Recently I had my first really bad experience with making a mold for a plug that I built. This was a big disappointment for me. I had spent about eight weeks building a model of a Porsche 917K body in 1/10 scale that I intended to mold then reproduce. My model was built to fit a Tamiya TT-01 R/C car chassis. I had looked for months on the Internet for a 1/10 scale R/C body of this car with no luck so I decided to make my own.
After many weekends and evenings of gluing, shaping, sanding and more sanding I had a nice looking plug of a model that anyone familiar with race cars of the late sixties and early seventies would quickly recognize as a Porsche 917K.
I followed all of the molding procedures that I have had great success with over the years. I mounted the plug to a parting plan, gave it a half dozen coats of mold release wax, applied two coats of PVA and then I went to work.
I attempted to build the mold on a day that was slightly colder than I would have liked (70 degrees – San Diego weather in December) and I was using a brand of tooling gelcoat that I have never used before but I wanted to move this project forward. My hope was to finish this mold and be able to make parts before Christmas.
Since this is a small project, I mixed the tooling gelcoat and applied it with a chip brush. About an hour later I prepared to lay mat and resin on top of the gelcoat and found that it had not begun to tack yet. Uh Oh!
Since the temperature was a little cooler than I had wanted, I assumed that my gelcoat was just setting slowly. In the past, I have laid mat and resin over uncured gelcoat and found that the heat generated by the resin combined with the resin / mat combination depriving the gelcoat of oxygen will speed the curing time of slow-curing gelcoat. Generally, I don’t like to do this but with the days being short and the temperature dropping, I thought it was worth a try.
Well, it didn’t work! 48 hours later I demolded my plug and found a mess of partially cured and completely uncured gelcoat. In addition to having to remove the uncured gelcoat from my plug, the gelcoat also began to attack the paint, leaving blistered ugly patches on the plug.
I am not sure if I have bad gelcoat, or if my hardener to gelcoat mix was off or if I have some other problem. The weather is warm this weekend – I will mix a small amount of gelcoat and see if it cures for me this time. Meanwhile, back to filling, sanding, painting and preparing the plug for the next attempt.
I’ll let you know how this came out in the next post.
Thanks for your readership and good glassing to you,
Steve
