How to Eliminate Cracking When Casting Concrete Planters
When pouring and making concrete planters, you may occasionally discover cracks and fissures appearing in your finished piece. Many times these cracks are superficial and will not largely impact the strength and durability of your planters. However, we understand that you want to produce the best products free of imperfections, and thus this article will explain a few common causes of cracking that happen during or after casting, and how to prevent them!
First, let’s identify the two common types of cracking:
Cracking that occurs during or immediately after pouring and curing
Cracking that emerges after several weeks or months
(Our next Blog post will cover situation #2)
Identify which of these two issues you want to address and jump to that section. There are two very different reasons for these types of cracking and they should be addressed separately.
Cracking That Occurs During Or Immediately After Pouring And Curing Your Concrete
This is the most common type of cracking people will experience. Cracking during this stage is more likely to happen on larger and larger shapes. Most of our small shapes under 5” or so will never experience cracking. However any shapes larger than 5” will likely need to be cured properly to avoid cracking. I’ve identified 7 Common causes for cracking during curing:
1. Too much water used in the concrete mix
(Try reducing the water you add next time. Weigh out your mix every time and keep a record of the results. You want the concrete to use as little water as possible while still remaining flowable)
2. Concrete not mixed long enough
(Try working the mix longer before pouring, ensuring that it is homogenous and smooth)
3. Concrete cured too quickly
(Slower curing is less likely to crack. Slow down curing by using a cure-control additive like Rapidset’s “SET CONTROL” and adding a small amount to your wet concrete, then mix, then pour)
4. Water used is too warm
(Use COLD water to further slow the curing process)
5. Ambient temperature is too warm
(Hotter temps will cause the concrete to set more rapidly. Try casting in a cooler environment to minimize cracking. Ideally between 60*F - 77*F)
6. Lack of aggregate in the concrete mix
(Concrete may crack easily if there is not enough sand or rocks in the concrete mix. If your mix is mostly or entirely cement or mortar, try adding sand to the mix in increasing amounts until you get pots that don’t crack)
7. Too much pigment or other additives
(other additives like Flow Control agents, set control, or coloring pigments can all effect the way concrete cures. Any of these additives if used in excess can cause undesirable cracking and other defects.)
Wet-Curing Concrete For Optimal Performance
Wet-cure your concrete pieces to further reduce the chance of cracking. Essentially a wet-cure is where you keep the top surface of concrete wet for at least 1 hour after pouring. This helps add moisture back to the concrete, and further reduces water-loss by evaporation. First, pour your mold as you normally would, and WAIT 5-15 minutes before you spray down the concrete with water. If you apply water immediately, you will slowen the curing process and potentially end up with a poor surface finish. Wait until the top surface loses it’s sheen, as it begins the curing process the top will start to dry out! Once it seems slightly dry, spray it down with water and cover with a water-soaked rag. The opening of the mold should be completely covered. Let the mold sit still for 1 hour minimum (for cement-all… curing times will differ depending on your concrete mix.) and then remove from the mold as normal.
And that’s all! These are a few factors to understand when battling cracking in your planters. I’m confident with the knowledge presented here you can 100% eliminate any cracking or curing issues. If imperfections still persist, please feel free to contact us via email, or reach out to Buddy Rhodes Concrete products for guidance. Our next blog will discuss how to easily prevent cracking over time with the application of a Acrylic Concrete Sealer.