If you are a homeowner who has done any kind of renovations outside of your home, you know how time-consuming and difficult it can be. Most of us look for ways to cut corners and cut down on time, so we can get the project done quicker, such as pouring concrete over the grass for a project rather than clearing the vegetation first.
You should not pour concrete over the grass directly. For your concrete to harden flat and smooth, it is best to clear all vegetation and pour the concrete on top of smooth and debris-free soil.
Leaving grass under your concrete slab can cause some unnecessary issues for you in the future. In the remainder of this article, we’ll discuss these potential problems as well as best practices should you decide to pour concrete over the grass.
Why You Should Not Pour Concrete Over Grass
When you are pouring concrete, you want to make sure the area you are preparing is flat, and the soil is free of debris. Making sure the earth is compact and strong is very important.
Grass Regrowth Leads to Cracking
When you prepare to pour a concrete slab over a previously grassy area, you want to start by digging down into the soil at least a few inches. Not only do you want to remove the visible grass blades, but you want to get down under the roots to prevent any regrowth.
Leaving any roots to grass or weeds can lead to regrowth up through the concrete cracks. Although grass is likely not going to be strong enough to crack the concrete itself, it can find little microscopic cracks already formed and push its way through, creating a larger, more noticeable split.
You Will Have an Uneven Foundation
If you try to pour concrete over grass without creating a sturdy foundation, you are guaranteed to find issues pretty quickly after it dries.
Once your concrete starts to dry, it will settle, pushing its weight down into the earth. If the area you are pouring concrete in is not even all the way around, the concrete will not be either. You will end up with a slanted slab or cracks where the pressure was too much for the slab to hold. If using this concrete for a hot tub, and its uneven, don’t worry there is still a way you can make it work.
Concrete Requires a Gravel or Sand Base
You must lay a base of sand or gravel down before you pour your concrete. Changing weather does not affect sand or gravel, meaning the base will not expand or contract when the temperature changes, therefore, reducing the risk of cracking in your concrete slab. If the grass is used in place of this layer, your base is more likely to shift over time.
Note: This is not necessary if your natural soil already has a lot of gravel or sand mixed in with the dirt. Simply clearing some areas of grass completely will leave the ground ready for the concrete to be poured.
Is Pouring Concrete on Grass Ever Okay?
There are no guarantees when pouring concrete over grass. When a root is alive, it is bound to continue searching for a way up no matter the obstacles in its path. But if you are in a hurry or just don’t want the hassle of removing all that ground, there are a few situations you may be able to get away with leaving the grass where it is:
- If you pour more than 6 inches: A very thick layer of concrete may not prevent grass from growing up through your concrete pad but will take more time to work its way through.
- If it’s temporary: If you plan on removing the concrete from its spot within a year or two, pouring it on the grass is not going to be an issue. It will still form, harden, and keep its strength.
- If you do not mind maintaining the concrete: In these cases, feel free to pour over the grass. Filling cracks and gaps can be a DIY project and relatively inexpensive.
- If cracks and uneven surface isn’t an issue: If you are pouring concrete as a base to hold up smaller items like air conditioners, outdoor utilities, or even around your mailbox, smaller cracks and a slight tilt may not be a problem for you.
How to Directly Pour Concrete Over Grass
If you do end up pouring concrete on your grass, it’s essential that you follow the proper procedures to ensure you experience fewer issues with your new slab later.
Make sure you know where you are going to pour your concrete before you start. Although you may have a great idea in mind, without measurements and visual details, you may not like the results. You’ll also want to make sure you have the right concrete mix for your project.
Best Concrete for Pouring Over Grass
When selecting the best concrete to pour over grass, you want the ones geared towards outdoor use. The best choice for that is a quick-dry concrete that only requires water before pouring. You’ll also want to look for concrete with the following features:
- Dries within 24 hours: This prevents the risk of accidental footprints (or paw-prints) drying in your pad. It also keeps the pour safe from unpredictable weather like rain or windstorms.
- Easy to use: Most quick-drying concrete should only need to be mixed with water; you don’t want anything that requires many steps. This is to prevent any errors that can result in ruining a large amount of concrete mix.
- High-quality concrete mix: You want the concrete mix to be a good mix of rocks, sand, water, and concrete (water and concrete create the “paste”). The best combination will have a high content of small rocks and a lower content of concrete, around 15%.
The following brands are known to have these grass-friendly features:
- Quikrete: This concrete is easy to use, highly durable, and hardens within 24 hours.
- Sakrete: This is a budget-friendly, professional-grade quick setting concrete formula, ready for foot traffic within 6 hours.
- MasterCraft: This concrete dries 90% faster than other concrete mixes and is available for very affordable price. This product is a high strength concrete perfect for your backyard projects.
Till the Existing Grass
Till the existing grass the entire length of your walkway or to fit the size of your project. Be sure to till the grass from the roots and shred them completely, so there is no chance of them growing back.
Pour Your Concrete
It is imperative that you mix and pour the concrete correctly:
- Mix the dry concrete with water, saturating the entire mixture thoroughly.
- Next, you want to board off the areas you want to add concrete with wooden planks, so you have a perfectly edged section.
- Pour the concrete into the wooden boards, being careful not to allow the mixture to overflow or move the location of the boards. Ensure you are completely covering the area of grass and soil you want the slab to be placed.
- Create a few inches of depth to ensure your concrete will not crack under pressure.
- Allow plenty of time to dry before removing the boards around it.
Tip: If the area around the pad seems a little uneven or slanted, add decorative stones or mulch around the edges. This will disguise the faults and create a beautiful look.
Although certain projects allow a little wiggle room by leaving grass underneath your concrete, it is best to remove all grass and loose debris before pouring. This will ensure you have an even, smooth, crack-free look for many years without needing to deal with any expensive or time-consuming maintenance. Be sure to check are article on how much concrete you need for a fence project.