Info on pouring a slab for Barn.

[zukgod]

We are starting a new project and could use a bit of help.  I have only done concrete work once a long time ago.  We are going to pour a slab type foundation.  Has anyone seen a how to online?  I am going to pour it at 4inches deep, but other than that I am clueless.  We are in Washington state on the westside so freezing is really not an issue.  Anyone want to walk me through the process?  I have searched but can't find a how to.  Thanks in advance for any help.  Size will be 24x32.

Josh

[glenn-k]

I've only done about 300 of them-- maybe I can help. :-/

Tell me more about the building going on the slab - general info below.  Note that steel bldgs. have main frames with non-bearing walls between.  For a small barn I would still use the thickened edge footing myself, even if a bearing wall.

I'll assume slab on grade - ground leveled - organics removed.  Ground solid -natural soil.

I would form up around the outside w/ 2x4's using long stakes so you can dig at least a 6"x6" shovel footing - or thickened edge as it is sometimes called.  Put 1 #4 rebar around the perimeter - lap at least 20 bar diameters or 10"  - probably best to add 6x6-10-10 remesh or fibermesh to the slab for most strength.  
This is for Non-permit ag use general specs.  If inspected it may require bigger footings.

If it is a steel building it will require footings about 2'x2'x 18" at each leg of the main frame - smaller at the endwall posts and 20' hairpins to tie the mainframe legs into the floor slab.

12"x12" by length of door plus 2' is good under big door openings for tractors - trucks etc. is also good.

Slope big door openings about an inch per foot tapered to a inch or so behind the door to prevent rain from going inside the building during storms - it runs off the face of the door and can go in or out depending on the slope under the door.

[zukgod]

Glenn

 Thanks for the info.  The slab will be built on the bare ground all vegatation removed.  I am thinking of putting down a few inches of gravel and compacting it with one of those vibrating things if I need it.  This will be a stick built barn without permits.  So I will need the trench around the outside edges.  I would have built a pole barn but I got a really good deal on 2x6's so it's cheaper this way.
A few questions,
1) Do I need the compacted gravel on top of the dirt?  We hav very soft sandy soil.
2) Do I need to put stress reliefs in the pad?
If you can think of anything else a novice like me could screw up please let me know.  I really appreciate your help.

Josh

[youngins]

Tony has some good info/pictures when he built the slab for his shelter:

http://n74tg.blogspot.com/2006_07_30_archive.html

[glenn-k]

If you want to level the top you could put just a layer of sand on the top - set your forms level then make a screed board 3 1/2 or 4" as you desire.  Nail a stake on each end of a board to put on your screed so the bottom is level where the bottom of the concrete will be.  You can then grade the sand level - cut the high spots and fill the low spots.  

Sand leveled then wet is fully compacted.  There is not much you can do about the soft ground except reinforce the concrete more or make it thicker.  In general if you got the organics off and are on undisturbed soil it should be OK.  The 6x6 10-10 remesh or 3/8 rebar on about 18 inch square centers would help in that case.

A road base - usually clay gravel mix on top of the ground under the pad could give you a firmer base at a price.  Depends on what you want to spend.

Concrete will usually crack if it wants to so putting some kind of weakened plane joint can stop the crack or make it just crack neatly where you want it to.  You can do it with a jointer in the wet concrete - use a plastic strip called zip strip - old stuff was tin called Key-Cold, of pour on separate days dion smaller sections.  If you do one big one you can get a dry diamond blade for your skilsaw and cut it the next day after it hardens - cut about an inch - 2 passes if necessary down a chalk line snapped on the floor.  I usually go no larger than 20' x 20' or smaller sizes that will look good with the size of the slab.  You could go 12x16 and have slabs that would probably not crack in other areas.

Break it into manageable sections ot pour and screed.  Will you have professionals helping with the finishing?  Have enough people to rod as the concrete is poured - one shovel man pulling down in front of the screed and filling holes etc.  One running chute.  That would be a minimum if some were pretty good with concrete - 5 or 6 would be better with at least a couple knowing concrete and able to direct the show.  Check with the concrete company for guys that might want to do a side job helping you.

[zukgod]

I think I can have 5 hard workers including myself, but none that are concrete people.  I will call and see how much someone might charge for a side job to help with the pouring.  So are you saying I should brake it into different sections to pour or can I just do it as one big pad in one pour?  I really appreciate your advice this is a huge help.  I will order the fiber in the concrete as well as get the rebar in there and the square fencing looking stuff on the bottom.  Then put sand on the bottom.  Thanks again you don't know how much help you have all been.

[youngins]

Glenn,

Would poly on top of the sand be a good idea as well?

I am referring  to John C's reply in a previous post: http://www.countryplans.com/cgi-bin/yabb2/YaBB.pl?num=1175193331

[glenn-k]

If you attempt this in one big pour by yourself with no pro's helping I will want to go over all details of the pour with you.  It is quite a bit of concrete for an untrained crew.

How soon do you plan the pour?

