Can You pour new concrete over old concrete?

You could, but it's certainly not recommended. Any cracks in the existing porch will continue to move and put pressure on the bottom side of your new concrete and crack it in the same exact places.

If the old porch has to stay another option is concrete overlay. This is done by some decorative concrete companies. For more info go to: www.concretenetwork.com

Years ago we bought a house with a patio in back, and the patio had sunk in the middle and broke the potio with a break that water had gotten into and then the cold winters had broken the pipes that were encased in the cement that had both electric lines and water lines within the cement. It was a mess but was a mess because someone decided to put new concrete over the old concrete and it made the patio so heavy that it sunk in the middle and so they added more concrete in the middle to try to even it out and that didn't work either.

So my suggestion to you would be that if you're unhappy with your present concrete porch that you have a couple of guys rent a machine or two that breaks up concrete, have them spend a day and break up the concrete, and then hire a truck to come remove the old concrete and take it to the dump....and then start all over with a porch that you'd like better. Perhaps you'd rather choose a wood flooring on the porch and then screen it in.

I agree with Don, but if you must overlay you'll need a minimal thickness of about 2". Thoroughly clean the existing concrete and apply a product that bonds the new concrete to the old. If possible, however, remove the old and make sure there is a solid substrate for the new concrete to rest upon that has a 4 inch thick layer of cushion sand.

I would scrub the old concrete with a muratic acid wash first (using the normal safety precautions) and use concrete bonder in the new mix. Still risky but this will give it your best chance of a good bond. At Home Depot/Lowes you can find a bagged concrete mix formulated for surface bonding if it is a relatively small area.

Yes. Use a minimum of one and half inches thick new concrete over stable existing concrete. If the reason you are doing this is because the old slab is breaking up, you need to have a professional to look at it to determine if old slab pieces need to be removed and if you have enough head room, whether it will interfer with doors, etc. Wish you would of added why you are considering it and condition of existing. Post back with more info, please.

Yes. you need to make the surface of the current floor rough so the new floor will expand and contract at the same rate. Best to remove the old, but if you are going to put at least 3" thick of new concrete, you can put it on top. Must be at least 3"

Yes as long as the surface is prepared right. There is a resurfacer concrete that is used.

Yes, but you need to prep the area with a pva primer, you can get it in the cement department at Lowes, it comes ina jug and is a blue white color, you paint it on the old service witha brush.

You can also consider tile, or deck boards held in place with construction glue

you can but it likely will not bond to the old cement