Learn when self-leveling concrete works, why it often fails on old slabs, and alternative options that actually last.
Can you pour self-leveling concrete over existing concrete?
Yes, you can pour self-leveling concrete over existing concrete.
The real question: Should you?
Self-leveling concrete sounds like a quick, simple fix. And in some cases, it works great, but in the wrong spot? You may be looking at cracks, flakes, and failure — fast.
At A-1 Concrete Leveling, we’ve seen it all: the garage floor that peels a month later… the patio slab that flakes by spring. To help you avoid those and similar headaches, we made this guide (and the video above). So you can decide if self-leveling is the right call or if your slab needs something that actually lasts.
TL;DR
Self-leveling concrete can smooth out dips in indoor slabs—but it won’t fix sinking concrete, and it often fails outside. If your slab is cracked, settled, or exposed to the elements, options like leveling, resurfacing, or replacement will last longer and cost less over time.
In This Article
How Self-Leveling Concrete Works
Self-leveling concrete is a thin, pourable, cement-like mix that flows across the surface and settles into a similar-to-concrete-but-different way to create an even surface texture. It doesn't actually lift sunken slabs, it just fill in dips or minor imperfections.
Pro Tip: Self-leveling concrete is not recommended for leveling out parts of slabs that have settled or dropped. More on that below.
Why Self-Leveling Concrete Often Fails
The name "self-leveling" can be misleading because it doesn’t actually "level" concrete that has dropped or settled... it just adds layers on top of it. If the original surface underneath moves, shifts, or wasn’t prepped correctly, the new layer can crack or flake.
- Pouring too thick (over 1/4")
- Using outdoors (freeze-thaw cycles = disaster)
- Applying over dirty, oily, or chipped surfaces
- Expecting it to fix settling or structural issues
When Self-Leveling Concrete Can Work
- Indoors, on smaller areas
- Poured thinly (1/8" to 1/4")
- Applied after proper preparation
- The foundation beneath the concrete is strong, but has dips or uneven trowel marks
When to Avoid Self-Leveling Concrete
- On exterior concrete slabs (garage, patio, driveway)
- When thick layers are needed to cover imperfections
- The concrete is cracked or sinking
- Vertical surfaces (walls, non-horizontal surfaces, etc.)
- You're trying to cover a large surface area
Pro Tip: Each self-leveling compound is different and cures at varying times. Some are ready for use in 12 hours while others require 24-48 hours.
Self-Leveling Prep Steps Most People Skip
Self-leveling concrete is designed to be used over existing concrete to achieve a flat surface, either as a standalone floor or in preparation for flooring to be installed on top.
To ensure a quality application that will last, the existing concrete must be prepared beforehand.
Degrease and clean the concrete completely- Degrease and clean the concrete completely
- Fill holes or gaps to prevent leaks
- Prime the surface with manufacturer-recommended primer
- Ensure no loose chips, paint, or debris remain
Skipping these steps leads to poor bonding—and failure. These imperfections can cause the self-leveling concrete to chip, crack, or deteriorate.
Alternatives for Uneven or Sinking Slabs
If you're dealing with sunken concrete, outdoor slabs, or dips deeper than 1/4", self-leveling compound probably won't last. These methods often provide a more durable, tailored solution:
| Alternative | Best For | Cost Range | Notes |
|
Self-Leveling |
Indoor Surfaces | $ | Sits on surface. Doesn't bond well. |
|
Concrete Leveling |
Most Sunken/Settled Slabs | $$ | Fills void beneath slab. Long-lasting solution. |
|
Resurfacing |
Cosmetic Refresh | $$ | Some overlays can add a layer of protection. |
|
Patching Compounds |
Divots, Chips | $ | Sits on surface. Does not bond well. |
|
Grinding |
Minor Trip Hazards | $ | Quick, cheap. Exposes concrete's pores. |
| Replacement | Concrete Damaged Beyond Repair | $$$ | Should be explored after repair methods |
Concrete Leveling (aka Slabjacking)
Concrete leveling is a repair method used to lift sunken or settled slabs by injecting material underneath to fill voids, eliminate trip hazards, and redirect water flow away from buildings. It does not affect or change the surface texture.
Pros: Long-lasting, addresses root cause
Cons: Despite being filled, drill hole sizes vary
Works on: garage floors, sidewalks, driveways, interior slabs, pool decks, basements, etc.
Resurfacing
Professional resurfacing can be a more permanent fix for uneven surface texture on exterior concrete slabs, but it is a much more expensive and involved process.
Pros: Permanent and durable
Cons: More expensive and labor-intensive
Patching Compounds
Additional concrete and patching compounds are sometimes used as temporary fixes for divots, chipping sections, or trip hazards.
Pros: Good for filling small chips, divots, or minor damage
Cons: Like self-leveling, more of a short-term solution that can also fail with natural concrete movement
Concrete Grinding
Used to eliminate high spots or small trip hazards. Doesn't address dips or voids.
Pros: Quick, cheap, and DIY-friendly (don't forget your PPE!)
Cons: Exposes absorbent pores, making it more susceptible to damage
Concrete Replacement
When slabs are severely cracked, deteriorated, or structurally unsound, replacement is the most reliable option.
Pros: Provides a clean slate
Cons: Most expensive option and may not fix the cause of settled slabs
Best for: Severely damaged outdoor slabs, structural failures, or slabs beyond repair
Top 4 Problems With Using Self-Leveling Concrete
Learn about the common problems you can run into when using self-leveling concrete on uneven slabs.
Can You Use Self-Leveling Concrete Outside?
Again, yes, you can. But due to temperature swings and moisture, outdoor slabs expand and contract over time. As a result, self-leveling compound can crack, crumble, or flake away.
Should You Use It?
If your slab is flat but flawed—and you’re indoors with good prep—go for it. Self-leveling compound can create a smooth finish fast.
But if you're dealing with dips, drop-offs, or outdoor slabs? It may be best to skip it. You'll likely end up with a cracked layer and a bigger headache later.
Instead: get a trusted pro to look at the root of the issue.
A-1 Concrete Leveling offers concrete cleaning, sealing, caulking, and leveling services to restore your surface.
Frequently Asked Questions
Can I pour self-leveling concrete over cracked concrete?
Only if the cracks are filled and stable. Even then, there's risk of failure if the slab is still moving.
Does self-leveling work on garage floors?
Sometimes. Only if it's an interior garage with no major settlement and proper prep is done.
Can I use self-leveling concrete outside?
Not recommended. Temperature swings and moisture make it unreliable outdoors.
How thick can I pour self-leveling concrete?
Most products recommend 1/8" to 1/4". Over 1/2" gets risky.
What if my slab is sinking?
You need concrete leveling—not a surface layer. Otherwise, the problem continues underneath.
Want to learn more? Check out these articles:
Top 4 Problems With Using Self-Leveling Concrete
Discover the options you have when it comes to uneven concrete - indoors and outdoors.
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