Does plastic stick to concrete mold?

The best material for a concrete mold is going to be something that concrete won't stick to. Concrete won't stick to silicone, rubber, or plastic.

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What can you use for concrete molds for crafts? Learn the benefits of using different mold types to help you choose the best one for your project. How to choose the right mold types for concrete craft and what the options are. The world of concrete crafts-making can be complicated, so it’s important to understand which projects require certain concrete mold materials. You see, there are tons of different items you can use as molds for concrete crafts. However, choosing the right material for your mold is going to make all the difference in whether or not your cement craft project is successful. I’m going to explain what the different material options are and for which projects they are best suited, as well as some of the techniques for creating your own concrete molds. -By the way, if you are just getting started then I recommend taking a look at my article on the Concrete and Cement Mixes Tests where I compare six different types of concrete mixes, as well as my experiments with sealers, effects of vibrating, etc. For advanced learning about concrete mix strengths (like why mixes with large aggregate make some things stronger and others weaker) and how to know exactly which concrete mix is best for your project, then take a look at The Best Mix For Your Concrete Project.

What Are Good Mold Types to Choose for Working with Concrete?

There are several considerations when choosing a concrete mold for crafts.

The best material for a concrete mold is going to be something that concrete won’t stick to. Concrete won’t stick to silicone, rubber, or plastic. There really isn’t an ideal material for choosing a mold for concrete crafts, because aside from size shape, there will be a few other factors to look at. Pocket Guide to Concrete & Cement Mixes For Crafts Grab the free pocket guide. It has a handy chart for choosing the right mix for your project. Grab The Guide!

Texture of a Mold

Texture isn’t going to affect whether or not your project is successful from a functional standpoint, but it does affect the aesthetics. If you want a smooth look, then you will need a smooth mold. Smoothness can also equate to shininess. The more glass-like the mold is, the shinier your cement craft will be. Even though silicone is super smooth, it doesn’t have a glass-like feel, nor any sheen of its own. Silicone won’t produce a very shiny piece of cement, but it will be super smooth. Anything that has even the slightest bit of a matte feel or look, will give you a matte result with your concrete/cement. If you’d like more detailed information, I’ve written a post about how to make concrete shin.

Mold Rigidity

*The more flexible the plastic is, the easier it will be to demold, so watch out for plastic containers that are rigid. I have these plastic half-sphere molds that are made to be for bath bomb soaps. Demolding isn’t much of a problem because of the shape. The tapering of the sphere allows it to come out easily from the plastic. Something with straight sides and something deeper will become increasingly more difficult to demold.

Shape of a Mold

Tapered molds are good and will help with releasing concrete. The complexity of a shape will matter as well. Complex shapes tend to have bevels that go in a direction that will cause an undercut. If the concrete can’t slide out easily because of a pocket within the mold, then you may have an issue. The photo above is an extreme example. If you were to try to demold this by turning it upside down, it wouldn’t come out. The only way to get concrete out of this would be to cut it. Often concrete crafts can still be removed from a mold with an undercut, but you probably will have to cut or break the mold to remove your piece.

This also puts your cement crafts piece at risk of getting broken.

Mold Size

The material to use for the mold will depend on size and in each section I discuss which materials are good for certain sizes. In addition, another important consideration is finding the proper size inner mold to fit proportionately to the outer mold. If you are casting planters or dishes, you will need to find two molds that will be sized properly and fit inside of each other.

The thickness of the walls has to be considered.

The two containers should fit together allowing for spacing that is neither too narrow (causing cracking) or too thick (taking up too much space).

These concrete mold containers are not sized appropriately to fit.

The walls will be too thin, so either the sour cream container needs to be wider or the Nilla wafers container needs to be narrower.

These containers provide a better fit.

They will provide ample thickness for the concrete planter walls.

SCALE AND PROPORTION

This is a big one.

You can have a nice smooth plastic mold container that has a slight taper to it, and have another nice smooth container as the inner mold -and still, the inside mold will get stuck. This is likely because of the proportion of the mold to the concrete. When you cast something tall and narrow, you are essentially putting more pressure on that inner mold. If your mold is wide and shallow, there isn’t much weight from the concrete placing pressure on the inner mold piece and so it releases easily.

Pre-Made Concrete Crafts Molds

You can purchase a pre-made mold that is specifically made for concrete/cement crafts.

These are typically a silicone material and sometimes plastic.

Often, the silicone concrete molds are listed as resin molds, so if you are doing a Google or Amazon search to find one, you may get more results by searching for “resin” molds. If you are interested in purchasing a mold, check out my article on 31 of the best and most unique concrete silicone molds you can buy.

