Pouring Concrete Over Concret?


Hi,
I have a old horse barn that has a floor that is part dirt (where the stables used to be) and part concrete. The problem it is not half and half, it is mixed and in places the concrete is cracked and broken.
I want a full slab in the barn to turn it into a shop. However, I don't want to go through the problem and costs of digging up all the existing concrete before I pour new. I am also wanting to put in radiant floor heating.
So is there any process that works for pouring new concrete over old concrete and having it still adher and be able to take weight of things like tools or even a car?
Thanks.
Alan
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Use some sort of latex adhesive as a bonding agent on top of the old slab and let sit for an hour or so before pouring the new slab.
Alan wrote:

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If it is cracked and broken, good chance the slab on top will crack and break in the same place for the same reason. Find and fix the problem first.
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wrote:

This is somewhat true, but some old concrete was poured way to thin. My old garage floor was apparently poured by someone that did not know how to use a shovel and rake. In some places it was 10 inches thick, in others it was only an inch. Of course the one inch parts were cracked. I no longer live there, but we poured a 4" slab right over it, and it held up fine for the 6 or 7 years we lived there.
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I would think that if you poured a full thickness 4 inch (or thicker) slab over the whole thing, it should not matter what is under it, as long as the old concrete is relatively solid. The problem is whether the different sections of concrete will allow for getting the whole floor level. If one section is 6 inches higher than the other, you may have problems. But if they are all about the same, just pour over all of it. That old concrete will just add to the strength of the floor, and you dont really need to adhere the new concrete to it, if you do a full thickness pour.
I'm no concrete expert, but I have poured some walks and a few garage and shed floors over the years., and I actually did pour one shed floor over and an existing shed slab, which was a smaller shed, so the old floor is only under part of the new one. In the new section I added some broken chunks of concrete under the new floor so I could get rid of them. The floor is solid and I never had any problems with it. I do not drive on it though, it's just a work shed and woodshed combo.
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Mike Ryan wrote:

Where is the project located?
If you're located where you need heat, I would suggest removing the old concrete & doing the whole this right.
W/o proper insulation you'll be heating the earth as well as the shop.
Might consider a wood stove or a gas fired blower.
How many sq ft of old concrete are we talking about 200? 500?
500 sq ft is only about 5 yds not a huge task to remove. IMO remove the old stuff it will be easier to work on a clean pallet rather than piecing the floor together.
How good do you want the new floor to be? How long do you want the new floor to last?
Any vehicle traffic on the new floor? HEAVY (1000's of #'s) machines?
How long was the horse barn a horse barn? Animal urine in the dirt can give new concrete problems.....investigate sulfate attack of concrete.
If you want the new floor to perform well you need a good base.
Do you have a concrete disposal (grinder) site near by? Your old floor can be your base material.
cheers Bob
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if your going to drive on it, then rip out all the old concrete and start over. otherwise its guaranteed to crack, plus you need a good base with all topsoil removed and several inches of gravel under everything and ideally a vapor barrier to keep out moisture. if your converting to a shop radiant floor heating is a good option.
a halfway patch job will long term just waste money
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rent a bobcat to do the heavy work, kinda fun and saves lots of back breaking work
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Having just completed a slab with radiant tubing in it, I HIGHLY recommend you remove all the old concrete and do it up properly. Since you won't be able to saw control into the slab, you'll want 1/2" rebar on 2' centers in both directions to minimize cracking. I would hesitate pouring the slab if freezing weather is in the forecast within 2 weeks of the pour. If you can get your radiant system up and running before the slab freezes, then all the better. No chance of heaving. Be sure to insulate under the rebar, and put the tubing on top of it. You'll need a flatwork crew familiar with the tubing process, and at least a 5" slab. This way they can still pull the rebar up near the center of the slab and still have ample concrete on top of the tubing.
--
Steve Barker


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Remove all the old concrete first.
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4" new concrete imbedded with 6x6-10-10 welded wire mesh. Concrete should be 3,500 or 4,000PSI.
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I would think that if you poured a full thickness 4 inch (or thicker) slab over the whole thing, it should not matter what is under it, as long as the old concrete is relatively solid. The problem is whether the different sections of concrete will allow for getting the whole floor level. If one section is 6 inches higher than the other, you may have problems. But if they are all about the same, just pour over all of it. That old concrete will just add to the strength of the floor, and you dont really need to adhere the new concrete to it, if you do a full thickness pour.
I'm no concrete expert, but I have poured some walks and a few garage and shed floors over the years., and I actually did pour one shed floor over and an existing shed slab, which was a smaller shed, so the old floor is only under part of the new one. In the new section I added some broken chunks of concrete under the new floor so I could get rid of them. The floor is solid and I never had any problems with it. I do not drive on it though, it's just a work shed and woodshed combo.
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some areas will sink under the weight of a vehicle and the entire thing will crack, espical;ly where existing concrete is
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