Pole Barn Slab Questions

[QRTRHRS]

I don't know that this would be redundant with the foam insulation or not. There is a bubble wrap type of insulation for use under slabs that has properties that allow for movement of concrete.

I can tell you that when I built my last barn, I personally rolled the ground with a 13 ton vibratory roller while my contractor did the bulldozing. When the builder did the center aisle slab (16x120'), he dug out 4" and put in 2b stone and tamped it. I forget now if it was 3000 or 5000 psi but it is 6" thick with wire, poured in sections then cut every 12' for relief. No insulation or heat. Danged if everyone of those slabs did not crack in the center (parallel with the length of the aisle). It is a horse barn but I had gone with 6" just in case I wanted to run through with heavier tractors and such.

 

[erict]

When I built my pole barn I did not need a rat wall(was not code) nor did I need a permit. Since I dont have a rat wall I installed 3' galv field fence around the whole outside of the pole barn to stop any digging of critters. So far so good. The slab looks the same as the day I had it installed. This is my workshop. Code has change since then.

 

[EddieWalker]

This is turnign into a very informative post! Reading all that goes into a slab up north compared to what we do down here is just amazing!!!

From personal experience and what I've read, I'd use rebar over wire mesh every time. Wire mesh will give you more strengh for allot less money if it's installed correctly, but it's just about impossilbe to install correctly. The wire mesh needs to be in the middle of the slab to function. The way to get it there is to pull it up by hand while pour the concrete. If you get half of it where it's supposed to be, your lucky. But there's no way to know where the bad spots are until it cracks.

Rebar can be held in position with chairs or blocks and will stay where you need it during the pour. For me, this is a huge benifit and enough of a reason to spend more for rebar.

Good luck,
Eddie

 

[gates]

Edddie,
You are 100% correct about the wire placement. Most people will not spend the money to put the wire up on chairs. They depend on picking it up as they go. The chairs make it a no-brainer and assure the wire is where it needs to be.
We use rebar only when there are design loads on the slab that are not obtainable with wire. We use wire mesh in multiple gauge sizes 90% of the time.

Ron

 

[PaulT]

So let me summarize what I think the consensus seems to be so far for a floating slab with radiant heat.

* Compacted soil/gravel
* Vertical insulation at the perimeter
* Horizontal insulation under the slab
* 6" thickness
* Wire mesh properly placed with chairs
* exterior aprons/walkways floating independently of interior slab - air entrained, poured at a later date from the interior slab
* 4000-5000 psi
* Fiber reinforced
* No need for a frost wall/footer in doorways
* No need for a vapor barrier if horizontal insulation is used

What I am still not sure of:
* Do I need a thicker edge, and is the purpose to strengthen the slab or to keep the frost out?
* If it is to keep the frost out, will it really do that if its only 18" thick around the perimeter, with a frost line at 42"?
* How thick should the exterior aprons and walkways be?
* if the barn is 28 ft deep, with 3 bays (12 ft wide, 16 ft wide, 12 ft wide), how should the slab be poured and separated (monolithic, monolithic then cut with a saw, poured in sections)

 

[gates]

Pault,
You do not need a thicker edge for concrete strength.
18" will not keep the frost out in a 42" frost line area.
5" is adequate if poured correctly and you have a good base.
The slab can be poured either continuos or individual pours.
It depends on your man power, you do not want it to get away from you.
Something that size can be easily poured continuos.
For the control joint placement in feet go 2 1/2 times the thickness of the slab in inches times 12. An example would be a 6" slab would have control joints at 15' on center. I do not exceed 20' spacing no matter the thickness. If you have an inside corner, ie. corner protruding into the slab, pick up a set of control joints off of the corner. If you saw cut the joints be very careful of the radiant tubing. The joints should be planed and considered when you install the tubing. Some tubing manufactures want sleeves on the tubing where it bridges a joint. Others just set the tubing deeper in the area of the joint. The floor should be cut as soon as you can walk on it, the sooner the better. If you own a soffcut saw, cut it as soon as you can send the saw accross it. If you pour the floor in sections you will need to put in a construction joint. This can be either a keyway or dowels. This will lock the slabs together and keep them in the same plane. Your concrete placement guys should know this info. If they do not get someone who does!

Ron

 

[PaulT]

Thanks Ron,

I was really looking for a no-nonsense response like yours to help me understand just what I needed to do to prep the pour and reduce total cost, assuming I would hire experienced guys to do the placement.

 

[gates]

Pault,
This is one part of the job, concrete work, that you truly get what you pay for. There is a lot more to concrete placement then meets the eye. All of the following come into play. Site conditions, concrete additives ie. plasticizers, admixes, water reducers, water content, air content, PSI, concrete temperature, air temperature, humidity and even if the wind is blowing at pour time. Concrete placement is definetly not rocket science but it does require experience. Remember this, you will look at that slab for a long time. It is the finished product. I would not start cutting corners now.

Ron

 

[rambler]

</font><font color="blue" class="small">(
* Do I need a thicker edge, and is the purpose to strengthen the slab or to keep the frost out?
* If it is to keep the frost out, will it really do that if its only 18" thick around the perimeter, with a frost line at 42"?
)</font>

The thicker edge is to keep varmits from tunneling under your floor & making it weak (air voids).

It will still be a floating slab, and it will still rise & fall with the frost. It is not a foundation, it does nothing for the frost line.

The thicker part will make it stronger, but not the primary reason for the rat wall. Keeping rats & etc. away is.

--->Paul

 

[bugstruck]

You are getting excellent information here but I want to throw this out there for consideration. At risk of starting a concrete additive debate (don't want that), some of us old-timers don't have much good for them. Retarders in very specific situtations, yes. Hardners, rarely. Air, virtually never. You can't make that "no additive" sale in the modern world, but the Romans had it right IMO. Yes, they had some geographical materials availability (binders) we don't even have in the US today and we have some they didn't. But their product longevity is indisputable and they did it with nearly zero reinforcement. The few failures I've experinced in Maryland supplied concrete were always with additives. Many newer bridge structures with the most advanced concrete mix designs were failing permaturely in the 80's and early 90's. Perhaps they have improved some, but I'm still seeing the same old list of additives. I'm just throwing it out to the younger crowd for consideration. If you haven't lived long enough to see the results, you'd do admixes to the 9's. They sure do sound good and I'm sure someone has done structural, weathering, .... freeze tests, but they just don't improve the base product in many situtations, assuming you handle and place the straight product properly. That's the most important quality conrol measure you can take IMO. Keep the water at mimimums for workability of course.

Other than my little digression on concrete, I know the recommendations presented for incorporation into this job are right on target. You can skin specific construction issues a few different ways, but virtually all of the methods discussed are very workable IMO.

HTH