Thinking of getting a building put up. It's a enclosed carport basically, but it seems a good way to for budget reasons.

I plan on doing a slab but have a few questions.

Is 4" a standard garage thickness?

I don't want to have to deal with block and all, I was thinking of a footer/foundation monolithic pour. But how deep would I need to make the sides/foundation?

Rebar needed? Wire mesh thru the main body? Rebar thru the whole body?

What about running rebar up thru the foundation and across the pad, tying it all together?

Base? 4" of gravel (crushed then compacted)? More or less?

Probalbly have to excavate a foot or so along one side at the base of a hill. Any issues there? Compact the earth as I level my work area?

I've been surveying for a long time, but have not paid attendtion to how garages and other slabs are really poured. I know I can get it level and square for sure, set it up too, but I need some info. Then I could get a bunch of labor help and get her done.

And before someone flames me, Yes, I've looked at having it contracted out. Cheapest so far is $6500 and that's from a guy who does mostly walks and patios. It just goes up from there.

Thanks for any input,
Blair

 

4" is fine and used commonly unless very heavy vehicles/equipment will be used on it.

Footer depends on type of building and soils but 12-18 inches is common. I work for a builder and on slab built units they range from 12-24" depth depending on the load.

I would pour the pad and footer seperate so you can put and expansion joint between the 2 less chance of cracking.

You can use wire or rebar or use fiber concrete that has little pieces of fiberglass in it to give it strength. On slabs for house we use fiber instead of wire.

As far as cost goes it will be alot more now than it would have been 6 months ago thanks to the gulf coast hurricanes. I think around here its up to $105 bucks a yard.

As far as doing it yourself, you need to determine how much comcrete you will need and then determine how much the contractor is charging to do the pour. Special eqipment is needed that you would have to rent.

 

The depth you have to go below the ground depends upon local codes and the frost line. Your local codes department can tell you what that is in your area. Don't skimp on depth.

A 4" pad is OK but you should go 5" if you use #3 or #4 rebar. Rebar is better than mesh since it is easier to get it into the center of the concrete. Mesh tends to get mashed down and not pulled up properly even when professionals do it.

According to most everyone that has tried it... DO NOT use "fiber" concrete for a garage floor. It will leave a "hairy" finish that will drive you crazy for years (do a search here).

If you are going to try to do this yourself place the footings first. Then place the concrete slab in 4 sections one at a time. Finishing a large slab is very difficult for beginners. If you do this during hot weather the concrete will set up VERY rapidly.

You can caulk the joints between the sections with urethane sealant later.

Good luck and try to find some experienced helpers.

 

Thanks for the replys. I figure if I got enough help, I can get it done. When laying the rebar, what about supporting it from the bottom to keep it in the middle of the slab?

Maybe some vertical rebar, then tacked to the crossing rebar?

You mentioned several pours for the main slab. You mean pour one and let it cure, then pour the next one and so on? Split it up over a several day period?

The building load itself won't be great for what we are planning, but I think frost depth would be something to pay attendtion to.

Have to check with the codes office.

I'm thinking hard about excavating it myself, then the forms and rebar myslef. Possibly the footer, then go talk to one of the crews in the local new neighborhoods for a cash pour. Either that or get a couple friends and possibly a few day laborers to do the job.

We plan on doing this in the cooler months. Preferably soon. I don't want to wait for spring. It will be really wet.

What special equipment are you talking about? I watched a crew pour a garage slab here yesterday, they had the rebar in, wire mesh too. There were four of them, they shoveled it to the corners and around the edges where the chute couldn't reach. Then they let it set a few minutes and used hand held bull floats to smooth it. Then they came back and hand trowled it. I never saw them use one of those things to jiggle the concrete to get the air out. Is that just on big slabs like for commercial stuff?

Thanks for your input guys.

Blair

 

ideally u want the reinforcement about 2" from the bottom of the slab, the lower in the pad the more weight the slap will take

 

I did mine pour 3 months ago, concrete cost $100 a yard. I did a monolithic pour, code here is 18" deep, 12" footer (bottom) angles up to 16" and 4" in the center. Mine is almost 6" in the center and I used #3 reber 12" on center going front to back and sisde to side. Also put some in the footers horizontally and used shorter lengths vertically to tie everything together. I had some mesh laying around so I tied that to the rebar as well. Overkill. Rented a machine and compacted the ground one weekend let it sit a week for the city to inspect then compacted it again before adding the rebar. I did it all myself until the pour, it was hot and had 5 people and it wasn't enough. Should've had 7-8 to switch people in and out. The part that was is the sun setup way too fast. They have craddles that the rebar sits in but I just set them on pieces of brick that was from an old fireplace. Make sure to plenty of stakes around the form it would be bad if a side fell down because of the weight of the concrete. It was the first time any of us did a pour that big (24x24) and we made a few mistakes, but I'm happy with it and that's all that counts.

 

Just poured a garage foundation with a 20x30 main part and a 19 x 16 guest room part.

Footings were about 24" deep. At each load supporting point, such as the openings for the doors, and places where load bearing posts were going, a 2'6" x 12 pad was poured. Slab was 6" for garage, 4" for the living area.

