Can You Pour Over Existing Concrete?
Updated: Mar 11, 2022
Concrete, no matter where you have it in your home, is durable and long lasting. However, when it does come time to replace your concrete - be it your driveway or backyard patio - there are a few steps to keep in mind.
First, know that you can absolutely pour new concrete over existing concrete. It is not completely necessary to break up and haul away all of your existing concrete in order to pour new concrete. But you want your new concrete to look good, right? You want it to last for years to come with little maintenance, don’t you? To do that, there are some steps that need to be completed first.
Steps before you pour
Before you can pour new concrete over existing concrete you need to know if the existing concrete is structurally sound. There are two main things to look for to decide if the existing structure is sound - settling and heaving. Does the concrete structure look like it has settled? If so, has it settled uniformly throughout the slab? Does it appear that it could settle more?
If the concrete looks like it is heaved in any area, look to see the reason why it has heaved. Are there tree roots running under the slab? Did the slab return to its original level after it heaved or did it remain heaved?
If a slab has yet to fully settle or it continually heaves, it is probably not a good idea to pour new concrete over the existing concrete. How your current concrete looks and responds to the conditions around it will directly determine how the new concrete will look.
Just like patching a crack in your wall that keeps coming back, pouring new concrete over a slab that is not structurally sound will not magically make your surface look new again. Until you address the issues at the base of the problem, the concrete will continually have cracks or heave.
If you are able to pour over existing concrete - great! This means you have a solid base and just need a fresh updated look. Before you pour, it is a good idea to thoroughly wash the existing concrete. Using a pressure washer is ideal for this as it can easily remove all the dirt and mold that may have built up on the surface over the years. Then let the concrete fully dry before adding a bonding agent to help glue the two concrete slabs together.
Don’t pour too thin
When pouring new concrete over existing concrete, you may think you only need a thin layer of new concrete to cover up all the imperfections of the old concrete. Unfortunately that is not the case.
Concrete is made up of rocks, the smallest of them being ⅜ of an inch thick. You want to ensure that your new concrete properly adheres to the existing concrete. If you don’t have enough concrete paste over the top and around the current aggregate, you will not create a strong base. This will cause the new concrete to break or flake off easily, leaving you right back where you started.
New concrete should be at least 1.5 inches over the existing concrete. That is the minimum. Ideally, new concrete should be at least two inches on top of the existing concrete for the strongest, more durable hold and the longest lasting wear.
It is a good idea to seal the new layer of concrete once it has fully set. This will help to reduce cracks forming. If a crack does form, repair it quickly.
Existing concrete slabs that work best to pour new concrete over are driveways, basketball courts and patios. Just be sure to completely check the condition of the ground beneath the concrete before pouring new over. Cracks and heaves in your existing concrete will carry over to the new concrete if they are not properly addressed.
When you have to start fresh
Unfortunately, not all concrete can be poured over with new concrete. Sometimes you have to bite the bullet, tear out the existing concrete and start fresh. While it would be easier to not have to do that, knowing this ahead of time, will save a lot of frustration (and money) down the road.
Concrete slabs that are spiderwebbed with cracks, sunken in areas and heaved in others are a sure sign that the slab needs to be completely replaced. Obviously there is something going on under the concrete that is causing all these issues. If you don't address it, it will keep ruining your concrete - which should last you up to 40 years.
The base under the concrete should be solid and firm. Tree roots and uneven soil - even in the slightest way - can cause massive damage to the concrete. The freezing and thawing in colder climates (like Michigan) will cause uneven surfaces to heave in the cold months, when water freezes and then thaw and sink in the warmer months when the ice melts. In our state, we deal with enough potholes on the road, we don’t want to deal with issues like these at our home!
Tree roots will also wreak havoc on your concrete if they are not removed or redirected. A tree wants to live and when it grows it grows both vertically into the air and horizontally beneath the ground. Roots will snake underneath concrete and depending how close they are to the surface, can cause cracks, heave the concrete or even poke through.
The bottom line is, make sure you have a firm solid base free of all debris before pouring your concrete. Doing the extra work in the beginning will help to create a concrete slab that will look and perform beautifully for decades to come.
Other areas where it is better to replace, rather than pour over existing concrete are staircases or anywhere there is a doorway.
Staircases require precise rises and slopes to ensure safety. Pouring new concrete over them would change both dramatically and make for bulky and unsafe stairs. Doorways are also an area you need to be careful about when considering pouring new concrete over old. Adding an inch and half to two inches of new concrete would make it difficult to open or close existing doors and make the transition from one floor to the other potentially dangerous and at the very least a trip hazard.
The bottom line is yes, you can absolutely pour new concrete over existing concrete. But don’t rush into it. Take the time to examine your existing concrete, how it performs in the summer and winter months and make sure that if you do pour over top of it, you will not be dealing with the same issues five or 10 years down the road.
Concrete is designed to last. If you take the time and proper steps before pouring, it will wear well and look beautiful for many years to come.