What’s in your mold release?

March 15, 2021

We sell a fair number of products related to mold making, but the one that we get the most questions about are mold releases.  Some folks don’t know why they need them, or they don’t know what the difference is between the different kinds of mold releases and when to use the different mold releases.  While I have no doubt that we’ll continue to get these questions in the future, I hope to start to address some of them here.

Why use mold release?

Mold release products are special materials that create an interface between the mold and the part being cast from the mold.  These are often available as liquids, pastes, or aerosol sprays, but regardless of the delivery method they all are designed to help maintain and extend the functional lifespan of your mold by making it easier to remove the finished piece from it.

Old mold still going strong!

Applying some Petrolease aerosol spray to an old mold to help keep it going.

Every time you cast a piece in a mold, friction and stress are created when the piece is removed.  This friction and stress will eventually cause pieces of the mold to tear off and break down, leaving you with an imperfect cast.  In some cases, inspection of the cast piece after you remove it from the mold will even reveal chunks of the mold lodged in the piece that have to be removed.  This is normal behavior for molds, flexible and rigid alike!  Molds will break down over time and have to be remade to maintain the accuracy of the pieces that they produce.

This where mold release products play their part: by lubricating the mold and reducing friction and other stresses in the mold itself, the mold will stay undamaged for longer times, allowing you to get more use out of it before you have to create a new mold. 


What to use and when

Once you’ve made the decision to use a mold release product with your molds, the next question is what to use and how. Though the function of mold release may be universal, the specific compounds in use are not.  For example, if you are using a silicone mold, a silicone-based mold release (sometimes sold as a “universal” mold release) is not going to provide as much lubrication and can sometimes cause parts to adhere to the mold.. 

Using paintbrush to touch up some sprayed Petrolease

Using paintbrush to touch up some sprayed Petrolease

Working with silicone molds, your best bet is to use a petroleum jelly based mold release, like Price-Driscoll’s Petrolease spray.  While you can macgyver your own mold release with petroleum jelly and denatured alcohol, we find that Petrolease is a very convenient and user-friendly mold release for use with silicone molds.  Applied as an aerosol spray, you can touch it up with a paintbrush after the propellant has evaporated to get any spots you might have missed, and then pour in your casting material and go.  This is a very easy to use and reliable mold release for use with silicone molds and one that we can whole-heartedly recommend for a wide range of silicone projects.

Parfilm mold releases are an interesting group of mold release products with more specialized applications.  We currently carry Ultra 4 Urethane Parfilm and Ultra 4 Epoxy Parfilm aerosol mold release by Price-Driscoll for users who have need for these specialized products. 

When you are casting small amounts of epoxy resin (such as our 300/21 Epoxy Resin system) into a silicone mold, epoxy parfilm helps to ensure you have a detailed cast with a smooth removal without any interactions that petroleum jelly can cause.  Simply apply the spray, touch up with a paintbrush and then wait for it to dry.  Once it has dried after 20-30 minutes, you can pour in your epoxy and allow it to cure.  It’s that easy!

When using urethane in silicone molds, such as our AeroMarine Products Casting Resin and AeroMarine Products Black Casting Resin, a urethane parfilm can be used for mold release.  We carry Ultra 4 Urethane Parfilm for this purpose which is an aerosol spray like the Epoxy Parfilm but is specifically formulated for use with urethane products in silicone molds.  Once applied via aerosol, the liquid film can be touched up with a paintbrush to ensure full coverage of the mold, and then once it has dried after 20-30 minutes you can apply your urethane resin and finish the casting.  There are a number mold release solutions available for urethane resins, but we feel the combination of convenience and reliability of the Ultra 4 Urethane Parfilm makes it a clear winner and well worth it.

While mold release isn’t always necessary for use with silicone molds, if you have a project that calls for many parts cast from the same mold it can be an invaluable asset for preserving and extending the life of your mold.  Choosing the right mold release can ensure that your project will not get tripped up by premature breakdown of your molds.  As always, if you have any other questions or comments please give us a call at 1-877-349-8860, or send us an email at info@aeromarineproducts.com.

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