As Youngin's questioned, a vapor barrier of 6 mil poly can be put under the concrete -- common in houses -- not so common in shops.  It usually has about 2" of sand over it.  Forms would be set higher to compensate so probably 2x6's would be used instead of 2x4's.  Sand would be screeded and wet down as mentioned above to give uniform thickness to the slab.

How is access for the trucks relative to the shape of the building - the 24' way and the 32' way.  Which sides can trucks get to?

When pouring you must keep up with the truck - keep leveling - screeding - bull floating - edging - all done as it is laid down.  You can ignore some of this but it may come back to bite you as all of the sudden the concrete starts setting fast and you are not ready.  Hold the truck a bit as the guys catch up.  Better to pay a bit of wait if necessary than to dump a big unmanageable pile of concrete and have it set before you get it dowm.

Tools you will need.

Bull float and handles to reach over 1/2 way across the slab - wood or magnesium x 4' long appx

Fresno Trowel - similar to bull float in size but steel for putting a final finish on large areas

Weight for trowel and float - we use a piece of I beam - other things that will stay on top could work

Hand trowels and floats - steel and wood.  Swimming pool trowels are easier to use for inexperienced - they have rounded corners and are quite flexible.  Wood or mag floats with a bit of water if necessary help to re-work the surface and take out imperfections.

Tamp - a tamp can help smooth out bumps if you have to go into th soft concrete for any reason.  It may not need to be used if things are well planned and bull floating is done immediately and kept up with.  

The bull float is used like a wood plane only bigger to pull off bumps and fill holes from the outside edge of the forms.  It leaves a rough surface which dries faster.  

The Fresno trowel smooths and seals the surface to put on the final finish and make it dry a bit slower.

All processes must be kept up with before you need it - if you wait until you need to do it , and haven't done it it may be too late.  A power trowel on standby can take care of many problems but is not necessary if you keep up with the hand work on this size slab.  

Most of these tools can be rented,  Check at a local rental agency if you have one.  Check on a 3 foot power trowel for safety if you want also.  It can be practiced with on dirt to learn how to run it.  

More to follow as you get more questions and you answer the above questions so I know about your setup.

[John_C]

I don't have anywhere near Glenn's experience with concrete, and most of mine was in the FL Keys where the high temperatures and pourous coral rock cause concrete pours to be fast paced affairs.

I might still be inclined to put some plastic down.  It's not necessary but it might keep the ground from sucking water out of the concrete and thereby slows things down.  Except in very cold temperatures I don't remember anyone ever complaing that the concrete cured too slowly.

[tc-vt]

I was also planning a monopour slab and then decided to divide it into two pours.  First I pores a perimeter wall which was 2 feet tall and 18 inches wide.  During this pour all you need to concern yourself with is that the walls are reasonably level and to get your anchor bolts in their proper places.  

Then I stripped off the inside of the forms and compacted fill inside the perimeter wall and then poured the slab inside, flush to the top of the perimeter wall.

Splitting the foundation into two separate pours split all of the concerns (level, anchor bolts, finishing the slab surface, working the mix into the forms, etc.) with a pour into two separate events.  I would do it this way again.

Also, the pour was done pretty wet, or, 'self-leveling'.  Sure it's not the strongest way to pour concrete but you won't be so concerned about going around with a vibrator or a mallet to get out air bubbles so you can run around like a lunatic worying about other things.  There was absolutely no honeycombing when I stripped off the inside forms.  The vibrator I rented never got used.
Pictures at
photos.yahoo.com/ny2vermont

Tom

[zukgod]

Tom,

Great pics.  It seems like a bit more work to pour in 2 pours but looks like it may be worth it.  I just don't know, now I am getting worried.  I think I will try and get some help with this thing I don't want to mess it up.  If the foundation is bad the barn is worthless..

[tc-vt]

There's good reason to be scared or worried.  If the pour goes wrong like a form blowing out, it is a major disaster.  I had lots of anxiety over this.  For the several days prior to the pour, every day I woke up and looked at the forms they looked less strong than the day before so I added more bracing, day after day.  Then, my helper told me he couldn't make it the day the mixer was coming.  I fortunately found more help at the last minute.  During the perimeter wall pour I heard a strange noise that sounded like wood creaking.  Before I could panic too much I saw it was someone's shovel rubbing on the rebar.  It was definitely the part of the project most demanding omn the nerves.  I will remember the sense of relief and my pizza and beer dinner that night for a long time.

You could look into subbing this part out or find some guys that work for a cement contractor who want to moonlight on a weekend and provide the help.

Tom

[zukgod]

Tom,

 Thanks for the advice, I have been waking up in the night just thinking about this stupid thing.  I really don't think it is out of my reach to do myself, I have done one other pad but it did not turn out perfect, but I know what I did wrong.  I have it all formed up, and will add the bracing Saturday then Monday I hope to get the concrete in.  We shall see what happens.

Josh

[glenn kangiser]

Anything else I can help with, feel free to ask.  Did you get your tools together?

How about anchor bolts -- Do you have them - are they ready to set - are you going to use templates or hand set them?

