# Post beam concrete slab help



## Turbofarviknugn (Aug 30, 2015)

I have purchased my land and will be building a post beam home on it as soon as my daughter finishes high school. It will be 40 x 70 with a 10' surround porch. I am just outside of San Antonio so permits will not be an issue. None the less looking for information on the slab design. The majority of bldg weight is supported by the beams of the building except interior walls. Question about conc beams and boarders, yes I am planning on lots of rebar. This is my remaining dele a.


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## Evons hubby (Oct 3, 2005)

Wherever the beams that support the weight will be needs to have a good foundation to support the weight. This can be poured with the slab but needs to be deeper and at least two feet wide. When I set up the piers for our log house I dug down to bedrock (1 1/2 ft) in squares three ft wide, laid up stone columns to set my logs on. All the weight of our house is supported by those corners.


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## Fishindude (May 19, 2015)

Difficult to answer with so little detail, layout information, etc.
This is something that would be wise to have a qualified builder or engineer familiar with the local conditions take a look at.

You don't want to cut corners or screw up the foundation.


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## Turbofarviknugn (Aug 30, 2015)

Sorry about being so vague, I was typing on an Ipad which I HATE ! The soil is a sandy loam, plamming on doing a concrete footer for each 5"x5" post before setting the posts in the hole with a minimum of 3' of post below grade. I am currently looking at using a company called Ark-La-Tex to construct the building, it will be a giant rectangle with 12' walls at the eves, framed out inside with 9'ceilings for rooms except living dining and kitchen areas. I will be using scissor trusses to get me a little more clearance for storage area above the living space. any info anyone can offer is appriciated. Dont worry I wont hold anyone to it, I have considerable residential construction experience with slab design ect just not in this type of application, I am thinking a 10' x 10' waffle grid slab with 2' beams all over would be WAY OVERKILL. Thoughts ?
Thanks in advance.


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## haypoint (Oct 4, 2006)

Scissor trusses will give you no storage areas. Did you mean attic trusses? Are you thinking of added storage way up high in the vaulted ceilings the scissor truss creates?


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## Fishindude (May 19, 2015)

OK, I looked up Ark-La-Tex.
What you are describing, and what they mostly show on their website are "post frame" (pole barn) buildings, not "post and beam" like you had mentioned in initial post.

Post frame buildings are very simple, and I assume since Ark-La-Tex is building it for you, they will take care of the concrete for the posts. Normal deal here is to simply auger a +/- 12" diameter hole, place a precast concrete bearing block in bottom of hole, set post on the precast block, then encase the post in poured concrete up to ground level. Unless you have crazy soft soils, that should work just fine.

Slab does not have to be anything fancy either if you have any kind of decent soils to build on. Never hurts to make the last 6" to 12" of fill directly under the slab compacted stone to assure solid bearing. 

A home and the garage will be pretty light loads on a floor slab. You are just talking about foot traffic, appliances and an automobile or maybe a tractor in the garage. Normal residential floor slab construction is 4" thick, 3500 PSI concrete with 10 ga wire mesh. Thicken the garage area up to 5" or 6" and go to heavier 6 ga mesh if that will make you feel a little better.

Around the outside walls on post frame buildings they typically nail a treated 2x6 or 2x8 "form board" with top edge at the level of the finished floor slab. To give a bit more of a foundation around the building perimeter, it's pretty typical to trench down 12" to 18" x a shovel width wide, along the inside face of the form board and pour a "thickened edge" with the floor slab.

A couple notes:
a. Put a plastic vapor barrier under the slab prior to pouring.
b. Pour the outdoor patio and approach slabs separate from the floor slabs, drop them down a little at the doorways, and slope away to shed water.
c. Have plenty of saw cut control joints in the floor slabs, so when it cracks, it cracks at those saw cuts. 10'x10' Grid is good for a 4" slab.
d. Stay away from the mixed in "fibermesh" reinforcement material. Ask for welded wire mesh to reinforce your slabs.


