Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?

 
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Old 11-30-2009, 07:51 PM   #1
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Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


New Question: (12-11-2009) See Post # 7


I plan on pouring a slab foundation for an 8x12' shed I'll be erecting soon. The ground in the area we intend to put the shed appears well drained. The HO is really concerned about frost heave - although he admits to never having had any frost heave problems before; nevertheless, this is Kentucky & we do get freezing weather...

My plan was to dig about 7 inches down, back fill with gravel compacted to 4 inches & pour a slab 4 inches thick (thicker at the edges). I figured frost heave likely wasn't a problem, given the size of the slab & condition of the ground - but wanted to ask before I got started anyway...

Am I right thinking that frost heave isn't a concern for this structure? if not, would using concrete tubes & pouring 24" footers at the corners & at about 6' down along the edges of the length be sufficient?

(While I've helped pour sidewalks, etc. - this is my first foundation as the contractor where I've got to do the planning as well as the execution!)
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Old 11-30-2009, 08:26 PM   #2
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


If this is to be a free standing structure, (not attached to any other building), I would not be too concerned about frost heave.

If frost does affect this, it would most likely affect the entire concrete pad, lift it uniformly and return it to its original location uniformly.

If you want to add some strength to this, a "turn down" edge at the perimeter with a couple pieces of rebar will do a lot with little cost.

That being said, I don't know the weather extremes there in KY. We will soon be doing a storage building with a monolithic slab/footing, 16 X 32 building that will have footings to below frost line. Better safe than sorry.

If the client has concerns and is willing to pay to have the footing, I would do a frost depth foundation.

If you talk him out of the foundation and there are problems later.....you will get the blame.

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Old 11-30-2009, 09:39 PM   #3
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


Frost heaves are a concern in my area, we have to put our footings at least 48" below grade.

However, plenty of garages and sheds are built on floating slabs without problems. 12" thick around the perimeter, 8" wide on the bottom and taper to 4" thick slab. 2 continuous rebars around the perimeter with mesh embedded in the whole thing.

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Old 11-30-2009, 09:46 PM   #4
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


Here in MI we can do free standing up to 400sqft monolithic with turn down minimum 12" below grade just like David C posted
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Old 11-30-2009, 10:30 PM   #5
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


Yeah what they said
I wouldn't worry about it much. not for a free standing shed that size. It may lift but will settle back down again without a problem I can see.
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Old 12-03-2009, 11:34 AM   #6
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


It would be better not to pour your corners below the frost line while having the mid span footing above the frost line. This could cause differential frost heaving.
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Old 12-11-2009, 09:25 AM   #7
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


Thanks folks!

Another question: since this is my first foundation I'm not really up to speed on what type of concrete to ask for. Since temps are ranging from upper 20's to lower 40's, do I need to request anti-freeze in the mix?

@ CORN: I planned on 6 footings; one at each of the four corners & one at each edge midway down the long axis. Would that be sufficient?
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Old 12-11-2009, 09:41 AM   #8
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


I'd want either continuous footings,
or no footing, just turn down the edge.
Ask the ready mix guy for calcium
and full air.
He knows what to do.
They don't use antifreeze,
it's hot water and accelerator.
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Old 12-11-2009, 10:01 AM   #9
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


And some blankets.
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Old 12-11-2009, 10:23 AM   #10
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


I agree with the two posts above. It's important the concrete not fall below 50 degrees for the first 5-7 days.
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Old 12-11-2009, 12:46 PM   #11
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


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Originally Posted by WarnerConstInc. View Post
And some blankets.

Blankets? Like packing blankets? Or are you talking about some specialty electric blanket I'd have to rent?

Whoops... forgot to Google before I asked: This article suggests I can use packing blankets & plastic tarps. --Thanks for the tip!

Next Q: When we poured the sidewalks & steps, we had the HO water the crete for several days. Doesn't seem like a good idea here. Does spraying on a liquid curing compound (as suggested in this article eliminate the need to keep the surface wet?

Also, what's the best (low-cost) method for heating the ground / gravel before the pour? Propane heaters like this one?
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Old 01-06-2010, 10:47 AM   #12
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


Yes to your last question, although you're probably done by now....The morning after our slabs, we apply UGL masonry sealer, in water base....It is dynamite as a curing agent, since I don't usually have the time to maintain a damp cure....2 thumbs way up...
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Old 01-11-2010, 12:41 PM   #13
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


Quote:
Originally Posted by Panzer5 View Post
Thanks folks!

Another question: since this is my first foundation I'm not really up to speed on what type of concrete to ask for. Since temps are ranging from upper 20's to lower 40's, do I need to request anti-freeze in the mix?

@ CORN: I planned on 6 footings; one at each of the four corners & one at each edge midway down the long axis. Would that be sufficient?
A good mix would be a 6 and one half sac mix with 6 to 8 percent air,blend sone, 50% no8 and 50%no57 lime stone, noncloride or calcium about one percent unless u can work fast then two percent, use blankets after pour or visqueen with straw.
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Old 01-11-2010, 12:54 PM   #14
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


Quote:
Originally Posted by Rockmonster View Post
Yes to your last question, although you're probably done by now....The morning after our slabs, we apply UGL masonry sealer, in water base....It is dynamite as a curing agent, since I don't usually have the time to maintain a damp cure....2 thumbs way up...
U should not seal till 28 days after cure, apply a cureing compound then seal at later date, that is a mistake alot of contrators not cement men make, read aci specifications.
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Old 01-11-2010, 12:59 PM   #15
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Re: Pouring An 8x12 Concrete Slab Foundation For Shed - Frost Heave A Concern?


Quote:
Originally Posted by Panzer5 View Post
New Question: (12-11-2009) See Post # 7


I plan on pouring a slab foundation for an 8x12' shed I'll be erecting soon. The ground in the area we intend to put the shed appears well drained. The HO is really concerned about frost heave - although he admits to never having had any frost heave problems before; nevertheless, this is Kentucky & we do get freezing weather...

My plan was to dig about 7 inches down, back fill with gravel compacted to 4 inches & pour a slab 4 inches thick (thicker at the edges). I figured frost heave likely wasn't a problem, given the size of the slab & condition of the ground - but wanted to ask before I got started anyway...

Am I right thinking that frost heave isn't a concern for this structure? if not, would using concrete tubes & pouring 24" footers at the corners & at about 6' down along the edges of the length be sufficient?

(While I've helped pour sidewalks, etc. - this is my first foundation as the contractor where I've got to do the planning as well as the execution!)
Make sure the base is sound and compacted, use a 57 lime stone it costs more but is one of the best.

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