The short answer is yes you can pour new concrete on top of old concrete. However, there are several things you need to have in mind before you do so.
For instance, you must think about the structural soundness of the old concrete before putting anything new on it. So how do you know if the old concrete driveway is structurally sound?
Well, you look for settling first. If your old concrete slabs are settled, ask yourself why. And also ask yourself if the slabs are truly settled and whether they can still move a bit more. If the settling is final and somewhat even among all the slabs that make your driveway, you can add new concrete over the old concrete because it shows the old concrete is stable and will form a good base.
Secondly, you need to look at the condition of your old concrete slab driveway. If there are cracks all over it, you cannot pour new concrete over it. Because cracks mean an unstable ground underneath and new concrete is not the solution to that.
However, if your concrete driveway is solid and only has minor cracks or looks not so great, you do not have to even think a lot about it. You can simply mix and pour concrete on top of it.
What is the recommended thickness of a new concrete driveway over old concrete?
There is no recommended thickness. There is only the minimum thickness. When pouring concrete, you must make sure the new concrete is at least 1.5 inches. The reason why this is important is that the smallest rock in the concrete will be about 3/8 inches. If you add concrete that is less than 1.5 inches, there will not be enough cement between the aggregates to make the new concrete a strong concrete. The new concrete will not last long. It will start cracking and this will eventually lead to breaking. So never add concrete less than 1.5 inches thick.
How to pour new concrete over old concrete
- Thoroughly clean your old concrete. This is important because you do not want dirt, loose concrete, mold, and grease on your old concrete affecting your new concrete. So clean your old concrete thoroughly using a pressure washer.
- Let the concrete dry for at least a full day. This is important because water or moisture is going to affect the effectiveness of the chemical bonding agent you need to apply next.
- Apply a high-quality concrete bonding agent. After the old concrete dries completely, apply a light coating of a high-quality concrete bonding agent. It is what will bond concrete slabs tightly together.
- Use a machine such as Topcon RL-H5B for grading. This is important whether you want a level base or a base with a certain slope. If you do not know how to use a grading machine, maybe you should consider consulting a professional. However, the Topcon machine I have mentioned above is quite easy to use and it should not prove to be any difficult for you to use.
- After you have set the forms during grading, you should install the wire mesh. After this, you simply need to request concrete from a ready-mix supplier. No need to make the concrete mix yourself. If you want a concrete mix that is going to be easier to stamp, get the one with the 3/8 inch little rocks instead of the one with the ¾ inch little rocks.
The 3/8 stone mix is not only easy to stamp but also easy to use to create a broom finish.
- Pour the concrete and then level it. After pouring and leveling, let the concrete set to the point where it is ready to stamp and then stamp it.
- After stamping, add color if you want. Make sure you use a cement or concrete color to paint your concrete driveway. If you use anything else, it may not look nice and it will quickly be made to look old by the weather.
Can you lay new concrete on old painted concrete?
You can definitely do this especially if the new concrete is going to be at least three inches thick. This is because if the new concrete is not more than three inches thick, it will not stick very well to the old painted concrete.
In case, you want to pour concrete that is not more than three inches thick on a painted concrete driveway, you have to remove the paint first. You can do this by grinding off the old paint or using a hot water pressure washer.
After removing the old paint, you have to apply a concrete bonding agent to bond or glue together your old driveway concrete with the new one.
If your new concrete is more than three inches thick, instead of applying a bonding agent, you should apply a bond-breaking agent. This will enable the independent expansion and contraction of concrete slabs and prevent their cracking and breaking.
Does new concrete stick to old and dried concrete?
Yes, it will. However, to make the bond between old and new concrete very strong you need to use a concrete bonding agent. One of the best concrete bonding agents is Weld Crete. It is kind of like Gorilla Glue but for concrete. It is particularly important to use a concrete bonding agent when the new concrete is less than 2 inches thick because it is more difficult for such concrete to binding to old concrete.
If you do not want to use a concrete bonding agent at all, you should grind your old concrete thoroughly to make it more likely to it stick to new concrete.