Preparing site for concrete pad???

[RedDog]

One of the dumbest things I did was not having a pad poured in front of the garage when the house was being built. /forums/images/graemlins/mad.gif

Now it is time for the pad. /forums/images/graemlins/smile.gif

I have never delt with concrete before, or the preparing of the site. Should the pad drop about an inch so water does not run into the garage? Should the pad be level, or slope slightly to allow the water to run off? The pad will be about the width of the garage, and 20 feet out. Photo is attached.

When preparing the site, should you use gravel, sand, or dirt to fill in some of the low spots? I have worked on it somewhat with my tractor and have a few low spots that need a little fill before the concrete. I would like to fill them and then run the tractor over the entire area a few times to "pack" the surface before the concrete.

Any help appreciated,,,,, RedDog <font color="orange"> Kioti DK65 </font>

 

[shado]

Yeah, it should slope down just a bit to help keep water from building up against the doors, I'm sure your'e shooting the site with a transit to help with these measurements. Gravel should be used to help level, if you use sand, it could possibly wash away some if it rained before you got the cement poured. Ants could also create cavitys beneath the slab at a later date (remember those ant farms?). And I know it's not really necessary since a vapor barrier is not needed for outside, but I would lay down a layer of plastic just so the concrete won't soak through to the rocks before it cures, you might have a deep area of rocks & the concrete might have more cavity area to fill in, thus maybe creating 'low spots' in the pad.
J.W.

 

[Slippy]

I am by no means an expert, but have preped site for my pole barn and patio. First, I determine how thick the pad will be, which will determine the top of your preped finish grade. I had mine 4" thick. I would also dig footers 18" in diam. below the frost line. For me that is 32". Next, I have used crushed rock w/lime stone to pack in good and tight. What I have used is almost like dust. It is a left over product that is really cheap. Don't remember what it is called, but I used my 4 wheeler and pulled my yard roller over it over and over again until packed real tight. I then had floor put in. My pole barn floor is the only floor that has not cracked.
Like I said, I'm not an expert and I could be doing it all wrong, but it worked for me.

 

[EddieWalker]

I'm not a concrete expert, but I've done a few driveways and even more sheds.

In my area freezing weather isn't a major problem, but unstable soil is.

To minimize movement of the pad you need a good base. Everything comes down to foundation. We use a couple of inches of limestone and pack it with a vibratory plate, 5ph. Just keep running it for the full 4 hour rental time is enough. You will never get compaction just running over fill with a tractor or truck.

If you are using the driveway for residential vehicles and nothing of excessive weight, then standard framing 2X4 are fine for your framing. Use 3/8 rebar around the edges within an inch or two of the framing then build a grid with the rebar every 16 inches. I use plastic posts to keep the rebar at the right height, but on small pads rocks work also. I've also used little cement blocks from Home Depot. Just make sure the rebar is off the ground. Also be sure to check for the height with your scree board in order to be sure the rebar and wire doesn't come above the finish level of the pour.

I did a driveway two weeks ago and the next day received 2 3/4 inches of rain in one hour. Nothing came into the garage. I determined where I wanted the water to run off when setting my forms, which will vary from location. I want the water low spot to be at least 8 feet away from the garage door.

I use a 6 foot level and tape a piece of wood 1 1/2 inch thick to the end and use this to determing my slope. Nothing is written in stone here, and you can eyeball it some also, but double check with a level to be 100 percent sure you know where the water is going.

Get some friends, tools and hope for a nice cool day.

 

[Anonymous Poster]

The pad should drop as you say. You need to use a gravel/sand mix for the base or some commercial base.

I'm not sure that running your tractor over the site will provide the correct compaction required you should use a tamp either manual or gas powered you can rent them at most rental places.

You also need to figure on putting wire mesh in the slab since you'll be driving over it. It should also be a minimum of 4" thick unless you have something very heavy running on it.

You should also consider a tapered footing around the edges and additional reinforcement wire/bar to defray stress cracks.

 

[Anonymous Poster]

I always want to put a slope on a pad, so I can control where the water will go. If you don't control where it's going, it's probably going where you don't want it. Murphy Rules. Minimum slope on concrete is about 1/2 percent, but I'd double that if you're not confident about being able to screed it out flat. In the end, like most projects, you'll take what you can get for slope.

You can improve your screeding accuracy by forming strips and pouring every other strip. Then strip your forms and pour the intervening strips. This keeps your screed lengths manageable.

A good base is important. I like well graded stone - whatever your state highway department uses for road base. It compacts well. Compact it with a vibrator plate. A 6" base is usually about right. More base won't help you much, unless you need it to make up for sins in your grading.

I'd probably go with a 6-inch slab for most vehicle loads. In reality, your formwork is likely to be store-bought lumber, so you're talking 3-1/2" or 5-1/2 or 7-1/2" inches. The former is a little thin for my blood. I usually call for 7 to 8 inch slabs for semis, depending on the underlying soil. The thickened edge is a nice detail, if you can grade out the base adequately. The edges of a slab are the weakest part. I'd go with an extra inch for about 1/3 of a panel width. Taper the joint between the thick and thin.

Contrary to popular impresion, reinforcement does not do much to strengthen a slab against traffic loads. It does help with shrinkage cracking. If you're going to use steel, I'd use wire mesh panels. Lay them on the ground and hook them up as you pour. You want the steel in the bottom 1/3 of the slab. If you lay them on chairs, you still have to hook them, as the concrete will probably push the wire down.

Concrete shrinks. When it shrinks, it cracks. Contraction joints help control where it cracks. (If you can't prevent it, make it look deliberate.) Since you don't want to saw the slab, I'd tool the joints. Joint spacing should be 24 X the thickness, or two feet per inch.

Do get a good cure. Visqueen the surface, water it, and try to keep it wet for as long as you can - about a week. You can also get spray applied curing agents that hold the water in. They're a waxy kind of product. Try to pour in cool weather.

Use air entrained concrete, if it freezes in your area. Your readi mixer can give you 6% air for only a small premium. Don't let the trucker water down the mix as he pours. That will weaken it over what you bought from the yard. It will work fine, as delivered from the yard, if you work it a bit. I'd rent a vibrator. That moves the concrete around well, but don't over vibrate.

- Dennis

 

[dougtrr2]

Where the two slabs meet I would go for 1/2" drop or less. The apron outside my garage settled over the years. When the difference got to 3/4" or the bump driving in got quite annoying. Since your area looks relatively level, I would probably go with a flush fit and a slope away from your garage.

Doug in SW IA