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## Turbofarviknugn (Aug 30, 2015)

Yes Haypoint, that's what I was meaning.
THANK YOU Finish Dude, that is the info I was needing. I was planning on using rebar throughout the slab on the spacers, DEFINATELY vapor barrier under the slab, what would the advantages of going with a higher PSI cement ? Totally agree with the slight down grade on the porch area.
Funny you mention "pole barn" vs "post beam" I regularly get corrected with whichever I call it. To me tomato to motto 6 of one 1/2 dozen of the other.&#55357;&#56835;


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## Turbofarviknugn (Aug 30, 2015)

Ahhhhh Post FRAME, that's why the corrections. Post beam is more the slots and wooden pegs construction, PHEW almost made it through the whole day without learning my new thing for the day ! :clap:


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## simi-steading (Sep 27, 2012)

I just got done pouring a slab in a pole barn about two weeks ago.. I did not use any wire, nor did I use rebar. I poured 5" thick, with a double layer of 6mil plastic for a vapor barrier. I went twice the thickness to help stop some holes as we walked on the plastic as we poured.

I had them add Structural F fiber to the concrete. That is fiber that is meant to replace using wire mesh. I used 4000psi concrete. Once poured, I covered it with plastic and left that in place for a week. I also pulled it back and watered it several times.

So far I have no cracks, and I've already driven my ford 2000 tractor on it.

I really think for a home, you are going way over board using rebar. Wire mesh may be one thing, but rebar is meant more for very heavy load bearing pours.

I see fisherdude says to stay away from fiber, and I wonder why? I've seen several slabs around here that were done with fiber, and they all look really nice with no cracking problems. I will say though, it is harder to finish.

THe biggest ordeal when doing a concret slab is to get your sub grade done right. WELL compacted and as level as possible with plenty of stone.


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## Fishindude (May 19, 2015)

I pour thousands of yards of concrete annually, so feel somewhat qualified to speak on this.

Fibermesh is nothing more than little short +/- 1" long fiberglass fibers that come in a bag and are dumped into the ready mix truck and incorporated into the mix. They are promoted as reinforcement to hold the slab together to eliminate the need for other reinforcement.
You see this stuff most commonly used in residential construction because it's quick and easy, and the residential concrete guys in many cases, frankly don't know what they are doing or talking about.

The primary factor in a slab performing well is having a well compacted, neatly graded solid base under it. Some good, compacted crushed stone is hard to beat. Many residential guys use pea gravel because it's easy to shovel, spread and handle, and it touted as not requiring compaction.
Think of your slab like a plate of glass. Lay it on top of a smooth solid floor that doesn't move and you can step on it without damaging the glass. Lay it on top of some soft carpet and then step on it and see what happens. The base material under slab is the key!

Regardless of the base, all slabs will eventually crack, due to expansion, contraction and shrinkage, if nothing else. To control the position of the cracking, we locate saw cut control joints in the slab, so when it cracks, it occurs on those nice straight saw cuts and doesn't look bad. Without the saw cuts, you get jagged cracks at places you may not want them. 

The purpose of wire mesh (and allegedly Fibermesh) is to hold the sections of slab together when they crack, so that cracks do not separate, open up, etc. Doesn't take a brain surgeon to understand that 10ga wire mesh with wires at 6" centers each direction will hold those pieces of slab together one heck of a lot better than 1" long fiberglass fibers smaller diameter than 2# fishing line. 

Further, if you take a close look at the surface of a Fibermesh reinforced slab, you will see a bunch of little tiny fibers sticking up. This makes the floor not as smooth, harder to sweep and clean, etc.

Slowing down the cure time after finishing is important too. The above posters method of covering and keeping wet is an excellent method. Slowly cured concrete holds it's shape better and achieves better strength.


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## simi-steading (Sep 27, 2012)

Thanks for clearing that up for me about why you aren't so fond of the fiber.

In my case, I shouldn't have too many issues of cracks getting too large because of it pulling apart. The base of my barn has a grade board all around it, and the slab is poured inside that. It probably will crack, but if it does, it really can't go too far because it's all contained.

Being as this was my first large pour (21 yards, 24x48 plus an apron int the barn) and since I had inexperienced help, plus only a couple other guys, I decided not to go with the wire since the slab is contains, and hence the reason I went with the fiber... It was just a lot easier on us... 

