Fast setting concrete is super convenient in a lot of situations. Being able to leave a fencepost alone after only an hour or two is really nice when working on a new fence. This means you won’t have to hold it up or find support for it for a long period of time.
Fast-setting concrete is as strong as regular concrete. Concrete gets its strength from a chemical reaction between lime and water, which binds the aggregate to the fill. After it has had time to cure, concrete can reach strengths between 4000 and 5000 PSI.
If Fast-setting concrete is the same strength as ordinary concrete, then what’s the difference between them?
This is the most important distinction between fast-setting and regular concrete. A 50lb bag of fast-drying Quikrete costs an entire dollar more than the equivalent in regular concrete. While for small projects this may be a negligible amount, it can add up very quickly.
Because of this, the economical choice is almost always to use regular concrete rather than Quikrete. Even a few square feet can take more than five bags of concrete to pave. With quick-setting concrete that can add up fast, especially considering the sheer amount of concrete that’s needed to fill even a small space.
Concrete is measured by its volume and its weight. 1 cubic foot of concrete weighs about 150lbs. That means to fill up a space the size of nine subway footlongs arranged into the frame of a cube, you would need 150 lbs of concrete.
And because concrete usually needs to be at least 3 inches deep, it doesn’t take that much space to end up filling a cubic foot. This means that even a project that looks small at the beginning can end up needing hundreds of pounds of concrete, and using fast-setting concrete will cost you an extra dollar for every fifty pounds you need.
The most common use for fast-setting concrete is probably setting fenceposts, but one fencepost will usually need at least 50lbs worth of concrete. This means that to set up just ten fenceposts in fast-setting concrete you’ll be paying ten whole dollars than you usually would.
When To Use Each
Though fast-setting concrete is expensive, it can sometimes be convenient enough to be worth using, especially when you don’t need very much concrete.
I already mentioned fenceposts, but they are a good example. Using fast-setting concrete, fenceposts can be ready to work on in only an hour as opposed to the eight to twelve hours needed for regular concrete.
Small scale projects that need to be used soon after being poured can also make good use of fast-setting concrete, especially if you don’t need more than 200 lbs of the mix.
It can also be nice if you need to pour concrete but you know it will get cold soon, as cold usually interrupts the curing process. With quick-setting concrete, the concrete can be used lightly even if hasn’t had a chance to really cure.
Regular concrete, on the other hand, will be better for mid-sized projects and projects that aren’t time-sensitive. Pouring part of a new sidewalk, for instance, should probably be done with regular concrete to save money.
A patio would also likely be larger than you would want to use fast-setting concrete for as the price will add up quickly.
Regular concrete is also better in hotter weather, where the concrete will set quicker than usual no matter what kind it is. However, if it’s too hot while you’re pouring concrete, it can have adverse effects on the long-term strength of the slab.
It’s generally best to avoid all temperature extremes when it comes to pouring concrete.
Why Is Quikrete So Quick?
When we speak of the hardening process for concrete, we often use the term drying. However, that isn’t entirely accurate. What’s actually happening is a little bit more complex than that.
As I mentioned earlier, concrete gets its strength from a chemical reaction between cement and water. This reaction is known as “curing.” In normal concrete, curing can take weeks or even months.
However, Quikrete is made using a certain amount of extra cement. This speeds up the reaction significantly, making the concrete harden much faster. There are likely other chemical accelerants involved in the process as well, but Quikrete only lists them as “special cements,” so we don’t know what they are specifically.
Sakrete gives about the same amount of information. Whatever they’re using is apparently a secret, but if nothing else at least we know that whatever it is, isn’t making the concrete dry slower.
An interesting side effect of the curing process being so much faster is that fast-setting concrete can get a bit hotter than ordinary concrete.
Curing is what’s known as an exothermic reaction. That means that one of the byproducts of the reaction is heat. This is true for all concrete, which is why it can sometimes randomly get warm the first few weeks after it’s been poured.
However, the speed at which the concrete cures can affect just how hot it gets. If it uses a slow-curing cement, its heat can be limited by quite a bit. If it has faster-curing cement, it will get warmer.
This is usually harmless. Even while concrete is curing, it won’t usually get hot enough to hurt people unless the ambient temperature is very high. Even when it is very hot outside, it’s extremely likeunly to get hot enough to burn anything.
Fast-drying concrete is the same as ordinary concrete in almost every way. Aside from setting speed, if you can think of something about concrete, it probably applies to fast-setting concrete as well. This is because they are essentially the same substance.
Mixing, pouring, and floating fast-setting concrete is not different from doing those things to ordinary concrete in any substantive way, except that they must be done a little bit quicker to accommodate for the faster curing speed.
If you plan on using fast-setting concrete, be ready to get these things done quickly. Aside from that, treat it the same way you’d treat any other concrete pour.