Cracks in concrete patios, driveways and pathways can be unsightly – and will also become larger and attract weeds if left untreated. So what can you use to fill concrete cracks and how do you go about it?
To fill narrow cracks in concrete that are ⅛ of an inch wide or less, use an epoxy compound or a latex-based formulation to seal each crack. For larger cracks or chipped concrete edges, mortar mixes are the best option as they both fill and seal the cracks.
Let’s dive down into the subject of filling concrete cracks in more detail, and discover some different products you can use to get the job done, plus a process to follow to get it done right…
What Can I Use To Fill in Cement Cracks?
Cement cracks are reasonably easy to repair. Cracks are inevitable in concrete eventually, so it’s worth learning how to deal with them. You can buy concrete repair mixes online, from websites like Amazon, in your local hardware store, or from home stores like Home Depot and Lowe’s.
Different sized cracks need different approaches. For narrow cracks (by narrow we mean cracks that are about ⅛ of an inch wide or less), use something like an epoxy compound, or maybe a latex-based formulation. These are smoothed on with a putty knife or mason’s trowel, or come in bottles with nozzles for easy application into narrow cracks.
If you’re dealing with a larger crack or chipped concrete edges, mortar mixes are the best option. You can buy ready-made mortar mixes from hardware stores. If you want to make your own, the basic mix is one part Portland cement and three parts masonry sand, which you mix with fresh water to form a paste-like texture.
It’s also worth bearing in mind that there are essentially two approaches going on. Smaller cracks tend to be sealed, which prevents them expanding and protects the concrete from further damage. The mix approach involves actually pushing the formulation right down into the crack, so it’s being filled and repaired as well as sealed.
What is The Best Concrete Crack Sealant?
There are lots of great concrete crack sealants and mixes available. Which is the best depends on what sort of cracks you’re dealing with, and how highly you rate “easy to use” as a decision-making factor. As we discussed earlier, smaller cracks can be easily sealed with a more caulking approach, while deeper cracks are filled with a mortar mix.
We took a look at a selection of popular concrete repair products, and chose a few that had good reviews on Amazon. There’s plenty of choice for both the main types of cracks, so the main thing you need to know is what size gap you’re dealing with.
A really easy way to cover cracks and prevent them becoming worse is to use a concrete crack sealant like Bluestar Flexible Concrete Crack Filler. This comes in a bottle with a nozzle, and it’s as easy as squeezing the ketchup along your hot dog (pretty similar action, too).The gray-colored filler seals cracks of up to one inch wide to prevent further damage, and flexes to manage changes in temperature.
For a ready-made paste, Sika’s Sikacryl Ready-Mix Concrete Patch Repair is an acrylic latex based mix that you push into the crack with a mason’s trowel. The Ready-Mixed Concrete Patch from Dap gets good reviews. It’s great for cracks on driveways, and dries to a durable and solid finish. Dap also makes a concrete sealant, which is great for quick repairs as it dries in three hours.
For the best of both worlds, Red Devil makes a patch repair that comes in a tube. This saves time and mess, and is so easy to apply. Just be aware that it’s not suitable for driveways or garages, only places with no vehicular traffic.
If it’s strength you’re after, go for the kit from Rust-Oleum (yes, the grill paint people). Their two-part epoxy filler is actually stronger than concrete. This industrial-strength product repairs holes as well as cracks, won’t shrink or crack, and is ready for painting (should you wish to) in an incredible eight hours.
How Do You Fill & Repair Gaps in Concrete?
Filling gaps in concrete is a straightforward job, and once you’ve done it once, you’ll wonder why you put it off.
This is how you repair a crack in the concrete using a ready-mixed mortar, like the ones from Amazon that we mentioned earlier.
- Clean the area thoroughly, making sure it’s free from particles like dust and dirt (don’t pick a windy day for this reason!). The ground also needs to be dry
- Using something like a mason’s trowel, push the paste into the crack, ensuring it gets right in (that’s why the paste method doesn’t work as well for hairline cracks)
- Press it in firmly to avoid any air gaps. You may want to use a putty knife for this
- Smooth the surface to the same level as the concrete
- Allow the mix on the repair to cure, according to the manufacturer’s instructions. It would normally take at least 24 hours. Some people suggest lightly covering the repair with a tarp after a couple of hours, for extra protection while it cures
If you’re using a tube of concrete crack sealant, it’s even easier. This is one of those incredibly satisfying jobs and you can easily get a good-looking result. Make sure you choose the color of sealant that’s the closest match to the surface you’re working on. Bluestar, for example, offer two shades of gray.
- Prepare the sealant bottle as per manufacturer’s instructions (usually, shake well then snip off the nozzle
- With a steady hand, follow the line of the crack with the nozzle, gently squeezing out the sealant
- Go over the line with a putty knife, smoothing the ribbon of sealant into the surrounding concrete
- Allow to cure, again as directed by the instructions
Is it Normal To Have Hairline Cracks in Concrete? (Why is it Cracking?)
Hairline cracks in concrete are perfectly normal. A hairline crack is typically an eight of an inch wide or less, and is caused by shrinkage during the concrete setting stage.
Crazing cracks are similar. These fine surface cracks resemble shattered glass, and is caused if the concrete loses moisture too quickly.
These cracks are rarely structural, and the main problem is aesthetic. Being so fine, they’re fiddly to fill; however a sealant with a narrow nozzle should help you get the job done.
What Happens if I Don’t Fill The Cracks in My Concrete?
You may choose not to bother filling hairline cracks. That’s fine when the concrete is new and shiny; however, with time, when dirt and dust and goodness knows what else becomes trapped in these cracks, they’ll develop unsightly dark lines that are impossible to keep clean. If they’re in a highly visible area (such as by your front door or on the patio), you may decide that they definitely need filling for cosmetic reasons.
There’s another reason that you may decide to repair narrow cracks: if they’re growing. Most hairline cracks form very early on in the concrete life cycle, caused by the mix and the drying process. So, an “active crack” (one that’s growing) needs repair, and you’d be wise to get it checked out.
The same is true for larger cracks. A static crack is rarely cause for alarm; however if it’s expanding, speak to a professional so you can find out the cause of the crack.
If the crack seems stable, again, repair it for aesthetic reasons. It’ll trap dirt, mud, bits of leaf and grass, water… Wider cracks can also be tripping hazards and can even catch a high heel.
Have you spotted a larger concrete crack that’s wider than a credit card? Step away from the ready-mix patch filler: this is something for a structural engineer to diagnose and treat.
If you’ve got cracks developing in your patio or pathways – or perhaps on your driveway – then you need to deal with them fast or water, dirt and weeds will get in there and quickly make things worse.
Laying concrete is expensive, so the last thing you want is hairline cracks becoming larger cracks, then turning into holes. Next thing you know you’ll have a pile of rubble where the smooth concrete used to be.
That’s why following the simple advice on this page is a good idea if you want to nip this problem in the bud. Filling concrete cracks is not hard and it’s one of those jobs that’s surprisingly satisfying. 🙂
Homeowner and property investor Larry Jones founded Take a Yard in 2020 to bring you the very best outdoor living content, based on his years of experience managing outside spaces. Read more >