You should be a little more than 10 yards so it shouldn't be too bad.

[JRR]

Go a bit overboard to treat the mixer truck driver well.  If the weather is cold, have hot coffee or hot chocolate ready ... If the weather is hot, have iced water or soda pop.  Wet concrete is heavy.  The driver can save you a lot of muscle effort by directing that chute with care.  Also you may want him to "tighten" (add cement) or "loosen" (add water) to the mixture ... better done by a "team player".

Don't offer cold beer.  You don't want him losing his edge ... or getting back on the road tipsy.  A gift of warm beer hopefully won't be used 'til he has a chance, later at home, to ice it down.

Make sure you get his name ... you may want to ask for him by name if you have concrete needs later ... no need for someone new to have to learn the way to your job site.

[tc-vt]

I just thought of another thing I did that was a good idea in the end.

Estimating a pour can be fairly easy for a stem wall or a slab.  You want to add 10-15% to your calculation, maybe up to 20% for a very small job.  Too much cement is no big deal.  Too little will really ruin your day - and your foundation.

There is probably somewhere else you can use cement.  I formed up for a small 8x10 slab where I could later build a shed for one of my two pours and made a 14x10 slab for working on the car for my other pour.  Barbecue foundation, steps, sculpture, etc.  Calculate this extra little project into your estimate.  Then add your 10-15% fudge factor.  Pour the house first then your other project.  .  Now you know you have enough cement to get the foundation done.  If you estimated wrong, worst thing that happens is your project slab gets screeded out thinner than you estimated.  It cost more, but it is good insurance against a possible brain cramp that results in you estimating your needs incorrectly and you get a second little project out of the deal.

Tom

[Amanda_931]

Tom wrote"

Too much cement is no big deal.  Too little will really ruin your day - and your foundation.

There is probably somewhere else you can use cement.  I formed up for a small 8x10 slab where I could later build a shed for one of my two pours and made a 14x10 slab for working on the car for my other pour.  Barbecue foundation, steps, sculpture, etc.  Calculate this extra little project into your estimate.  Then add your 10-15% fudge factor.

Good thought.

Probably more important with concrete than most other things, but adding a fudge factor or enough to do something else with works for a lot of raw materials--from lumber to fabric for a quilt.

[MountainDon]

The one concrete job I contracted out here ran into this very problem. The "pros" had misgauged the concrete and even after scraping up all the spillage were a little short. It was fortunate that I had 2 bags of Quikrete available. Almost any other job if you're short it's an inconvenience at worst.

[glenn kangiser]

My guess on this one is that there is no way that Josh will get enough out of one truckload unless his floor is set at 3 1/2" instead of 4" and even that would be tight.  I think he will have to get a small clean-up, but even that brings up a good point.  

Estimate the exact cubic footage you will need on the cleanup - divide by 27 for cubic  yards and add at least a half yard.  Try to work your pour out straight if possible so it is easy to calculate the cleanup footage.  4 inch concrete covers about 80 square feet per cubic yard - don't forget footings.  Many times the concrete company will bring a small cleanup load for little or no fee besides material cost, but make them go twice and you will likely pay dearly.  More and more I am seeing pretty substantial fees for travel too though.

[JRR]

Having ready forms to pour with the "extra" concrete is a good idea.  If planning a block wall, I like to have forms and re-steel in place ready to make door and window lintels.  

Other ideas might include forms for: fence posts, park bench end-pieces, paver stones, etc, etc.  I once used an old outdoor grill top and a short length of plastic pipe (as a void) to make a circular base for large table umbrella ... the wind has never nudged it a bit.

[zukgod]

I could not get them to come out until next weekend.  So I have extra prep time which I am sure will come in handy.  I think right now I am estimating 10 yards, but have a concrete guy coming out to tell me for sure, then I will add 15-20% per your suggestions.  I will keep you all up to date.  Everyone has been very helpfull and I really appreciate it.  

Josh

[glenn kangiser]

If you empty the first truck then call or have the driver call in the balance for the cleanup you can usually get it closer.  I usually go about 1/2 yard extra if its a straightforward estimate.  Alternatively the trucks that mix on site just give you what you want then take the rest back dry -- not all companies have them though.

[Bill]

There is a good narative of planing for and constructing a 24'x30' slab for a barn in the book Building a Multi Use Barn by John Wagner. I found the book to be very helpful.

Bill

[Okie_Bob]

I'd just like to add that this is one of the toughest jobs you'll encounter while building your place. I'm talking about hard manual labor and there is no time to rest up once you start.
I built a 24' X 50' garage/aparment on a 6" slab. I did all the prep work, built forms, wired rebar, etc, everything. Then I got scared and went to the redi-mix plant and asked if they had any references of guys that would do the actual pour and finish. Thankfully, they did and it was one of two best ideas I had building my place! This guy showed up early with 5 helpers and two finish machines. This was a hot Texas day in mid August and hot as hell. They worked a good 10 hours and the pour was perfect when they left. It cost me $650 and well worth it. Some things are best left to the pros and this is one of them!
Okie Bob