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Concrete Molds | The Beginners Guide

Concrete Molds | The Beginners Guide

The Beginner's Guide to Casting Molds

So, you want to cast unique concrete or cement-based things without breaking the bank, but not sure where to start? For many, a few YouTube tutorials or DIY forums may be the first step. Instead of searching for opinions, it's better to simply get your hands dirty. Experience is the best and most reliable teacher. Like Walter White, we spent a lot of time in the lab working with the best ingredients to get the perfect mix. Hundreds of casts later, we've secured the mix that's in a bag! Well, a few bags depending on your application.

Concrete versus cement. Is there a difference?

We hear these two words used interchangeably, but not many know that cement is a concrete ingredient. Concrete is a mixture of cement, aggregates and water. The aggregates are sand, gravel, or crushed stone. Through a process called hydration, the cement and water react to harden and bind the aggregates. The hardening process continues for years and, like a bottle of wine, gets stronger with age.

The perfect mix to cast molds

We sat down with our friends over at CTS Cement Manufacturing Corp. and asked them to break it all down for you. From benefits to techniques, we "aggregate" it for you below.

Rapid Set products reviewed:
• Cement All
• Flow Control
• Concrete Mix
• Mortar Mix

If your eyes are set on recreating the Breeze Blocks of Palm Springs and Florida, then Cement All goes well with our molds, like peanut butter and jelly. The Breeze Blocks may not be designed to take on a structural load but they do provide excellent aesthetics and light penetration when inserted into block walls. Cement All can be poured into molds up to 4 inches deep.

Is your mix too thick and you've already added the recommended amount of water? Warning: adding too much water to your mix reduces the strength and increases the likelihood of cracking. Our friends at CTS Cement pointed us to their Flow Control additive in our quest for the right mix consistency. When Flow Control is added, the material flow increases, to help reach all areas of your mold, and is less likely to trap air bubbles.

Set Control, another CTS product, gives you additional working time if early strength is not required. The combined use of Flow Control and Set Control delivers a more fluid, user-friendly mix.

Are you having a hard time mixing concrete?

Well, you're not alone, and it's a common mistake beginners make. We strongly encourage you to read the bag's recommendations before you start. We like to pour a measured amount of water, mix, check the consistency, and add more water until we have an ideal texture. Adding too much water too fast may yield a soup-like result and, worse of all, give you weak concrete that may end up cracking later. You'll know the mix is right when the ingredients are thoroughly wet, the sides stay put, and the surface is slightly shiny when you break it with a hoe.

You can also make your own concrete by mixing straight cement, sand, and stone. It's a bit trickier than buying a bag of pre-packaged concrete or mortar, but it can give you the exact properties you need. You're going to want to follow instructions that came with the cement and be sure to have your aggregates ready and measured.

As a general rule of thumb, you're going to need one-part cement, two parts sand, and four parts stone. Dump your ingredients together in a wheelbarrow and mix in batches to help prevent your cement from drying out. Once you've completed mixing in the aggregates and the mixture is uniform, create a crater in the center, and add a small amount of water. Slowly mix in the water till the consistency begins to look like peanut butter. Too much water will result in soupy, weak cement. If the sides crumble or fall apart, the mix is too dry and will need some water.

Efflorescence, water, and removing concrete from the mold

If you see a white, chalky residue after the concrete cures, this may be efflorescence. This happens when moisture inside the concrete rises to the surface, bringing soluble salts and deposits them on the surface—commonly seen when using cement types with higher porosity.

Is there such a thing as too much water added to a mix? Well, the answer is maybe, but it depends entirely on your desired results. Adding more water than what is recommended will lower the strength and increase the risk of cracking. Be sure to check the suggested ranges for each product to ensure a workable consistency. We found out the hard way.

When is the concrete safe to remove? What is the ideal indicator that it is ready to be removed from the mold? Color and temperature are two key indicators that the bulk of the reaction is complete. As we quickly realized, when the cement and water mix, it generates heat till it reaches its peak. Fast setting products like Cement All generate a lot more heat than slower-setting, portland-cement concrete. If you're using portland cement in your molds, you may not even notice the heat generation. During this time, the color changes, and the concrete is strong enough to remove once the concrete cools down.

Is this the year to finally tackle your outdoor and landscape projects?

Catacomb fire pits, outdoor retaining walls, kitchen backsplash and fireplace mantle installs… Where are you hiding the skulls of your enemies? Well, we can only help recommend an ideal concrete mix. We uh, no longer have any friends in waste management so you're gonna have to dispose of the bodies yourself. Back to business, we recommend using CTS Concrete Mix for these outdoor applications. The Concrete Mix has large aggregate and delivers an ideal mixture for outdoor elements that will be long lasting for years to come.

Our Wall Tiles, Pavers, and Plaques pair well with CTS Cement All. The mix reaches 3,000 PSI one hour after the final set and exceeds 9,000 PSI in 28 days – a lot harder than the six-pack abs on your New Year's Resolution list.

Comments 13

PacMold on

@Linda, thanks for the note. Sometimes we will make a thin slurry mix and place it into the mold before following that up with a heavier mix of material. The slurry can be pushed around the mold to coat the surface of the mold to get a more smooth finish. Give that a shot, thoughts?

Linda on

I have several decorative molds and got them out of the back shelf to make some again after years packed away. I used a sander under the table years ago to vibrate bubbles out, well it didn’t work so well this time, (different sander) what about adding (sanded tile grout)? would that help reduce bubbles??? The old gal needs some help….Thks

PacMold on

We are unable to respond to the blog comments. Technology Sucks! PLEASE email us at info@pacificmolds.com or call us directly at 951.834.3391


I just ordered a few molds. I want to make Halloween decorations for our front yard. Can I use Plaster of Paris in the molds? I’d like to make the molds in the plaster and stick to foam. Thank you in advance.

Sue on

I just saw this and would like to try it,

Evan on

I am very interested in making the fireplace skulls that are used in the fire . i read you can’t use regular cement or concrete you have to use refractory casting cement . or is it a mixture?

Debi on

Hey Peggy, I’ve cast several of the 8" faces and skulls using paper mache. I buy the pure white non-souring kind at a craft store. They can come out of the mold in about 24 – 48 hours depending on how wet you make your mixture, then take about a week to fully cure, but they’re def light enough to hang on a wall. I stick a wire loop for hanging in the back as soon as I press the mache into the mold.

Tony T Alonzo on

i just got my package today, theses molds are freaking COOL!!!. So i want to do mortar mix, do i need to use a release agent for them?

Naomi on

Just ordered skulls and I will be a beginner. Is there something lite I can use to put on walls and then what do you use to anchor/attache to wall? Thank you

Tracy Boudreau on

What is the best way to remove cement from the mold I recently purchased of the medusa molds and my husband started removing her out and actually cracked my mold not the actual piece itself by the mold so now one of my medusa molds are broken.

Jean on

Using your products, how long does it take for the concrete block to set/dry before mold can be removed and used again?

Peggy on

Is there something light weight to use in molds for walls ?I would like to adhere piece to interior wall but fear it would be to heavy . Thanks

Susy on

Just received my first set of skull molds. Should I use a release agent? Would white mortar mix work satisfactorily? I’m hoping to avoid the “cement gray” color.

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