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Can You Pour Concrete Over Grass?

Deciding on new landscaping ideas for your property is always fun and exciting, but it also comes with more planning, and little bumps in the road along the way than most probably wish for. 

Unfortunately, most of the time, it isn’t as simple as just deciding on an idea and executing it on the same day—there’s a lot more that goes into carrying out a cool new landscaping project. 

For example, if you want to add or expand a concrete area on your property where there’s currently grass, it isn’t as easy as just simply pouring the concrete on top of it. In this article, we’ll go over the proper way to go about that scenario to ensure that your yard renovations go as smoothly as possible.

What Happens If You Pour Concrete Over Grass?

It’s intriguing to want to cut corners where you can, but sometimes it’s worth it to just put in the extra time and effort so that you can be certain you’re ending up with the best end result possible. 

If you pour concrete over grass, everything may seem to have worked out just fine at first, however as time goes on, there could be some premature cracking in your new concrete. 

Grass regrowth is likely to cause an unevenness in the ground beneath your concrete, which is likely to lead to unwanted cracking far before you’d expect it. 

So while you technically can pour concrete over grass and have it set properly initially, it’s a good idea to ask yourself if that’s something you should be doing. 

In the long run, if you cut the corner of not removing the vegetation from the soil before pouring concrete, you’re only going to end up wasting more time and money. So while it may seem like a good time-saving idea, pouring concrete directly on top of grass will very likely be something you end up regretting.

Reasons Why You Should Not Pour Concrete On Grass

When you pour concrete over grass, the chances of said concrete cracking or drying unevenly drastically rise. It’s best to pour concrete over a flat, compact, and vegetative-free surface, which will help ensure that it dries and hardens in the way it was intended to. 

Since concrete requires an even foundation to properly set, pouring it over grass will mean that it’ll settle unevenly, leaving you with slanted slabs and cracks where there was too much pressure for it to hold. If the area that you pour your concrete isn’t even everywhere, then your concrete won’t be either.

On top of that, grass regrowth can also pose a risk to your newly poured concrete. Even though it won’t be strong enough to crack the concrete by itself, it can grow up through tiny, already formed cracks and make them more noticeable. Avoiding this problem is in both your and your concretes best interests.

It’s a general rule that concrete only gets poured over sand or gravel, as these substrates don’t contract or expand when the temperature changes. 

This is an important factor since if the ground beneath concrete expands or contracts too much, cracks will start to form. Using grass as a base layer instead of gravel or sand will increase the chances of the growing shifting, therefore increasing the chances of cracks happening.

How To Pour Concrete Over an Area That Currently Has Grass

While we’ve established that it’s almost never a good idea to pour concrete directly over grass if you’re still considering it, here are a few tips and tricks to help make sure you end up with the best end result possible.

  1. If You Pour More Than 6 Inches of Concrete 

While this won’t really help prevent cracking, pouring a very thick layer of concrete will mean that it’ll take longer for grass to work its way through the cracks. 

If the grass is still alive, it’ll always do everything in its power to continue growing and thriving, which is why you’ll often see it growing in impossible-seeming nooks and crannies. A thick layer of concrete may not stop this entirely, but it will for sure delay it.

2. If the Concrete is Only Temporary 

If you’re planning on removing the concrete within a year or two, pouring it directly on top of grass may not be a huge issue. If it sets properly and doesn’t crack right from the get-go, it should hold its strength for a couple of years.

3. If Uneven Surface and Cracks Aren’t an Issue For You

If you don’t mind that the surface of your concrete doesn’t look the best or prettiest, you might not have a problem with pouring it over grass. For example, if you’re using it as a base for holding up smaller items and not for recreational use, the way it looks might not matter so much to you.

4. If You Don’t Mind Maintaining the Concrete

If, for whatever reason, you’d prefer to just fix the problems of cracking as they arise, pouring concrete over your grass may not be an issue. Filling in the cracks will be relatively easy and cheap, so it won’t be the biggest hassle to do it this way.

Next Steps

Now that we’ve discussed a few precursors to pouring concrete over grass, it’s time to go over the actual process of doing so. Like any time you pour concrete, you’ll want to plan ahead with both the measurements and the type of concrete you’ll be using. 

The process of pouring concrete over grass isn’t much different than if the grass weren’t there; you may just want to consider a kind that’s better suited to having vegetation below it. 

Concrete that’s geared toward outdoor use and that dries within 24 hours is your best bet. Along with that, choosing a high-quality, easy-to-use mix will help ensure that you get the best results possible. 

These are, of course, helpful steps to take even when pouring concrete with no grass below, but since you’re in a position of having a higher chance of cracks and unevenness when pouring over grass, you’ll want to take as many possible precautions beforehand.

Will Concrete Kill Grass?

Since concrete will smother and block any light from reaching the grass, yes, the vast majority of it will die. The only exceptions are the blades of grass that live below any cracks that have formed since some water and light will still be able to reach them. 

Grass is incredibly resilient and will manage to thrive in even the most dire conditions, and a crack in the pavement is no exception. Although other than these few stragglers, grass that gets covered by concrete isn’t likely to live.

Conclusion

For the small amount of time and effort it takes to remove grass, it’s almost always worth it to do so before pouring any concrete down. You’ll end up with a better end result, and in the long run, a lot fewer cracks. 

So even though you technically can pour concrete over grass, it’s still a good idea to reevaluate—taking the time to remove the grass will leave you with many more years of pristine, flaw-free concrete.

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