How to make a Silicone Mold and Castings (for advanced modelers)
How To Make A Silicone Mold
Safety and Precautions: Please refer to the Material Sheet which accompanied your shipment. All products should be used with good ventilation. Skin and eye contact, ingestion and breathing of dusts and vapors should be avoided. It is recommended you use gloves, dust masks, and eye protection.
Types of RTV Silicone Molds:
Practice makes perfect! For first time mold makers, we recommend you make a small mold for practice before attempting to mold a valuable piece.
There are four common types of molds (“Silicone Mold Types and How To Make A Silicone Mold”)
- Block mold: one piece with no negative drafts of undercuts. This is probably the easiest mold to produce. The original part should be placed in the box so the silicone is able to flow around it. If the part is simple, it can be placed in a plastic cup, a disposable plastic container or a wooden box (pine wood not recommended). If you choose a wooden box make sure to seal it properly if it appears to be porous.
- Block mold-multiple piece: This can be made exactly like a block mold and simply cut in half once it cures to remove the part. If you prefer not to cut the mold, partially fill the container and allow it to cure. Then apply a thin layer of release agent, and finish pouring the mold. When the second layer is cured, the mold should easily separate.
- Glove mold-brushed onto the pattern: This requires a thixotropic agent which allows the silicone to be brushed on an original piece without running off the surface. The thixotropic agent can be supplied in the catalyst or as a separate additive. This type of silicone is ideal for building restoration. The silicone can be bushed on an original piece of crown molding, allowed to cure and then be removed. The mold can then be taken back to the mold shop where parts can be cast to produce replications of the original molding. This type of molding is also becoming popular to cast rocks or stones to create molds of fake rocks, rock climbing walls, side walks and props for theme parks. Silicone Moldmaking Instructions!
- Cast Glove mold: This is made by creating a void around the original part in a consistent thickness. It is usually done by forming modeling clay around the pattern and then forming a hard shell around the clay. The shell can be made by using fiberglass, urethane or plaster. After the shell has cured, the clay is removed; creating a void which can be filled by silicone.
include gloves, mixing containers, stirring sticks, a gram scale and a mold box.
There are several web sites which can explain how to build an actual mold box. A brief summary of common mold boxes is listed in the section entitled “Types of molds”.
Determine your Chemistry: There are 2 types of moldmaking silicone materials.
Be aware of which system is best suited to your application
|Pot Life & Demold Time||Varies depending on Catalyst
Not heat accelerated
or can be heat
|Risk of Inhibition||Not likely||YES|
|Shrinkage||Less than .03%||Less than .01% / Nil|
|Durometer||7 – 40||30 to 70|
Preparing the Model:
Porous surfaces, such as wood, should be dried and sealed. A clear acrylic spray lacquer is an acceptable sealer. Also applying a release agent, such as petroleum jelly will aid in easy release of a silicone mold. Because silicone can sometimes bond to surfaces which contain silica, such as glass, cements and natural stone; it is recommended to do a spot test for possible adhesion.
Mixing and Curing:
Stirring individual components before use is recommended. Make sure to weigh and measure accurately. Close containers tightly after use. Products should be stored in their original, sealed containers in an environment that does not exceed 90F. Under these conditions, the product will achieve the expected shelf life. Please refer to the individual products technical sheet to determine the products expected shelf life.
The following procedure is an example of a 10:1 mix ratio addition cure product. Please refer to the product’s technical sheet for mix ratio information:
Mix thoroughly by hand or with mixing equipment while minimizing air entrapment until a homogeneous mixture is obtained. This will occur when the material takes on a uniform color with no visible striations. Scrape the sides and bottom of the container thoroughly several times while mixing. Once mixing * is complete it is recommended that the material be de-aired 2-3 times by intermittent evacuation for a few minutes to minimize any imperfections due to bubbles in the cured material. Typically after releasing the vacuum 2-3 times the mass will collapse on itself at which time the vacuum should be left on only 2-4 minutes longer
*Dispensing machine mixed material does not normally need to be de-aired.
Pouring the Mold:
To pour the mold, begin by pouring a stream of silicone into one corner of the mold box. Allow the liquid to push the air out ahead of it to avoid inducing air into the mold. If you have a highly detailed mold, some moldmakers recommend applying mixed silicones directly onto the detailed area and applying low pressure air before pouring the remainder of the mold.
