Doctor Ben's How-To #4: "Hot Glue Casting" technique booklet (16pgs color & B/W)
Browsing through my old GAZETTES some time ago, I picked up the January/February 1982 issue. In this long-out-of print magazine, I found an article about casting detail parts. In that article Terry Metcalfe described how he cast parts by melting beads of a thermoplastic called "Makit and Bakit" in RTV molds in an ordinary kitchen oven. Unfortunately, this technique didn’t work out so well for me.
Photo at Right: The author’s HO Scale Hookers Point Lighthouse diorama was awarded First Place in On-Line Displays, Most Photogenic, the Badger Award for Weathered Finish, and the Testors Highest Iron Award at the NMRA National Convention in Atlanta, Georgia, in 1995. Many, if not most of the details on this diorama are hot glue castings.
In one of my earlier careers, I was a Mold Maker/Tool & Die Maker. Although I no longer had the machine shop equipment available to me, I wanted to use the skills I had learned to reproduce some of the tiny details that I had created for my contest winning dioramas.
Photo at left: Some Dow-Corning 3110 RTV rubber molds with hot glue detail parts that have been sprayed with primer to make them show up in the photo. Since this article was first published nearly 30 years ago, there have been many additions and improvements in both the molding process and available products for finishing and weathering hot glue castings. Some of these updates are included in the Addendum pages in this booklet.
So I thought I would try this method. I made RTV molds, and spent many hours trying to cram plastic beads into their tiny cavities and melt them down. I had very little success, and decided that this process was not for me.
The idea came to me that I needed to find an inexpensive way to inject some substance into the tiny cavities in my RTV molds. I wanted to devise a process that was easy to do and would use materials and equipment readily available to the average modeler. I knew it had to be relatively inexpensive if model railroaders were going to use it, because they love to use lots of details.
Photo at Left: One of the most challenging hot glue casting efforts was casting the nearly 200 windows for the Ferry-Morse Seed Co. diorama and then painting the individual window mullions for all of the nearly 200 windows. Some windows looked much better than others. One of the really positive things about casting hot glue windows is that the window pane is cast in clear hot glue, and if done successfully, it sort of looks like wavy glass. Another benefit is that when the hot glue gun tip is dragged across the mold to create the glazing, it is possible to remove small pieces (of what would be the glazing) to create the appearance of broken glass.
That is when I thought of hot glue guns. Why not use one to inject hot glue into an RTV mold? The guns melt a silicon wax substance to 300-350 degrees Fahrenheit. RTV rubber is designed to withstand temperatures in excess of 800 degrees. Both substances are silicone based, so they would not stick to each other. Or would they?
Photo at Right: This front view of the Indian River Fruit Co. diorama illustrates more varieties of details that may be cast using a hot glue gun. Two-part molds do not work as well, due to the probably of capturing air bubbles when the two mold halves are pressed together. Also, creating an acceptable casting requires repeated efforts in order to cast a detail that is complete and quasi-flawless. Most everything in the below photo is a hot glue casting save the window frames and the mailbox.
The only way to find out was to try it. Here I describe the process I worked out. The photos included in this technique show the many variations and possible results of using this process.
Photo at Left: The below close-up image of earliest hot glue casting truck cabs and chassis illustrates the less-than-perfect castings; yet with acceptable additions, they make a believable scene
You may never realize how many headaches I have saved you by describing the ins and outs of this very innovative technique. If you have guts enough to try it, I bet you will be surprised by how many different things you can replicate.
The above images and text are short excerpts from this How-To booklet. The information found in this booklet may not aid in curing world hunger, but this booklet may contain just enough ideas and thought to spur your model thought process to consider alternative techniques and ideas.
Should you choose to try this Hot Glue Casting technique, we invite you to share your trials and tribulations; successes and failures with us. Who knows, you may even create a whole new process that has not been discussed in this booklet. We hope so because we are also interested in learning new techniques and it all begins with communication!