What is spalling in concrete and how to fix it

What is spalling in concrete and how to fix it


If you don’t know what is spalling in concrete, the only thing you need to do is take a look at some old concrete buildings. You might see that the surface is crumbling and the rebar might be showing under the reinforced concrete.

It’s not a flattering sight so what causes concrete spalling? There are multiple possibilities from chemical reactions to exposure to fire, but most likely cause is the corrosion of reinforcement in the concrete, the rebar.

Sometimes you might get it fixed if it happens during warranty time. If it happens after that, following will help you to fix it yourself.

Spalling concrete

Spalling concrete causes mostly cosmetic harm at first. The rebar is showing and at first maybe only small concrete pieces are falling off.

After some years, the surface might be attached to the concrete by mostly goodwill and if it’s located high above the ground, some spalling concrete repair should take place. Before the loose concrete falls on someone.

Concrete spalling repair products that I’ve used are most often polymer-modified and there is some fiber-reinforcement in them. The most modern ones act as corrosion protection as well so they can be placed around the cleaned from rust rebar.

Difference between concrete spalling and scaling

Concrete scaling and spalling are quite similar to each other and are most often mixed. Concrete scaling happens on the surface of the concrete, mostly because of freeze-thaw, and it causes the surface to wear or flake off.

Concrete delamination is similar to scaling, but it is not the same. Where scaling can be something like concrete flakes, delamination is bigger concrete pieces, mostly from the concrete surface cream, coming off.

The easy way to spot them is by running a hammer on top of the concrete surface. Healthy concrete gives that nice ringing sound while delamination sounds more like a hollow drum. The same way can be used to spot loose rendering from the concrete surfaces.

So what does it all have to do with spalling? Spalling happens much deeper in the concrete. Normally rebar should be around an inch deep in the concrete surface so it won’t rust so easily.

If that rebar is victim of corrosion, it’s getting moisture somewhere and if it’s that deep, it’s not on the surface level anymore.

how to repair spalling concrete ceiling

How to repair spalling concrete wall

The concrete spalling repair procedure is quite simple, to be honest. You need few tools to be able to do it. Mostly hammer drill with chisel head, an angle grinder with a masonry blade, wire brush for removing the rust from rebar, water and trowel and bucket.

Step 1: To begin with spalling concrete repair, we use the hammer drill (or hammer and chisel if going the hard route) to remove the loose concrete from the top of the rebar and behind it.

You should have 2-3 inches of healthy rebar from the ends of the rebar when you stop removing the loose concrete. Other than that, you should be able to place your finger behind the rebar and on the sides of it.

Why dig it out this way you ask? This way when you place the polymer compound patch, it gets around the rebar and protects it from corrosion. If you leave it to rust there, the patch will come out later after few years. We fix for decades.

Step 2: Now you have rebar you can see here. If it’s near the surface level you might need to cut it with an angle grinder. I mean less than ½ inch from the surface. It’s not doing much there anymore.

If it’s inch deep or can be placed inch deep, leave it there and remove the rust with wire brush.

Step 3: Now you should use water to clean the spalling area free of dust. Garden hose with water will do, pressure wash is the best to get all the dust and lose concrete off. I’ve seen some use watering can even, but it’s not as effective.

Step 4: When the surface of the spalling area is moist, but not dripping water wet, you can mix the polymer patching compound and spread it on the area. Refer to manufacturer label how much water you should use with the product.

You can begin filling the patch edges with a smaller trowel, pressing the patching compound with medium strength to the wall. The cement in the compound will adhere to the concrete surface and because the wall is moist, it won’t suck all the water from the cement so it will adhere well.

Don’t mix the patching compound with too much water as it will make it too weak and it won’t be good for thick patches. Some spalling are so deep that you can’t patch them with one try. Check the manufacturer label to see how thick you can patch.

When you have filled the spalling to surface level, use a finishing trowel to screed the extra off so it will be level with the rest of the surface. You can use sponge float or something else if you want to smooth it out.

If the wall has texture, you will have to imitate it once the patch has cured.

Step 5: Water the patch for 3 days 2 times a day. Check again what the manufacturer recommends. The water will help it to cure strong. Don’t use a pressure washer or garden hose. Just a spray of water is enough so the surface gets a little moist.

To repair crumbling concrete wall we will need to go through every spot like this.

How to repair spalling concrete ceiling

Overhead concrete repair methods are pretty much the same as the wall ones. You need to remove the loose concrete, expose the rebar, remove rust and wash the concrete surface dust-free.

You most probably have a floor you need to protect so spread plastic on it, or cardboard, before you start filling the patch. The process is the same as with the walls, you just can’t fill them so deep because the gravity will make the big patches fall down.

Reinforced concrete repair on the ceiling can be the most enraging experience if you try to be too greedy. Just fill them enough that it will stick and make a comeback the next day.

How to prevent concrete spalling

Spalling concrete foundation is something I see quite often, same goes for most unprotected surfaces. Yes, there is new concrete spalling all over the world.

The best way to prevent concrete from spalling is doing protective layers on top of it. If it’s the floor, maybe coating like epoxy or some sealer. If it’s a wall, there are different protective paints.

If there is water on the wall surface, can it be protected from falling rain most of the time? If the floor has standing water, can it be directed outside the slab?

If concrete ceiling (like balconies) is wet from rein, can a notch be made to it so it will fall off from the edge?

Best way to prevent spalling is to stop the rebar corrosion.


What is spalling in concrete should be pretty clear now and how to fix the situation. At first it’s cosmetic trouble, but if left untreated it can get out of hand.

It’s also big part of curb appeal for me, maybe because I fix these things quite a lot, and I don’t like seeing it on my own property.

I know there are lots of products for fixing concrete spalling. I would always look at what they promise like are they protecting from corrosion, how thick can they patch, how much pull strength it will take to pull them out, etc.

Adhering strength and corrosion protection are the biggest things I look for.