Please refer to the recommend time to demold on the technical sheet for the individual products. Remember to carefully demold at this point, since the mold has not yet achieved a full cure.
Storing the Mold:
It is best for the mold if it can be stored in the original mold box or on a surface that will stress them the least. If left in a distorted shape for extended periods of time, the mold may not be able to return to the original state. Keep of out sunlight and in a cool, dry area if possible
Creating a two part mold – from creating a clay lay up to making both mold sections and a resin casting. It shows how to fix common situations such as silicone bleeding when they occur.
Designed for the beginner, artist Jon Neill shows how to make an open face mold using 2125 silicone with mold master green catalyst. Then how to cast from the mold using MPK70 casting resin. This video showcases the products and materials sold here on our site.
This Video shows Carl Hill Working with MPK-70 POLYURETHANE CASTING RESIN.
I have been doing molding and casting in resin for about six years now, and had to learn the pitfalls of the hobby by myself. Most of the time I lucked out and things worked well. The freedom of being able to cast replacement parts for incomplete toys and casting parts to use in customizing figures was invaluable. Many long hours were spent in a cluttered garage surrounded by plastic measuring cups, mixing sticks and plasticene. The odor was awful, and the product not always as fresh as one would like.
As a writer for Action Figure Times I have been asked about learning to mold and cast items and it’s been difficult to point readers in the right direction. Now, times have changed and I feel I can finally tell my readers about a superior product. Hobby Silicone. com offers one of the best products I’ve ever had the opportunity to sample and review. I met Michael Knott at this year’s Comic Con and saw the sample pieces he brought with him, that and his honest enthusiasm for his product enticed me to sample Hobby Silicone.
The molding silicone came in a one pound container with a screw on top, the top taped to prevent leakage and to preserve freshness of the product. A simple 10 parts silicone to 1 part hardener mixture was all it took. After mixing I poured it into mold and tapped the mold several times to bring any bubbles to the surface and then I just let it sit overnight to cure. After making both sides of the mold I ended up with a very durable mold that looks like it will last for years of castings! I was using the firm silicone and I just loved it. Sharp details, easy to use and a durable molds are what it’s all about!
I have sampled several sources for polyurethane resin here in California, and have had decent results, but I have always hated the smelly resin and having to step out of my workshop after casting a project . Hobby Silicone resin has nearly no odor, and the casting ends up with a nearly white coloring (not the yellowish finished product in polyurethane) and is very durable, unlike the brittle results I got with polyurethane. My test cast was very easy to do and the resin performed better than I could have hoped for. The parts came out cleanly and quickly. I have no fear of dropping them or handling the piece after it cured, which is also a difference with other resins.
HobbySilicone.com is a user friendly site, with tons of instructional materials to give professional results to even a rank amateur. I highly recommend these instructions if you are just starting out molding and casting. There are illustrations and detailed instructions on how to make molds, and how to cast with silicone.
Another important point to make is that this material, while far and away a superior product than polyurethane is nearly HALF the price. This is a boon to the hobbyist where cost is always a consideration,
I urge anyone who has ever wanted to mold their own project, maybe even copy a sculpt that you are proud of to give Hobby Silicone a try.
Owner, Wheaty Wheat Prototyping Studios
I’ve used a lot of silicones and resins in my career. One of the best suppliers for silicone and resins is MPK Enterprises.
I’ve worked with a few of their silicone products 2125 Blue and green, Brushable silicones, and the 107 soft silicone. All of them performed outstanding, but my favorite is the 2125 Blue. The molds last without tearing, I have molds 3yrs old that are still solid to cast pieces from.
My all time favorite product is MPK 70 urethane resin. I use both the 180 sec and the 10 min. This is one of the best resins I have found it has no odor, sands very easy and has few to no bubbles that gather to details.
The MPK 70 – 10 minute, makes a great product even better. It allows you time to pour big molds with out making you rush, pour molds with heavy details or small parts giving enough time for air bubbles to find there way through tight areas in the mold and lastly it helps when the weather is hot, where 180 sec resin become 2 sec resin, again giving you time to pour and not feel rushed.
As a professional I have been very satisfied with MPK products and services since 2005. I recommend MPK products to all hobbyists and professionals who are looking for a reliable product backed by a reliable company.