I agree with all above you should get rid of the old “slab.” There are a couple easy tricks to make it an inexpensive, easy and durable pour you can do with armatures.
Remove the old, form the new. 3” minimum. Of course level the bottom. Now here’s the trick. Dig the two long sides about 3” deeper about 6” wide, so you end up with two long integrated “beams” for the sides. Put a 4“ rebar in about 1.5-2” clear under the bottom so there is 60% concrete above and 30% below. You can hold it off the bottom with a rock, but make sure it’s a very clean rock, not covered with dirt or clay, that will bond to the concrete. Where ever you have to splice, over lap the rebar at least 18” and triple wire it tight.
Second trick is pour a tic-tac-toe board instead of a slab. Not necessarily 3 rows, can be two, but groove a control joint every 4-5’. Contrary to the side deeper beams, wherever there will be a control joint, about 2” wide, build up a little rise on the base. You can do this by putting a cheap 1/2” or 3/4” pvc pipe across and down the middle, laying on the bottom. The point/purpose is the concrete WILL CRACK, so you pre-arrange for it to crack at the joints grooved above the pvc.
Next trick is the “mix.” Most driveways in the south are 2,500 psi mix. Its usually a “slop” run from the plant with very little control. It’s only a little bit more expensive to get a 3,000 or 4,000 mix. Next trick, when you order it, tell them it’s for a “structural” slab and it’ll be “slump tested” on site. Then I wouldn’t do that, but they don’t know that, and they will be much more careful how they put the mix together in the plant and control the delivery time.
The next trick is to order “fiber-crete” which is simply dumping a bag of fiberglass strands into every yard of concrete at the pour site and mixing it in on the truck. I don’t remember the exact mix (bag per yard?), but this is also fairly inexpensive, AND, if you use fiber-crete above 3000 psi and you keep your control joints no more than about 5 feet, there is no need to put wire in the slab-a lot less work and easier to do.
if you order it that way, it’ll come in pretty stiff and hard to work, but you can add some water when putting in the fibers and loosen it up for easier working. Don’t soup it up too much.
Then it comes down to technique and features. Make sure the sides are level, not necessarily level to gravity, but carefully placed for whatever slope you want. Down the middle of the slab, put in some 1” x 1” stakes at the right elevation to control the slab level. Obviously you want it to crown in the middle and drain to the sides, or you want it to drain from one side to the other. As you’re pouring the concrete and you get the right finish level around the stakes, just take a hammer and pound them down below the surface at least an inch and then finish that spot.
Afterthought, but I would do the “beam” concept across the beginning and across the end as well. Cross the rebar at least 2” and cross tie it tight.
And finally, I would run a 1 1/2 inch PVC pipe/conduit underneath everything from one side to the other side about every 15 feet, let it stick out past the slab a foot or 18 inches, and cap it no glue and bury it, but make sure you map out where they are. Take a penny and put it over the conduit on each side, work it in but the top surface exposed. When the concrete sets, polish it off & you’ll always know where the conduit lies. Then when you build out the TRS Guest Center, it will be very easy to run electric, low-voltage lights, a waterline, whatever wherever.
Finish it flat and smooth, trowel it enough to bring the slurry over the sand and rock like spackling paste/wallboard finish. 30 minutes after the concrete gets hard, lightly drag a hair broom across it to create texture. Don’t broom it hard enough to sweep anything, just enough to draw lines from the hairs across it.
Don’t take off the forms for two days, and have a couple bags of mortar mix ready, so when you do take off the forms, if there are any hollows, mix up the mortar mix and immediately push it in wet and put a board in front of it again for a day.
And, one of the most critical steps most amateurs skip. After three weeks or four weeks, not before, wash it off with a hose, let it dry, and then put a good quality concrete sealer on top of it. Concrete, no matter how strong, is basically porous. If you don’t seal it, water will get in, freeze, and crack the concrete or pop off the finish. You can avoid this by sealing it after it’s fully cured, about 30 days, and then do it again every 7 to 10 years.
My driveway out front was poured this way and it never even chipped from 1998 to now until AT&T (Satan spelled backwards) set up a 16,000 pound boom truck to work on the telephone pole on it. I’m still in a lawsuit about that…
Yeah, yeah, I know take the keyboard away from Rick W, but I hope this helps....
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