In the garage part, I used a raised curb to build the walls on. The living area is flat slab.

Per the city approved plan, the site was covered with 4" of sand, then 10mil plastic, then another 4" of sand, then the rebar on dobies.

Pads and footing trenches had rebar cages bent up.

Tie-down bolts were placed along the edges, as well as saddles for the 4x4 posts where specified.

Since Simpson Strong Walls were going to be used, their tie down bolts (4 per wall, 2 big, 2 much bigger) were put in place using the metal template to locate the bolts so the predrilled wall will go over it.

This was a monolithic pour and was just about 40 yards. (!!) Finish was good but the last 4 yards was late and I have a cold joint that I'm not pleased with but it's a garage so it will stay.

They had about 5 guys, plus 2 on the pump. Plus a machine.
If you are digging into a hill side, dig some more so you can route the down-hill drainage around the building.

When we have our next earthquake (CA.) I've told the kids "Head for the garage!!!"

 

Chunks of patio block or concrete brick works real well to support the rebar. You want the rebar 1.5-2" from the bottom of the slab. If it is tied to vertical rebar it will just get driven into the ground or slip down and you won't be able to lift it back up.

Place the floor in 4 sections so you will not have too big of a section to finish at any one time. Let each one cure for a few days b4 doing another one. If you have a big experienced crew it could be done all at one time.

 

Real Dobies are small square blocks of concrete with a couple wires cast in them, so you can tie them to the rebar. They don't cost much, but I usually ask for broken brick when I'm at the mason supply and they give them to me for free.

It's a good idea to have at least one person on the job with experience when you pour. If the conditions are right you can have the driver wet mix at the top for more cream, but if it's too wet - not good. If you can hire a guy or two on a side job and have a few friends that can help, things go pretty smooth.

When you call for pricing on your concrete, tell them what it's for and between the batch plant and the driver, they can give you a mix that you won't need to vibrate. The thing about it, to get the full structural benefit of the concrete, the mix should be thick enough, (google concrete slump), that a vibrator should be used. Thining it out, without vibrate, is kind of a corner cutter, but a lot of guys have the experience to get away with it.

Much has to do with your base material. Put down a few inches of 3/4"- rock, compact, then a few inches of sand, compact and you might only need steel mesh. Depends on the soil and the load. I like rebar.

Years ago I worked for this old guy, (in his 70's, 55+ years in the trades, over 1000 big jobs), and every concrete job like this was a base of 4" rock, followed by 3/4", then sand/plastic/sand. Compact at each step so much, guys wanted to quit. Steel mesh at this point worked fine, because the base was solid. It was a reputation thing for him. Even if it was a commercial building that might only see the weight of a desk, he liked to tell the customer they could drive anything they wanted on there. If you see guys that aren't using a vibrator, you probably missed the all the compaction work they did. Myself, I'm happy with a little rock, sand and rebar..

 

Make sure there is at least 1.5 times the diameter of the rebar used covering over the top of the rebar or you can have problems later with rust stains or cracking on the surface. Same goes for below the rebar also. Your local codes officials can verify the dimensions for your job. The requirements may vary in your area.

 

four inch is the normal, but most form with 2x4 which is 3 1/2. 2x6 forms would be better. we recommend a 4000 psi mix, but a 4500 psi is only a couple dollars higher and you can pour at a 6 inch slump which is more managable and still have plenty of strength. the mesh and the rebar only hold the concrete together when it cracks so either will work, i recommend the rebar on bricks or chairs 2/3 depth of concrete. i would put a drain pipe above the slab in rock to drain water from the hill. the concrete will only be as good as the base it sits on, compact well. 3 people should be able to handle 8 yards easy enough. leave rebar sticking out of one section to extend into the next section to prevent any raise or drop between sections. if i can be of any more help just ask. i run a concrete plant. by the way concrete is poured for about .50 sq.foot around here. tr

 

Rob,
.50 / foot, wow that's cheap. Around these parts it's as much as $2.00.

I just poured 35 yds. in my driveway and back walk. 4500# mix, 6" thick on all driving surfaces, 4" on walks, wire, and fiber. I know it's kind of overkill but I hate doing things twice, and I hate cracks. All poured in one shot (not recommended for those who don't have experience). Slabs and walks were saw cut after pouring, then acid stained for color.

 

Thanks for the replys.

We still intend to do as much if not all of this ourselves.

Right now, after talking to Planning & Zoning, I have to submit a scale drawing of my intendtions, basically a location survey of the house, showing the driveway and external features of the property, well, fence, deck, porch.

I then show the proposed garage area, with grading contours of future grades and existing grades with spot elevations. Good thing we have spare total stations sitting around. Make this part alot easier.

For those of you who have offered lots of help, bookmark this thread, and as I get going good on the forming, I can post pictures and I'm sure I'll have questions.

It will be a couple weeks,
Thanks,
Blair

 

2.00 ye-ha people would die around here. sounds like you had your ducks lined up. i used to pour alot of concrete, but i got old. it's just now getting the right weather to pour around here.

 

USE FIBER MESH! Not using that is like prefering an outhouse to your bathroom. The strength it offers is is way too important to ignore.