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.

 

[Egon]

If you have to use wheelbarrows run them around on some planks and dump where required. Remember that the concrete truck can come out with extra chute.

On the entrance apron a slope would be nice so rain doesn't run into garage. Have you considered paveing blocks for this area?

If no lazer level a string line about about a foot above the finished grade can be used to measure from. Means wading in very fresh concrete.

Egon

 

[MMILLER]

I don't no about pushing concrete it seems a lot easier to pull it to you you using a garden rake. If you are going to use mud buggys you need to start on the sides pull concrete towards middle. But only do an area reachable by rake. Go to other side dump concrete and pull towards center. You need to work side to side and back to front only work an area you can reach by rake. People working with rakes should also work cement by pushing down on top of cement with rake up down motion, to work out air pockets and semi level. Make sure you rent a bull float with extensions to finish floor. I would not pore apron at the same time as floor. This should be poured with an expansion joint at main slab because this wil be outside. You definitly do not want posible weather to cause problems with main slab. It is easier in future to replace apron in future if you have problems if it is not conected to main slab. Also it would be quicker if you plased rebar in form before pour hardware stores have alumnium stakes you can buy to place in ground (no rusting) to support rebar then wire rebar to these at distances you want. I don't no about where you live but here in central PA. they only allow so much time to get x amount of concrete off of truck. You will need a good crew with everybody having an idea about what they will be doing. Also if these are volunteers make shore you get a couple extra if possible. In case somebody calls up day of and can't make it.

 

[bebster]

If you mean an apron in front of the door that sticks out 3' from the entrance, I'd pour it separately. You'll want it to pitch away from the garage for proper drainage.

 

[Junkman]

I will second that suggestion as to pouring it separately, but I would also set 5/8" rebar into the floor where the door is located extending out to where the apron is going to be located to hold the apron from falling or pulling away. This is accomplished by drilling holes in the framing lumber and sticking it into the holes when the floor is being prepared. It should be bent down the last 6" at the floor end in a hook like fashion. It should extend about 2' into the floor and about 2' into the apron. This is important to keep the apron from moving away from the building in later years due to settlement or frost. I like a broom finish on the apron for traction in winter and to keep water moving off during rain in warm weather. Some people put a depression in the concrete floor at the door to keep rain from coming under the door during driving rain. I have never done this, but I can see the advantages. I am not certain of the procedures of how to do it properly, so I can't be of any help to you on this aspect. I don't believe in sloping floors, because I have never seen a floor that would have enough water on it that a slope would be of any benefit for the water to run off of it. If you have that much water on the floor, it is called a flood and the slope won't matter. Besides, if you slope the floor, it all would have to slope to the door in all directions to be effective. It just isn't necessary in most cases. If you had one bay that you were going to wash your car in, I could see that one having a drain in the middle, but you would need to slope the entire floor toward the drain like a shower for it to be effective. That would mean 1/4" per foot from the sides to the center for that bay. That is a lot of pitch!

 

[Cliff_Johns]

Thanks for the picture Don, that cements the idea in my head. (of course
there was a lot of cement in there already.)

This discussion has been most helpful. I got one professional quote
that came in a $1,800. Sounded like a lot to me. I want to get a couple
more. But my advantage is that I have a friend who used to do
concrete as a summer job and another friend who just installed a
large concrete patio. I figure 8 guys ought to be enough even if one
backs out at the last minute. I haven't gotten a quote for just the ready
mix delivery yet.

Mostly I want to do it myself so I can learn about excavation, and about
concrete, and I want an the extra excuse (I mean, reason) to buy a
nice 4110 with a loader and a backhoe.

Anyway, thanks for all the discussion. It is helpful and empowering.


Cliff

 

[jmc]

Don,

Chamfering those inside edges looks like a good idea. Nature abhors a sharp corner as well as a vacuum!

John

 

[Junkman]

Make sure that you compare apples to apples and that the quote you get on the concrete materials is the same as the contractor was quoting on. Too often contractors quote on a lesser grade of materials to keep the price down. Don't skimp on the quality of the concrete. The price differential isn't enough in the end to make the difference, but the difference in quality of the job is. One thing to consider is the type of finish that you will have on the floor if you do it yourself or have it done. Many concrete contractors will use a power finisher that has the ability to give you a very smooth finish, which you cannot duplicate without the machine and the experience in operation of it. I like a 3500# mix with fiberglass, 6"x6" wire, and rebar where needed poured 6" at the edges and 4"-5" in the middle with plastic barrier underneath.

 

[Cliff_Johns]

</font><font color="blue" class="small">( Many concrete contractors will use a power finisher that has the ability to give you a very smooth finish, which you cannot duplicate without the machine and the experience in operation of it. )</font>

That's a good question. I don't know what finish I want. I was thinking
a light broom finish, so I wouldn't slip if I got a little oil on the floor.
Do you think a smooth finish would be better? Perhaps easier to clean the
oil off of, which is also a way to keep from slipping, I guess.

I will be keep a my tractor, lawn tractor in it, and also have some
tinkering space if I learn to weld etc.

Cliff

 

[Junkman]

My parents garage had a broom finish and it was always dusty, held the mud from the tires, difficult to sweep, and you could never get the oil stains off of it. I have a smooth finish on the garage floor and oil stains come up with some speedy dry and a rub of the shoe. It sweeps clean and I don't find it slippery unless it is wet and I am wearing leather soled shoes. There is no way that I would consider a broom finish and I know how much work it is to do a concrete floor. I have seen them done and I know that the contractor does earn his money that day. Some projects are worth doing yourself, and others are just brute labor. Concrete work is brute labor. I rather let someone else do it. I have learned that I will do that which I can do over again without much of a problem. If you mess up a concrete job, you have no choice but to live with it. To me, that isn't a very good option. If you cut a piece of lumber too short, you can always cut another piece. If you don't build the wall correctly, you can take it down and rebuild it again. You can't do that with concrete. If the concrete isn't level, the wall isn't level. Everything depends on the foundation being correct. A 1/4" mistake at the bottom can cause many problems in the building of the final structure. The foundation of the building is the most important aspect. Everything else can be compensated for. I speak from experience. I made the mistake once when building a garage. I was talked into doing the foundation myself and I thought that I had enough experience to do it, having worked construction. I learned that I didn't work construction long enough to do it alone. That is why there is more than one doctor in the operating room! /forums/images/graemlins/wink.gif

 

[EddieWalker]

Junkman just nailed it. If you mess it up, you're stuck with a disaster.

I can handle a broom finish 12 by 12 pad by myself, but that is my max. I've done enough this size to realize my limits. You also don't want to be just starting out on the learning curve on something so permanent.

In my part of Texas, finish house pads are $3 a foot right now. And that was a deal. Last spring it was $2.50 a foot. They set the forms, dig the footings, install and tie the rebar and when the mixer arrives, they get it were it needs to be and smoothed out. My latest pour was 44 yards and a full crew of 8 stayed until 8 pm working the power trowel getting it perfect. That was 13 hours of straight work on just the pour day.

They spent the day before setting the forms.

Another point, the first mixer got stuck is the loose soil. What are you going to do with a stuck mixer? They had 20 or more sheets of 3/4 inch plywood to lay down to provide traction.

Sometimes it's cheaper to have somebody else do it!