damn it!

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Originally Posted by NCMan View Post
Alot of people have the misconception that frost comes up from underneath a slab and does the damage. It doesn't. The ground under a slab is actually quite warm, even in colder weather. The damage comes from outside the slab, along the edges. It gets under an edge, expands and lifts up the slab and does it's damage. I've seen firsthand what frost can do, many times. That's why I have to chuckle a bit when I see people dig down under a slab (before pouring) and place sonotubes, etc., supposedly to prevent frost heaves. Waste of time and money and that can actually be quite detrimental in some cases. All he can do now is to somehow protect it from future damage by keeping the edges of the slab well covered, thus keeping the grounds' natural heat in and the cold out. I've done this quite a few times w/slabs. He also can actually dig down a few inches around the perimeter of the slab and bury the foam, keeping it tight against the slab edges. Then cover it w/soil.Works like a charm. Having said all this, what's done is done and all he or anyone can do is live w/it and take steps to stop future damage. Or.......tear it all down and start over.
That can help if the frost depth is shallow, but in New England I have seen frost reach down deeper than 24" and when it's that cold, the slab drops below freezing along with the ground below it...and foam board won't stop the ground from moving under the slab, especially so if there is a lot of water in the soil.

Bottom line, it doesn't hurt putting it in, but it won't completely protect the slab from frost.
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Old 04-13-2014, 08:39 AM
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Default Re: Concrete Foundation Base Cracked...Damn it!

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Originally Posted by stonecutter View Post
That can help if the frost depth is shallow, but in New England I have seen frost reach down deeper than 24" and when it's that cold, the slab drops below freezing along with the ground below it...and foam board won't stop the ground from moving under the slab, especially so if there is a lot of water in the soil.

Bottom line, it doesn't hurt putting it in, but it won't completely protect the slab from frost.
No, it won't completely stop it or protect it, but except in very extreme cases, it works just fine. I have taken out slabs before in the dead of winter, only to find the ground underneath completely normal, although the ground around it was frozen 14" down. We had to use jackhammers just to cut the ground so a backhoe could tear up chunks of ground, which we measured to be frozen 14" solid, yet under the slab was fine. I've seen and worked on lots and lots of "frost cases" in my days. Too many. And they could all have been avoided. And, as I said earlier, properly placing 2" foam around a perimeter of a slab will work in "most" cases. It is only offered as something to try that will probably work, as an alternative to ripping it all out. Nothing will ever take the place of doing it right. One of the best pieces of advice to offer to people planning to pour any slab, is if you have severe cold and/or moisture, have someone who really knows what they are doing help or advise. It's what holds up your whole oven and it's the most important. You only get one chance to do it the right way. Unless of course, you tear it all out, then you get another. Not a place to cut corners.
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