Benefits Of Pre-Made Concrete Molds

Rubber and silicone will easily release concrete

Smooth surface (not usually shiny- more matte)

Time saving since you don’t have to make anything or set anything up

Drawbacks

Not easy to modify

Usually cost more than making your own mold or repurposing existing items

Best Uses For Pre-Made Molds

For relying on the mold to produce the exact shape you see

There are no surprises

Here’s an article explaining what’s important to know when looking to buy a pre-made silicone mold that’s made specifically for concrete planters and other crafts. It also has recommendations on where to purchase a concrete silicone mold from.

Pre-made Molds Intended for Other Purposes

There are several types of pre-made molds that work perfectly as forms for concrete crafts.

Baking Molds

This mold was used for a ring-shaped cement candleholder that I made for the Ugly Duckling House. The molds that are made from silicone will function just like a silicone mold made for resin and concrete. You should be able to count on it being just as good as one specifically made for concrete.

Candy-Making Molds

These are also the same as baking molds. If it’s silicone and it’s labeled for candy or chocolates, but it works for your project- then go for it. I used these for the Cement Plant Label Stakes.

Molds for Candle and Soap-Making

Sometimes these candle and soap molds will be silicone, but more often, I have found them to be plastic. If you find a candle/soap mold that is the shape you want, take note of whether that plastic is rigid or not. As discussed above, rigid plastic will be more difficult to demold, but the shape of the mold will either help or hinder the ease of release.

I used bath bomb molds to make these DIY Mini Concrete Bowls.

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Benefits Of Pre-Made Molds Not Intended For Concrete

Release easily

Smooth surface (not usually shiny- more matte)

Time saving since you don’t have to make anything or set anything up

Drawbacks

Not easy to modify

Usually cost more than making your own mold or repurposing existing items

You may run into some demolding issues with a rigid plastic

Best Uses For Molds Not Intended For Concrete

What you see is what you’ll get, so any cement craft you need to make quickly or one that doesn’t lend itself to being made easily using a different method.

Utilizing Existing Items- Repurposing For Concrete Forms

Disposable Items

Plastic Containers as Molds for Cement

Any leftover container from food or beverages. Bowls, cups, Tupperware, sour cream, yogurt, leftover takeout containers from restaurants. I used these types of containers for a marbled concrete planter and modern concrete planter.

Benefits Of Disposable Containers For Concrete Molds

Extremely budget friendly, come in multitudes of shapes and sizes

It’s easy to find containers that aren’t too rigid, and provide the flexibility needed to allow for easy demolding

Drawbacks

Finding the proper size inner mold to fit proportionately to the outer mold

Watch out for containers that have bevels that will cause undercuts

Best Uses

Any small cement craft project. These containers are ideal molds for planters, clocks, dishes, etc.

Unusual Items

Balloons as Molds

Balloons are an incredible tool to use as a cement mold.

You can use it to sculpt with, like you see here in the cement balloon planter or you can use it as mold by casting cement inside the way you see here.

Plastic Balls as Molds

You can cut open just about any type of plastic ball and use it as mold as I did with this Round Cement Christmas Candle and these cute little DIY Magnetic Cement Planters.

Stockings Used for Molds

Nylon stockings work well as mold because they will help hold the shape of your concrete piece and give you lots of flexibility in the shapes you make. And to demold, all you do is pull the panty hose off. Here’s how I utilized pantyhose for the concrete mold with this Concrete Garden Owl Statue .

Hats as Molds

Though I haven’t tried this one yet, you can use things like knit hats as molds. These work similarly to the way stockings do. You can see some neat concrete planters being made using a hat on YouTube.

Concrete Sand Molds

It’s true, you can use sand as mold to cast concrete in.

There’s plenty of youTube videos out there showing this, but no matter how many times I watch them, I can’t seem to get the same results as the people in the videos. Here was my initial attempt at casting a cement planter in the sand- don’t laugh! And my second attempt at casting a concrete planter in a sand mold.

This was a concrete bowl molded over a mound of sand.

Benefits Of Using Unusual Item As A Mold for conCrete

Interesting options and flexibility- can be super creative with your ideas

Low cost

Drawbacks

May require a little bit of skill and patience

Best Uses For Unusual Items As Cement Crafts Molds

Planters and rounded statues

Make Your Own Cement Crafts Molds

When you make your own cement and concrete mold, the sky’s the limit, you just need to use the proper material for your design.

Materials For Building A Concrete Mold

Melamine Boards as Molds Forms

A melamine board is a composite wood coated with a type of plastic resin. The resin is helpful because concrete won’t stick to it. When using melamine as your concrete mold, you will want to use silicone caulk to seal the inside edges.

