One of my things is restoring older Rivarossi articulateds. Because parts are almost impossible to find I decided to make my own parts. I bought a casting kit from Micro-Mark (Complete Resin Casting Starter Set) and proceeded to make molds. That was about 6 or 7 years ago, I made over 40 RTV silicon molds for my locomotive parts and miscellaneous general parts.
This evening I was going to cast more parts as my supply had depleted. To my surprise almost half of the molds are no good, they have cracked and generally fallen apart.
I was wondering what I did wrong; they were stored in a closet off my hobby room so it wasn’t a temperature related problem.
I lucked out in that the mold I needed the most is OK and I can make the air horns I need for my E7As.
I do a lot of molding and casting. I’ve used Dow Corning RTV Type HSIII. I’ve got some molds that are approaching the 10 year mark and still are in excellent condition. They have no tears or loss of detail and are still flexible. They are stored in my basement so they get no special treatment. Alumilite currently is selling their own brand of the HSIII and I have had great results with it also, just as not as long of history. Alumilite has several RTV’s so try to get the kit that is of that type. Perhaps call Alumilite and order direct from them or order off their website. No affiliation with them- just a satisfied customer.
Mark B.
ps- Sometimes the resin that is used can accelerate the degradation of a mold.
I’m using Smooth Cast 300 for some detail pieces and it doesn’t seem to have degraded the molds at all.
I have been using the Micromart silicone for about 15 years. I have had some molds disintegrate after about 5-10 years, most however have held up. I don’t know why some do disintegrate but they do. Maybe you should change brands.
If you want to repair some of the molds enough so you can get one more casting out of them to make a new master, you can use the RTV as a “glue”.
I recently tried (successfully) my hand at casting some RPO windows for a kitbash project; before I started I read a lot of articles and one suggested to store molds with a casting in them so the mold won’t warp or shrink over time. Another benefit of doing this is if the mold does get damaged, you have a good master to remake another mold.
I just used the Easy Mold Silicone Putty and the Amazing Casting Resin from Michael’s craft store…it worked quite well and I’m looking forward to casting more stuff.
This issue has really stirred my pot, it has put me in a research mode for the last two days. Come to find out the instructions that came in the Micro-Mark Casting Kit leave a lot to be desired.
I went to several manufacturer sites and all have very good videos showing the proper way to use their material. I did much better doing a RTV mold casting search on YouTube. I found out I was doing it wrong, I would recommend that any newbie to casting checkout the many How To Videos on YouTube.
I haven’t found out any information on why my 6 or 7 year old molds fell apart. Doing a little thinking about my progression in making the molds it might have been just a bad or a too old in stock kit from Micro-Mark, both RTV and resin