How do I decide which method (pour-on vs. brush-on) is best for my project?

A "Pourable" mold rubber is mixed and poured over your original model.

Consider this method if your model is;

  • Flat, two-dimensional (one-piece block mold, two-piece block mold)
  • Small, three dimensional (one-piece block cut mold)

Advantages/Disadvantages - Pourable molds are easier to make vs. brush-on molds, requiring less labor.  They also take less time to make, meaning you will have a mold you can use same day or early next day; however, you use more material to make a mold so your material cost is higher.

An easy to use pourable mold rubber is our Mold Star® series (https://www.smooth-on.com/product-line/mold-star/), which are easy to use, low viscosity platinum silicones with a convenient mix ratio of 1 part A to 1 part B by volume.


 

A "brush-on" mold rubber is mixed and brushed onto your original model in layers.  After all layers cure (usually overnight), a rigid support shell (also known as a "mother mold") is applied the next day.

Consider this method if your model is:

  • Either two dimensional or three dimensional
  • Small or large
  • Affixed to a vertical surface (like the side of a building) or on a horizontal surface (like a ceiling)

Advantages/Disadantages - Less material, over all, is used to make a brush-on mold so your material cost is less.  However, brush-on molds take more time and effort to make (much more labor vs. a pourable mold). Making a brush-on mold is also more challenging and therefore requires a lot more pre-planning.

A simple to use brushable mold rubber is our Rebound® series (https://www.smooth-on.com/product-line/rebound/), followed by a Plasti-Paste® II (https://www.smooth-on.com/product-line/plasti-paste-series/) for a rigid support shell/mother mold.

Disclaimer
This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.