Question for Concrete Experts

[73survivor]

I have a 12 x 24 garage that the concrete floor slopes to one side and I would like to put a drain in the middle of the floor so I can wash cars in the winter. I want to pour a new floor so the water runs to the middle. This is my question: Can I pour 4" of concrete on top of the existing slab without putting any stone down first? Do I need to tie in with the existing slab with rebar? Ceiling height is not an issue and I don't really want to dig the existing floor up, just pour on top of it. Any suggestions are welcome. Thanks

 

[bmwpower]

If it were me, I would pull out the old floor and then pour the new one.

If you're going to pour on top, how are you going to deal with the garage door height? The door is not going to seal properly if it's now 4" higher off the floor.

Anyway, no stone will be needed if you pour on top. What is the condition of the current slab? Any cracks, etc.? The new floor should be fine if the old floor is stable. I would tie the new floor into the old floor using rebar. Put in several control joints, preferably in the same locations as the original floor.

 

[mike944]

You'll probably have to do the project "under the radar" of your local building inspector. Most won't let you put in a floor drain. They say too much environmental risk of motor oil, antifreeze, etc... getting into the ground.

Around here, i've even heard stories about the inspector wants to be there when the first cement truck shows up, specifically to make sure you haven't added a drain since the crushed base, and mesh was inspected.

That being said, i think a floor drain would be fantastic to have, specifically for the reason you listed.

As to your original question, i'm not a concrete expert, but i think the right way to do this is to pull up the old slab. if it's cracked, or settles under the weight of the new pour, it could easily crack your new floor.

If you decide to pour over the old slab, i would put extra mesh in place. One in the normal place near the bottom of the slab, but a second piece near the top to handle bending loads in the other direction as well. this should help reduce the likelyhood of cracking.

 

[73survivor]

If it were me, I would pull out the old floor and then pour the new one.

If you're going to pour on top, how are you going to deal with the garage door height? The door is not going to seal properly if it's now 4" higher off the floor.

Anyway, no stone will be needed if you pour on top. What is the condition of the current slab? Any cracks, etc.? The new floor should be fine if the old floor is stable. I would tie the new floor into the old floor using rebar. Put in several control joints, preferably in the same locations as the original floor.

I don't presently have a door on. The opening is 8' high. I was waiting until I got the floor done and then order a door for the opening. Some small hairline cracks. How far apart for the rebar to tie it in?