Assembly

For large forms, you will want to use screws, along with silicone caulk at the seams. To demold, you will just simply unscrew the sides and the concrete should lift out. For smaller forms, I have gotten away with using only caulk. A medium form you can use brad nails and caulk, which will be quicker than screws. You can see how I assembled these two projects. I used screws for the forms for the tiles in the 3D cement tile planter box and just a few nails for the outdoor concrete wall tile.

Benefits Of Melamine For Molds

Relatively inexpensive

Great strength

You won’t have to fight with anything to demold it because it will be easily removable, as you will just disassemble the boards

Drawbacks

May require tools for assembly

Edges need to be caulked

Best Uses For Melamine Forms For Concrete MOldS

Excellent for large concrete molds like large planter boxes

A project needing clean, square or slightly rounded edges

Tiles

Countertops

Tabletops (side tables, coffee tables)

Sinks

Whiteboard

Whiteboard -aka- marker board is a composite board that can come in a thickness of under ¼”. It is the same basic material as a clipboard but has a super glossy finish that people use as writable marker boards.

Assembly

Can be secured with hot glue, tape or caulk

Reusable as long as the marker board coating doesn’t tear

Benefits Of Using Whiteboard as a concrete mold

Easy to cut without using power tools

Inexpensive

Easy disassembly with a utility knife

Drawbacks

May not be rigid enough for larger projects without reinforcement

Edges should be caulked

Best Uses

Medium sized or small molds

Acetate Sheets to Line Molds

Acetate sheets are a plastic film and can come glossy or matte.

They aren’t rigid enough to be used on their own for concrete molds, but are perfect for coating mold materials like aluminum flashing, cardboard and corrugated plastic.

Assembly

Spray adhesive, tape

Benefits

Extremely smooth, glossy sheets will result in a shiny surface

Inexpensive

Drawbacks

An extra step in the making process

Best Uses For Acetate Sheets

Coating any surface that has a texture

Coating surfaces that would otherwise stick to the concrete

Corrugated Plastic Sheets as Pieces for Molds

These are a plastic version of corrugated cardboard. They are easily found at Home Depot and Art/Craft stores like Michaels.

Assembly

Holds together well with tape and/or hot glue

Benefits Of Corrugated Plastic For Concrete Molds

Easy to work with

Inexpensive

Easy to demold

Drawbacks

Corrugated grooves do show up on finished product- acetate sheets recommended to combat this

Best Uses For Corrugated Plastic Concrete Molds

Any small cement craft project

A cavity for a silicone mold to be poured into

This is a project where I used corrugated plastic- Make A Triangle Concrete Planter Mold.

Cardboard for Mold Pieces

This comes as either raw cardboard or can have a waxed coating.

For my twig lights with a floating concrete base, the form tube I used was pre-waxed but I still needed to use an acetate sheet to coat the inside. This is because the lines from the wrapped layers of the cardboard would have transferred onto the concrete. More importantly, the size of it was so large that the amount of water in the mix would have either caused the tube to warp or collapse.

I did the same thing for the concrete side table.

Assembly

Tape or hot glue

Benefits

Inexpensive

Demolds easily if the cardboard is pre-waxed or a waxy lubricant is added to un-waxed cardboard

Drawbacks

Needs to be coated with wax to not stick to the concrete

Unwaxed cardboard will absorb water from the concrete and larger projects will require additional help with an acetate sheet layer added

Best Uses

Excellent as molds for making round cement crafts like these concrete coasters (lubricated with wax)

Aluminum Flashing as a Concrete Mold Material

Aluminum flashing is a fantastic material because it’s bendable.

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You will want to coat it with another material to use for molds because aluminum chemically reacts with cement and concrete mixes and causes an unappealing appearance.

Holy pinholes Batman! Doesn’t it remind you of a loofah sponge?

When I first attempted my triangle Planter using aluminum as the mold, this was the result. It looks like a loofah stone. This can actually be a cool look, depending on your project, but just be aware that by not coating it, you will have this effect. What’s the best way to coat the aluminum? I like coating it with acetate sheets. The sheets are thick enough to eliminate the sponging effect. I have also tried with contact paper, but it’s not quite thick enough. I used the flashing for the molds in these DIY Wine Bottle Lights.

Assembly

Tape or staples

Benefits

Smooth

Flexible -can create any shape, especially helpful for curved shapes

Drawbacks

Chemical reaction causes spongy look

Coating the aluminum is an extra step

May require additional support

Best Uses

Concrete crafts that you want to be round or have curves

Glass

Don’t use glass as a concrete form. It doesn’t allow the concrete to release. The only way to release it is to break the glass, but breaking it without cracking the cement is tough to do.