I still think the OP is going a little too heavy wanting to go with rebar....

I knew it was all about the sub base though.. I spent a lot of time compacting the dirt, then I used about 5" of #57 stone, then compacted that down for a few hours using a plate compactor... I don't see much settling happening in my sub base..


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## Turbofarviknugn (Aug 30, 2015)

Fishindude, THANKS for the input and I was doing a little fishing of my own HOPING you would reply to my thread just from your expertise. I am a Master Plumber by Trade 25 Yrs worth, and know when to seek input from people who have knowlege in areas I am un familiar, THANKS AGAIN. 
As far as the rebar goes I am standing by my guns on that, I only want to do this ONCE, I have been through foundation leveling and NOT wanting to go thru that again, a little extra effort and cost now to avoit problems down the road is worth it to me.

What about going with the HIGHER PSI concrete, is there any advantage to going that route ?

Thanks EVERYONE for your input !!!


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## Fishindude (May 19, 2015)

Do I think you need rebar, No.
I would go with wire mesh, but rebar never hurts, and it's not much money in the grand scheme.

3,500 or 4,000 PSI Mix will be fine for your slab, probably only a couple dollars more per yard to go to the higher strength. Again .... not much money in the grand scheme.

We typically find that if you do things right (don't add water, etc.) ready mix concrete in most cases tests out at a higher strength than advertised. Not unusual to have a 4,000 PSI mix test out at 5,000 PSI 7 days after pouring.

FYI -
I've got a 60' x 40' barn built in 1995. Slab is 4" thick, 3,500 PSI mix, reinforced with a layer of 10 ga wire mesh, it's on a good compacted base, and control joints were saw cut in the slab per "the book". We park automobiles in there and have worked on my 85 hp tractor in there. No odd ball cracks, slab still in great shape.


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## jwal10 (Jun 5, 2010)

I like the double rebar around the edges, mesh tied to it. My shop was 80'x120' at the farm, 3 drive through bays with rollup doors on each side. That is how we did it, 5" thick floor, 12"x12" around the perimeter, 24"w x 12" thick, right at the door openings. I have had D-8s on it with a 4"x12" plank under the tracks to protect the concrete, parked full loaded semis on it, no cracks other than hairline at the saw cuts between bays (1-24'wide, 2-20') cut every 8' the other way. I use double rebar at the approaches to all garages and carports, 1 around the perimeter, mesh tied to that. 5" thick for the first 2', 3 1/2" (thickness of 2"x4" on edge as form board) for the rest....James


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## Turbofarviknugn (Aug 30, 2015)

Thanks James, that's the stuff I am looking for.


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## miraclemant (May 28, 2011)

When I built my house, I not only put 6 mil vapor barrier under the concrete, but also put 2" rigid foam insulation. and WOW....... am I glad I did, we NEVER have cold floors in our house. NEVER........


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## Bearfootfarm (Jul 13, 2006)

Posts in the ground will rot sooner or later.

I'd set the posts on top of the slab to make them last longer and save on material

You'd still need the footers under them, but probably they won't have to be dug so deep


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## mreynolds (Jan 1, 2015)

Like BFF, I have done the same. Three years ago I built a party barn and we poured the concrete three foot footers OC for our posts. Then we placed the posts on the footers. How we fastened them was we allowed for 4" below grade and bolted a 1/4" steel plate to the footer. The we attached flat iron around the bottom of the post and welded it to the plate. Then filled it with concrete. that weld held a 36' 12"x12" post straight like an I beam until we braced it off. You don't need to go into the ground with post and beam when you are pouring a slab if you don't want to.


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## mreynolds (Jan 1, 2015)

Bearfootfarm said:


> Posts in the ground will rot sooner or later.
> 
> I'd set the posts on top of the slab to make them last longer and save on material
> 
> You'd still need the footers under them, but probably they won't have to be dug so deep


On that job mentioned above the first contractor had said they would get (if you can believe this) 50' 12" x 12"s and pole drive them into the ground 12' and then pour around them. I asked the owner where was he going to find a pile driver that would drive 50' posts and how much was that going to cost him just for one day to set up? 

I have pics of the final job but I cant seem to post pics of it. Any ideas?


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