excavation sequence

[Cliff_Johns]

I am considering doing the excavation for a new 1 car garage myself. (14'X20')

The city requires a 12"X12" beam on grade with a 4" slab. Monolithic
poor.

The land is very flat with the highest corner about 5" above the lowest
corner.

I'm thinking that I would
1. level an area about two feet larger than the garage(FEL).
2. dig 4" down for the whole area of the garage(FEL).
3. dig 12" trench around the perimiter for the beam(BH).
4. Put a 2X6 frame around the edge of the excavation for a form
5. Put in 4" of gravel everywhere - compact it.
6. Pour the concrete to 4" above the ground level

First, does this make sense? Is there a better sequence assuming you
have a TLB?

Second, I see three probelms that I'm not clear on.
1. How do I keep the sides of the excavation clean enough
to use as a form for the below groundlevel parts.
2. How do I get the concrete into the middle if I'm bringing
it in using Georgia buggys (very poor access area)
3. I have no idea how to excavate or form up the skirt.

Anyone have any advice?
Cliff

 

[beenthere]

After reading the following posts, I understand what you are getting at. Thanks to all. Never heard of this floating pad with thick edges referred to as having "beams", but now I have.

And thanks for the thread, as it gives me the ideas I need to pour a slab for a shed.

"I will admit that your descriptions have me puzzled. Hope others can help more than I, as I only have questions."

Cheers /forums/images/graemlins/smile.gif

 

[jimg]

I think I understand...the slab would essentially be supported by the 'beam' on all sides which would look like a large upside down pan. If thats correct then I think youd need forms that go to the bottom of the beam pit and project up beyond them by the thickness of the slab. Theyd be anchored from the outside.

 

[BB_TX]

I put up a 30'x40' building several years ago. I had a concrete contractor do the slab. I tried to watch as much as I could but did not see it all. Here is what I think he did.
I had previously leveled it, but I think he leveled it some more,
He marked the boundaries of the slab, and dug the trenches for the beams. The trenches were at least 2' deep, maybe more. And he also dug crossing trenches front to back and side to side for additional beams. I saw the BH but did not see him using it. But the trenches were almost perfectly dug with smooth clean sides perfect for forms.
He then filled the area with cushion sand, rather than gravel.
Covered that with black plastic.
Layed the rebar for the slab, and extra heavy rebar in the beams.
He then set the perimeter forms. I don't remember for sure but I am thinking they were 2x10s or 2x12s. He had to do that to get the 4" slab above the sand.
In my case, the trucks could drive right up to the site. However, I remember a thread just this week or last week showing someone using buggys to pour concrete inside a pole barn. I could not find that thread though.

 

[Knute]

Out here they call that a "thickened edge slab" when we had it done for our garage a couple years ago.

In our case the area was leveled, a 18" trench was dug for the edge (18" required by code here) then gravel and rebar for the slab base and forms around the outside from ground level up to 4" for the slab. The forms did not go into the trench.

 

[bebster]

Beams on grade I've seen are 12" square with 4 pieces of rebar running horizontally through it, 3" in from all corners. It would seem to me that you'd want to form the beam with 2x12's all around the outside. Nail them together well and backfill the ground on the outside up to the top of them to keep them from blowing out with the weight of the concrete. The bottom of the beam would be the compacted ground beneath.

Typically there is 6"x6" wire mesh reinforcement in the slab.

Once it's all formed up and the mesh in, you can pour. You should be able to pour right into the 14' side. You'll probably have to climb in with boots on to pull the concrete to the center (only 7' from the edge). When you get 3" of concrete in the beams, add the first 2 horizontal rebars. When you get up to 9", add the next 2 rebars. Finish the pour, and finally, finish the top surface with a float.

 

[Ronbo]

I poured a 40X40 slab and will be adding anouther 40x46 fot to it.

The dirt was leveled. Sand put down. 12x12 beams all around. Black plastic. Rebar. Forms were only above grqade. It doesn't matter what the edge looks like below grade. Dirt was piled against the forms to help hold them. Bracing at least every 2 ft for the forms.

Did not want to hire a concrete pump, so the workers built a trough with 2x6 and metal siding. Really helped to move the concrete.

Ron

 

[Cliff_Johns]

Thanks everyone for the helpful discussion. It sounds like my
strategy for excavation will work out fine.

I'm still a little wary of pushing the concrete from the edge to the middle.
Sounds time consuming and sounds like a lot of work, but I can't see
another way to do it. I'll have to buy extra beer for the crew.

Anyone have any advice about shaping and putting forms on the entrance
skirt excavation? I'm thinking 9' wide to match the door and maybe
three feet long? Can I poor that as a separate piece. Sounds like it
might be a good idea, but I'm not sure.

Cliff Johns

 

[OkeeDon]

Terms vary around the country. Never heard it referred to as beam on grade; we just called it a slab with footer; what make it monolithic is that they are all poured together as a unit. The size of the footer, or beam, depends on local code, as does the number and placement of rebar in the footer. The rebar is held in position by sitting on saddles so it will be encapsilated on all sides.

You have the basic sequence correct. Here's a picture of the excavation that might help you visualize the details.As for the buggies, I guess you start at one end and work to the other.

 

[Junkman]

A few years ago, I poured a apron to my garage and the fellow that did my driveway said to just remove the top soil and pour the concrete on the undisturbed earth. I formed the edge with 2 x 6 lumber and used rebar to hold the "forms". Two winters later, no cracks, no problems. I suggest that you consider doing the same thing. Remove the top soil to the depth that you need the floor and pour a thicker floor. Use a 3500# mix with fiber glass along with the rebar, and 6x6 wire mesh. Pour a thicker floor and you will be happier with the end result. Think of the savings of labor going into the materials. Just make sure that you have a few people that have worked concrete before. If everyone is green, then don't even think of doing this job. You will be better off hiring a professional. If you hire the job out, you will also get a smoother finish that will also be more consistently level and true to grade. That is why they are called professionals. I understand that some people think that they can save money by doing it themselves, but there are times that someone else can do a better job faster and less expensively than the homeowner. Just remember that if you mess up the job, that you will live with the mistake for the rest of your life. When I added onto my garage, the contractor that did the job, is a concrete man. He hired the job out to someone else because they could do it faster and better than he could with his crew of carpenters. Carpenters make lousy concrete men and concrete men make for lousy carpenters. Many times homeowners make lousy carpenters and concrete men, but fail to realize this until they are over their heads. Get some prices first and see how much you will save by doing it yourself. Remember the garage is only as good as the foundation you build on. If the floor isn't level, then the building isn't going to be level. Everything depends on the base being true and accurate.
If you decide to do this job, I suggest that you consider renting a laser level for setting the forms and determining the floor depth as you work the concrete in the areas away from the forms. Otherwise, you will not know if the center is higher or lower than the outer walls.