Best Uses

None

Making Your Own Concrete Molds

Making A Silicone Mold For Concrete Crafts

A handmade silicone mold is about as good of a concrete crafts mold as you can get. Requires mixing 2 parts at a 1:1 ratio.

Benefits Of Using Handmade Silicone Molds

Reusable allowing for many multiples of copies

Provide a consistent and even surface

Many pieces may not require any sanding.

Typically easy to demold

Drawbacks

Silicone is not very budget friendly

Best Uses

Making exact replicas of an object

Making multiple copies of a cement craft

Planters, dishes, bowls

Here are some tutorials where I made silicone molds for planters:

Making A Brush-On Rubber Latex Mold

A latex rubber mold material that is applied by brushing it on in many layers.

Benefits Of Using Rubber Latex Brush-On Molds

Reusable allowing for a fair amount of copies

Provide a consistent and even surface

Pieces may not require very much sanding

Flexible and allows pretty much any object to be easily demolded

Drawbacks

Latex rubber is not very budget friendly, but it is less expensive than silicone

Best Uses

Making exact replicas of an object

Making objects with intricate shapes or undercuts

Replicating objects that have very fine, intricate details

I used a latex rubber mold to make this Concrete Cowboy Boot Planter.

What’s The Best Concrete Mix For Molds?

I knew you were going to ask me that. And guess what?

The good news is that the type of mold material you use isn’t really much of a factor in choosing a cement mix. The bad news is that the determining factors will be the size, shape and texture you intend on having for your concrete piece. I go into a great deal of detail for six different concrete craft mixes in this article, but I can tell you that the smaller the space you are casting concrete into, the easier it will be if you choose a smooth concrete/cement mix. Using a mix like Cement All, Quick Setting Cement or Portland cement at a 3:1 or 2:1 ratio with sand is going to be your best bet. Chances are if you are building a large form, and using melamine, then you can use a low aggregate mix or a higher aggregate mix. You will need to base this decision on the size of the form. The long and short is that the material type really isn’t going to come into play, so let’s celebrate the fact that you can cross that off your worries list.

Release Agents For Cement Crafts Molds

You can use just about any kind of oil for helping cement release from a mold. Many times, my decision on what to use is based on what I have on hand. Your mold may not require a lubricant, and you may want to refrain from using one. Lubricants can cause discoloration of concrete and an increased potential for pin holes. If you need to use a concrete lubricant, then a clear oil shouldn’t discolor the concrete, but an oil with a tint to it like vegetable oil/spray or motor oil, can change the color. For details, please see my Cement Tests where I did experiments on both discoloration and texture effects from using lubricants.

Vaseline

Vegetable or other oil spray

Johnson’s paste wax

Baby oil

Mineral oil

Motor oil

I rarely use a release agent for my cement crafts molds, but sometimes it is necessary. If the material you are using as mold is porous, then it is recommended to use a lubricant. Wood is an example of a porous material that may require a release agent. When I made the tile for my outdoor wall decor flower tile, I used paste wax on the wood that I used to create the frame of the mold.

Methods for Removing Concrete From Plastic Molds

Hot Water

I have had some success with releasing molds from plastic by heating the inside with very hot water. To do this, put a pot of water and the stove and get it hot- not boiling, but a bit before it boils. Then carefully pour it into the inner mold. Wait a few seconds, and take care to not burn yourself, then pour it out. Use pliers to pull it out. You can also do this with an outer mold by placing it in a larger bowl of the hot water for a few seconds. The water will soften the plastic, enabling it to let go of its hold. It also may contract when it cools, which will also allow it to be removed.

This doesn’t always work but it is worth a try.

Heat Gun

A heat gun works for many plastic molds much in the same way the hot water method does, but it is more convenient, safer and less messy. Just wave the heat gun back and forth over and around the plastic. Sometimes the cement crafts piece will even drop right out.

Craft Knife or Utility Knife

Most plastic molds will come out just by simply cutting the plastic off. Between the heat gun and utility knife, I can always get concrete out of a plastic mold.

Heat Tool

This is one of the first methods I tried for removing a plastic mold from concrete. A heat tool takes a little bit of patience and the smell of burnt plastic isn’t pleasant, but this will work. Take care not to burn yourself,and don’t hold it in one spot for too long or you risk charring the concrete.

Needle-Nose Pliers

Needle-nose pliers are definitely necessary for many molds because they can grip surfaces that are too small for your fingers to grip, and they aren’t likely to slip. Sometimes I can remove a mold with these alone, but usually these are used in conjunction with a utility knife or heat gun. As you can see the options really are practically limitless for what you can use as a concrete crafts mold. Hopefully now you’ve got solutions for all those cement projects you’ve been brainstorming. Here’s the full list of supplies you’ll need for concrete crafts and why you’ll need them.