There’s an elephant in the room, and I think it stepped on my concrete floor and cracked it.
Okay, maybe not, but you’ve still found a crack in your concrete floor, what do you do now?
Maybe you’re thinking, is this going to be a problem? And what is causing it? Will it get worse?
This is a rather simple problem, but stressful for some, mostly because it can inspire mixed emotions from fear to anger. So today, Lets dive deep into the issue of cracked slabs. Since we build slab on grade homes, often called patio homes, for most all of our 55+ communities, this is one area that we would like make sure you’re educated on.
The Case of The Cracked Slab
Before we get too far, lets have a refresher course in concrete physics. Don’t worry, we’ll keep this simple.
Concrete utilizes three primary ingredients: 1- water, 2- cement, 3- aggregate (aka rocks).
When mixed in proper proportions, you end up with a mud that will soon hardened into a rock-solid shape. Hopefully, this shape is established before it hardens. This “mud” as it is often termed, utilizes a chemical reaction that form binding structures with all parts involved. This chemical reaction will last for years after you initially place your concrete. That means, your concrete will keep getting harder as long as you have it.
The first seven days are the most critical time for concrete. The majority of the hardness happens at this time, and contrary to some rumors you may have heard, the concrete is not flexible at this stage. This is why you should never drive on new concrete for a minimum of one week.
The rest of the noticeable hardness happens throughout the duration of that month. After that, the changes continue but at diminishing rates.
While the concrete is hardening, it is also drying. There is a difference. Concrete does not get hard because it dries, the chemical reaction is what makes it hard, the drying is from excess moisture draining into the ground or evaporating into the air.
As the concrete dries, even after it seems hard, it acts a little like drying mud, you know the sort, you’ve seen it after a mud causing rainstorm; it’s filled with a maze of cracks. Concrete does the same thing when it dries, it shrinks.
As concrete shrinks, it has only one place to go, and that is towards itself. However, nobody wants or expects concrete to go where-ever it will: You want it to stay as wide as your foundation, and the Earth that it rests upon doesn’t want to give up on the laws of friction.
So while the concrete is struggling to shrink, forces are trying to keep it from moving. Imagine what would happen to a glass bottle if you secured both ends tight, and then it shrank, even just one millimeter. It would not end well.
This is the reason why your sidewalks and driveways have relief joints cut into them. It’s to encourage the cracks to happen there, instead of through the more flat and noticeable areas that will cause you heartburn. Of course, this only works most of the time, but almost every joint you see, will have a crack in it.
You might also notice that inside your house, there aren’t those huge relief joints that you see in sidewalks and driveways. That’s because those large obvious joints aren’t easy to lay tile and carpet on.
As a general rule of thumb, any slab of concrete over nine feet will crack. Sorry for any of you who say that your basement floor never had cracks in it. You probably just didn’t notice them.
Can cracks be stopped?
There are a few ways to stop or limit cracks. One is to place rebar into the concrete. Like most builders, we do this. Granted, it doesn’t prevent all cracks. We place rebar in several strategic locations to keep the concrete from settling and pulling away from places it needs to be. It also helps lend strength to the slab.
Also, concrete poured in the middle of the summer is going to have more cracks than concrete poured when it is colder. Why? Well, lets think about it. What does the hot Sun usually do to water? It evaporates it quickly. So during the Summer, your concrete dries out faster, producing more cracks. So if concrete is poured in the cooler months, assuming its placed on a good base, it will have fewer and smaller cracks.
There are other ways of avoiding cracks or keeping them to a minimum, but they start getting very pricy. The cheapest of these pricy options is to fill the whole slab with steal mesh. This will still allow cracks to occur, because the concrete is shrinking around all this mesh, and the mesh might not be shrinking with it. The idea though, is that the mesh will keep the concrete from settling or from separating too badly. We do not install mesh, because it’s a high cost additive that doesn’t fully stop cracks from occurring. And since we pour your floor on compacted fill, we’re not worried about settling issues.
The next option, is to use a post-tensioned slab system. This will either keep the cracks from happening at all, or keep them so small that you’ll have a hard time seeing them. The only problem, is that your slab has to be twice as thick and cost 20 times what it normally would.
Generally, you only see post-tension slabs on things like tennis courts or large commercial styled projects where any visible crack really is a problem. They accomplish this by running thick steel cables through the concrete, then tightening and securing them to the outside of the concrete. Essentially, what they’re doing, is creating a gigantic spring every couple of feet that crisscross to suck the concrete into itself. This means that as the concrete shrinks, the steel springs help the concrete shrink across the ground it’s sitting on, keeping any cracks from forming, or at the very least, from separating.
Naturally, this is overkill for most homes.
Should I be worried about the cracks in my floor?
Generally, cracks in your floor are nothing to worry yourself over. The only time that you might be concerned is if the cracks start changing vertically, suggesting that there is some settling happening. On our homes, this is pretty rare, but if it does happen, the settling usually all takes place early on and we’re able to grind or fill the differences.
Ceramic or porcelain tile can struggle over cracks too. Since the concrete will always move just a hair from hot to cold seasons, those cracks might cause havoc for tile, causing joints or even the tiles themselves to crack.
Most good tile companies are used to dealing with this issue, and they’ll often bridge the cracks with products meant for such situations.
Caulking cracks in your floor does very little good. People are often worried about water coming up through the cracks, but on a patio home, your floor is well above any underground water. If you had a basement, then that would be different. Water would always be a concern, but even then, the cracks would do little to stop the water from penetrating, because concrete is not waterproof. It is porous, and water will leach through solid concrete and still flood your basement if it is present.
Once your carpeting and hard flooring are in place, you’ll quickly forget all about those cracks. They won’t be felt under your floor, and they won’t be a place for pests to hide.
Concrete cracks can seem scary at first, but they are common on almost every home that has a concrete floor. If anyone ever tells you that your concrete floor should not have any cracks whatsoever, beware, they don’t know what they’re talking about.